CELGENE CORP /DE/
S-4, 2000-07-26
COMMERCIAL PHYSICAL & BIOLOGICAL RESEARCH
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     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JULY 26, 2000
                                                     REGISTRATION NO. 333-
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                              ------------------
                                    FORM S-4
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                              ------------------
                              CELGENE CORPORATION
            (Exact names of registrant as specified in its charter)
<TABLE>
     <S>                                <C>                            <C>
               DELAWARE                           2834                    22-2711928
    (State or other jurisdiction of   (Primary Standard Industrial     (I.R.S. Employer
     incorporation or organization)    Classification Code Number)   Identification No.)
</TABLE>
                              ------------------
                               7 POWDER HORN DRIVE
                            WARREN, NEW JERSEY 07059
                                 (732) 271-1001
              (Address, including zip code, and telephone number,
       including area code, of registrant's principal executive offices)
                              ------------------
                                JOHN W. JACKSON
               CHAIRMAN OF THE BOARD AND CHIEF EXECUTIVE OFFICER
                               CELGENE CORPORATION
                               7 POWDER HORN DRIVE
                           WARREN, NEW JERSEY 07059
                                 (732) 271-1001
                    (Name, address, including zip code, and
         telephone number, including area code, of agent for service)
                              ------------------
                         COPIES OF COMMUNICATIONS TO:
                            ROBERT A. CANTONE, ESQ.
                               PROSKAUER ROSE LLP
                                  1585 BROADWAY
                         NEW YORK, NEW YORK 10036-8299
                                 (212) 969-3000

APPROXIMATE  DATE OF  COMMENCEMENT  OF PROPOSED  SALE TO THE PUBLIC:  As soon as
practical after the registration  statement  becomes effective and the effective
time of the proposed  merger of Celgene  Acquisition  Corp. with and into Signal
Pharmaceuticals, Inc., as described in the Agreement and Plan of Merger dated as
of June 29,  2000,  attached  as  Appendix  A to the proxy  statement/prospectus
forming a part of this registration statement.
If the securities  being registered on this form are being offered in connection
with the  formation of a holding  company and there is  compliance  with General
Instruction G, check the following box. [ ]
If this form is filed to register additional securities for an offering pursuant
to Rule 462(b) under the  Securities  Act,  check the following box and list the
Securities  Act  registration  statement  number  of  the  earlier  registration
statement for the same offering. [ ]
If this form is a  post-effective  amendment filed pursuant to Rule 462(d) under
the  Securities  Act,  check  the  following  box and  list the  Securities  Act
registration  statement number of the earlier effective  registration  statement
for the same offering. [ ]
                              ------------------
                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
==============================================================================================================================
                                                                 PROPOSED MAXIMUM       PROPOSED MAXIMUM
 TITLE OF EACH CLASS OF SECURITIES TO BE      AMOUNT TO BE      OFFERING PRICE PER          AGGREGATE            AMOUNT OF
                REGISTERED                   REGISTERED (1)          UNIT (2)          OFFERING PRICE (2)     REGISTRATION FEE
-----------------------------------------   ----------------   --------------------   --------------------   -----------------
<S>                                         <C>                <C>                    <C>                    <C>
Common Stock, par value $.01 per share.        4,144,255             $ 44.25            $ 183,383,283.75        $ 48,413.19
==============================================================================================================================
</TABLE>
1. This  Registration  Statement  relates  to common  stock,  par value $.01 per
   share,  of the  Registrant  issuable  to  holders  of common  stock of Signal
   Pharmaceuticals,  Inc.  ("Signal")  in the  proposed  merger.  The  amount of
   Registrant's  common stock to be registered  represents the maximum number of
   shares that may be issued to former holders of securities of Signal  pursuant
   to the merger.
2. Based on the average  high and low trading  price of the common  stock on the
   Nasdaq National Market on July 25, 2000. Estimated pursuant to Rule 457 under
   the  Securities  Act of 1933,  solely  for the  purpose  of  calculating  the
   registration fee.

THE REGISTRANT WILL AMEND THIS  REGISTRATION  STATEMENT ON SUCH DATE OR DATES AS
MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE  REGISTRANT  SHALL FILE A
FURTHER AMENDMENT WHICH  SPECIFICALLY  STATES THAT THIS  REGISTRATION  STATEMENT
SHALL  THEREAFTER  BECOME  EFFECTIVE  IN  ACCORDANCE  WITH  SECTION  8(A) OF THE
SECURITIES ACT OF 1933 OR UNTIL THIS  REGISTRATION  STATEMENT  SHALL  THEREAFTER
BECOME EFFECTIVE ON SUCH DATE AS THE SECURITIES AND EXCHANGE COMMISSION,  ACTING
PURSUANT TO SAID SECTION 8(A), MAY DETERMINE.
================================================================================

<PAGE>

                             SUBJECT TO COMPLETION,
                               DATED      , 2000


                         SIGNAL PHARMACEUTICALS, INC.


__, 2000
Dear Shareholder:


     The boards of directors of Signal Pharmaceuticals, Inc. and Celgene
Corporation have agreed to merge our companies pursuant to an Agreement and Plan
of Merger dated June 29, 2000 among Signal, Celgene and Celgene Acquisition
Corp., a wholly-owned subsidiary of Celgene. If the merger is completed, Signal
will become a wholly-owned subsidiary of Celgene.

     In the merger, Signal shareholders will receive 0.1257 of a share of
Celgene common stock for each share of Signal common stock that they own
(including shares of Signal preferred stock which will be converted into Signal
common stock immediately before the merger). The common stock of Celgene is
listed on the Nasdaq National Market under the symbol "CELG." On July __, 2000,
the last reported sale price for Celgene common stock was $ per share.

     The merger cannot be completed unless the shareholders of Signal approve
it.

     Signal has scheduled a special meeting for its shareholders to vote on the
merger and on the conversion of the outstanding shares of Signal preferred stock
into shares of Signal common stock. Whether or not you plan to attend this
shareholders' meeting, please take the time to vote on the proposal to be
submitted at the meeting by completing and mailing the enclosed proxy card to
Signal. You may vote at the shareholders' meeting if you own shares of common
stock or preferred stock of Signal as of the close of business on ____________,
2000. The date, time and place of the shareholders' meeting is as follows:

                              ____________, 2000 AT __________
                          SIGNAL PHARMACEUTICALS, INC.
                               5555 OBERLIN DRIVE
                          SAN DIEGO, CALIFORNIA 92121


     This proxy statement/prospectus provides you with detailed information
about the matters to be considered by the Signal shareholders. We encourage you
to read this entire document carefully.

     The board of directors believes that the matters to be presented at the
special meeting are in the best interests of Signal and its shareholders.
Therefore, the board of directors urges shareholders to vote in favor of the
proposals to be presented at the special meeting.
                                                           /s/ John P. Walker
                                                           ---------------------
                                                           John P. Walker
                                                           Chairman of the Board


     YOU SHOULD CAREFULLY CONSIDER THE RISK FACTORS BEGINNING ON PAGE 19 OF THIS
PROXY STATEMENT/PROSPECTUS.

     NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
REGULATOR HAS APPROVED OR DISAPPROVED OF THE SECURITIES TO BE ISSUED IN
CONNECTION WITH THE MERGER OR DETERMINED IF THIS PROXY STATEMENT/PROSPECTUS IS
ACCURATE OR COMPLETE. ANY REPRESENTATION TO THE CONTRARY IS A CRIME.

     This proxy statement/prospectus is dated ______, 2000 and is first being
mailed to shareholders on or about ______, 2000.

     THE INFORMATION IN THIS PROXY STATEMENT/PROSPECTUS IS NOT COMPLETE AND MAY
BE CHANGED. A REGISTRATION STATEMENT RELATING TO THE SECURITIES OFFERED HEREBY
HAS BEEN FILED WITH THE SECURITIES AND EXCHANGE COMMISSION. THIS PROXY
STATEMENT/PROSPECTUS IS NOT AN OFFER TO SELL SECURITIES AND IT IS NOT SOLICITING
AN OFFER TO BUY SECURITIES IN ANY STATE WHERE OFFERS OR SALES ARE NOT PERMITTED.
<PAGE>







--------------------------------------------------------------------------------

     THE PROXY STATEMENT/PROSPECTUS INCORPORATES IMPORTANT BUSINESS AND
FINANCIAL INFORMATION ABOUT CELGENE THAT IS NOT INCLUDED IN OR DELIVERED WITH
THIS DOCUMENT. THIS INFORMATION IS AVAILABLE WITHOUT CHARGE TO SIGNAL
SHAREHOLDERS UPON WRITTEN OR ORAL REQUEST. SHAREHOLDERS SHOULD CONTACT US AT
SIGNAL PHARMACEUTICALS, INC., 5555 OBERLIN DRIVE, SAN DIEGO, CALIFORNIA 92121,
ATTENTION: CORPORATE SECRETARY, OR YOU CAN CALL US AT (858) 558-7500.

     TO OBTAIN TIMELY DELIVERY OF REQUESTED DOCUMENTS BEFORE THE SPECIAL
MEETING, YOU MUST REQUEST THEM NO LATER THAN [ ], WHICH IS FIVE BUSINESS DAYS
BEFORE THE DATE OF THE SPECIAL MEETING.

     ALSO SEE "WHERE YOU CAN FIND MORE INFORMATION" IN THE PROXY
STATEMENT/PROSPECTUS.
--------------------------------------------------------------------------------

<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                               5555 OBERLIN DRIVE
                          SAN DIEGO, CALIFORNIA 92121


                   NOTICE OF SPECIAL MEETING OF SHAREHOLDERS
                       TO BE HELD ON _____________, 2000

To the Shareholders of
Signal Pharmaceuticals, Inc.:

     NOTICE IS HEREBY GIVEN that a Special Meeting of Shareholders of Signal
Pharmaceuticals, Inc., a California corporation, will be held at ____________,
local time, on ________, 2000, at Signal's principal executive offices at 5555
Oberlin Drive, San Diego, California, for the following purposes:

1.  To consider and vote upon a proposal to approve and adopt the Agreement and
    Plan of Merger, dated as of June 29, 2000, by and among Celgene Corporation,
    a Delaware corporation, Celgene Acquisition Corp., a California corporation
    and a wholly-owned subsidiary of Celgene Corporation, and Signal and to
    approve the principal terms of the merger described in the merger agreement.
    The merger agreement provides for the merger of Celgene Acquisition Corp.
    with and into Signal with the result that Signal will become a wholly-owned
    subsidiary of Celgene Corporation. The merger agreement also provides that
    Signal shareholders will receive in the merger 0.1257 of a share of common
    stock, par value $.01 per share, of Celgene Corporation in exchange for each
    share of common stock of Signal that they own (including shares of Signal
    preferred stock which will be converted into Signal common stock immediately
    before the merger). The merger is described more fully in the attached proxy
    statement/prospectus, which includes a copy of the merger agreement.

2.  To consider and vote upon the conversion of all outstanding shares of
    preferred stock of Signal into shares of common stock of Signal effective
    immediately prior to the effective time of the merger. The merger agreement
    provides that the merger will not occur unless all shares of Signal
    preferred stock are converted into shares of Signal common stock immediately
    before the merger.

3.  To consider and act upon such other business and matters or proposals as may
    properly come before the Signal meeting.

     The board of directors of Signal has fixed the close of business on
__________, 2000 as the record date for determining the holders of Signal
capital stock having the right to receive notice of, and to vote at, the Signal
meeting. Only holders of record of Signal capital stock at the close of business
on such date are entitled to notice of, and to vote at, the Signal meeting. A
list of Signal's shareholders entitled to vote at the meeting will be available
during normal business hours at Signal's executive offices for ten days before
the Signal meeting for examination by any Signal shareholder for purposes
germane to the Signal meeting.

     THE BOARD OF DIRECTORS OF SIGNAL UNANIMOUSLY RECOMMENDS THAT YOU VOTE "FOR"
APPROVAL AND ADOPTION OF THE MERGER AGREEMENT, THE PRINCIPAL TERMS OF THE MERGER
AND THE OTHER PROPOSALS PRESENTED AT THE SIGNAL MEETING.

     Approval and adoption of the merger agreement and approval of the principal
terms of the merger require the affirmative vote of the holders of at least a
majority of the outstanding shares of Signal common stock and the affirmative
vote of the holders of at least a majority of the outstanding shares of Signal
preferred stock, each voting as a separate class, entitled to vote at the Signal
meeting. In addition, approval of the conversion of all shares of Signal
preferred stock into Signal common stock requires the affirmative vote of the
holders of at least 75% of the outstanding shares of Signal preferred stock.

     All shareholders are cordially invited to attend the Signal meeting in
person. Whether or not you expect to attend the Signal meeting, please sign and
mail promptly the enclosed proxy that is being solicited on behalf of the board
of directors of Signal. A return envelope that requires no postage if mailed in
the United States is enclosed for that purpose. The proxies of shareholders who
attend the meeting in person may be withdrawn, and such shareholders may vote
personally at the meeting.
<PAGE>

     YOUR VOTE IS VERY IMPORTANT, REGARDLESS OF THE NUMBER OF SHARES YOU OWN.
PLEASE VOTE AS SOON AS POSSIBLE TO MAKE SURE THAT YOUR SHARES ARE REPRESENTED AT
THE MEETING. TO VOTE YOUR SHARES, YOU MAY COMPLETE AND RETURN THE ENCLOSED PROXY
CARD. IF YOU ARE A HOLDER OF RECORD, YOU MAY ALSO CAST YOUR VOTE IN PERSON AT
THE SPECIAL MEETING. IF YOU DO NOT VOTE, IT WILL HAVE THE SAME EFFECT AS VOTING
AGAINST THE MERGER.

                                         Board of Directors

                                        /s/ John P. Walker
                                        ---------------------
                                        John P. Walker
                                        Chairman of the Board

San Diego, California
___________, 2000


                          YOUR VOTE IS IMPORTANT TO US.
               PLEASE COMPLETE, SIGN, DATE AND RETURN YOUR PROXY.
              HOLDERS OF SIGNAL CAPITAL STOCK SHOULD NOT SEND STOCK
                      CERTIFICATES WITH THEIR PROXY CARDS.
<PAGE>

                                TABLE OF CONTENTS


<TABLE>
<CAPTION>
                                                                                            PAGE
                                                                                           -----
<S>                                                                                        <C>
QUESTIONS AND ANSWERS ABOUT THE MERGER
SUMMARY ..................................................................................   1
    The Companies ........................................................................   1
    What Signal Shareholders Will Receive ................................................   1
    The Special Meeting ..................................................................   1
    Our Recommendation to Shareholders ...................................................   2
    Votes Required .......................................................................   2
    The Merger ...........................................................................   3
    Reasons for the Merger ...............................................................   3
    Interests of Signal Officers and Directors in the Merger That Are Different from the
      Interests of Signal Shareholders ...................................................   3
    Conditions to the Merger .............................................................   3
    Termination of the Merger Agreement ..................................................   4
    Dissenters' Rights Available to Signal Shareholders Who Dissent from the Merger ......   4
    Anticipated Accounting Treatment of the Merger .......................................   4
    Regulatory Approvals .................................................................   4
    Listing of the Celgene Common Stock ..................................................   4
    Financial Advisor's Opinion ..........................................................   4
    Treatment of Stock Options and Warrants in the Merger ................................   5
    Tax Consequences .....................................................................   5
    Agreements with Certain Shareholders .................................................   5
    Option Agreement .....................................................................   5
    Agreement of Signal Affiliates .......................................................   5
    Comparative Per Share Information ....................................................   6
    Comparative Per Share Market Price Information .......................................   7
    Forward-Looking Statements May Prove Inaccurate ......................................   8
    Summary of Celgene Selected Consolidated Financial Data ..............................   9
    Summary of Signal Pharmaceuticals, Inc. Selected Financial Data ......................  10
    Unaudited Pro Forma Condensed Combined Financial Statements ..........................  11
    Unaudited Pro Forma Condensed Combined Balance Sheet .................................  12
    Unaudited Pro Forma Condensed Combined Statement of Operations .......................  13
    Notes to Unaudited Pro Forma Condensed Combined Financial Statements .................  17
RISK FACTORS .............................................................................  19
    Risks Relating to the Merger .........................................................  19
    Risks Relating to Celgene ............................................................  20
    Risks Associated with Investing in Celgene Common Stock ..............................  20
    Risks Associated with Investing in the Business of Celgene ...........................  21
    Risks Relating to Investing in the Pharmaceutical Industry ...........................  24
    Risks Relating to Signal's Business ..................................................  26
THE COMPANIES ............................................................................  34
    Celgene Corporation ..................................................................  34
    Signal Pharmaeuticals, Inc. ..........................................................  34
THE SIGNAL SPECIAL MEETING ...............................................................  36
    Date, Time and Place of Special Meeting ..............................................  36
    Matters to be Considered at the Signal Special Meeting ...............................  36
    Signal Board Recommendation ..........................................................  36
</TABLE>

                                        i
<PAGE>

<TABLE>
<CAPTION>
                                                                                            PAGE
                                                                                           -----
<S>                                                                                        <C>
    Votes Required and Outstanding Shares ................................................ 36
    Quorum and Abstention ................................................................ 36
    Voting of Proxies .................................................................... 37
    Revocability of Proxies .............................................................. 37
    Solicitation ......................................................................... 37
    Voting and Proxy Agreements .......................................................... 37
THE MERGER ............................................................................... 38
    General Description of the Merger .................................................... 38
    Background of the Merger ............................................................. 38
    Recommendation of Signal's Board of Directors ........................................ 41
    Signal's Reasons for the Merger ...................................................... 41
    Celgene's Reasons for the Merger ..................................................... 43
    Opinion and Analysis of Signal's Financial Advisor ................................... 44
    Merger Consideration ................................................................. 49
    Stock Options and Warrants ........................................................... 49
    Dissenters' Rights ................................................................... 49
    Effective Time ....................................................................... 50
    Conversion of Shares; Procedures For Exchange of Certificates; No Fractional Shares .. 50
    Nasdaq Listing ....................................................................... 51
    Expenses ............................................................................. 51
    Interests of Certain Persons in the Merger ........................................... 51
    Material Federal Income Tax Consequences ............................................. 51
    Accounting Treatment ................................................................. 54
    Regulatory Approvals ................................................................. 54
    Resale of Celgene Common Stock Following the Merger .................................. 54
THE MERGER AGREEMENT AND RELATED AGREEMENTS .............................................. 55
    General .............................................................................. 55
    Consideration to Be Received in the Merger ........................................... 55
    Conditions to the Merger ............................................................. 55
    Representations and Warranties ....................................................... 56
    Covenants ............................................................................ 58
    Termination .......................................................................... 60
    Amendment; Waiver .................................................................... 61
    Fees and Expenses .................................................................... 61
    Voting and Proxy Agreement ........................................................... 61
    Option Agreement ..................................................................... 61
    Confidentiality Agreement ............................................................ 62
    Agreement of Signal Affiliates ....................................................... 62
INFORMATION REGARDING CELGENE ............................................................ 63
    Management and Additional Information ................................................ 63
INFORMATION REGARDING SIGNAL ............................................................. 63
    Overview of Signal's Business ........................................................ 63
    Management ........................................................................... 77
    Principal Stockholders of Signal ..................................................... 78
    Management's Discussion and Analysis of Financial Condition and Results of Operations  81
    Market Price of and Dividends on Signal's Common Equity and Related Shareholder
      Matters ............................................................................ 85
</TABLE>

                                       ii
<PAGE>


<TABLE>
<CAPTION>
                                                                            PAGE
                                                                        -----
<S>                                                                     <C>
DESCRIPTION OF CELGENE CAPITAL STOCK ..................................  86
    Common Stock ......................................................  86
    Preferred Stock ...................................................  86
    Shareholder Rights Plan ...........................................  86
    Delaware Law and Selected By-Law Provisions .......................  87
    Transfer Agent and Registrar ......................................  87
COMPARATIVE RIGHTS OF CELGENE STOCKHOLDERS AND SIGNAL
 SHAREHOLDERS .........................................................  87
    Size of the Board of Directors ....................................  88
    Elimination of Cumulative Voting ..................................  88
    Removal of Directors ..............................................  88
    Filling New Seats or Vacancies on the Board of Directors ..........  89
    Indemnification and Limitation of Liability .......................  89
    Interested Director Transactions ..................................  90
    Loans to Officers and Employees ...................................  90
    Stockholder Derivative Suits ......................................  91
    Elimination of Actions by Written Consent of Stockholders .........  91
    Power to Call Special Meetings of Stockholders ....................  91
    Stockholder Approval of Certain Business Combinations .............  91
    Mergers ...........................................................  92
    Dissenters' Rights ................................................  93
OTHER MATTERS .........................................................  93
LEGAL MATTERS .........................................................  94
EXPERTS ...............................................................  94
WHERE YOU CAN FIND MORE INFORMATION ...................................  94
FORWARD-LOOKING STATEMENTS ............................................  95
APPENDIX A  Agreement and Plan of Merger
    Exhibit  A-1 Form of Voting and Proxy  Agreement
    Exhibit  A-2 Form of Option Agreement
    Exhibits B-1 and B-2 Form of Tax  Representation  Letters
    Exhibit  C Form of  Affiliate  Agreement
    Exhibit  D Form of Legal  Opinion  of  Cooley Godward LLP
    Exhibit  E Form of Tax Opinion of Proskauer Rose LLP
    Exhibit  F Form of Legal  Opinion of  Proskauer  Rose LLP
    Exhibit  G Form of Tax  Opinion of Cooley Godward LLP
APPENDIX B California General Corporation Law--Dissenters' Rights
APPENDIX C Opinion of FleetBoston Robertson Stephens Inc.
INDEX TO SIGNAL FINANCIAL STATEMENTS ..................................  F-1
</TABLE>

                                       iii
<PAGE>
                     QUESTIONS AND ANSWERS ABOUT THE MERGER

Q: WHY ARE THE TWO COMPANIES PROPOSING TO MERGE?

     A: We believe that the merger of Celgene and Signal will create a stronger,
more competitive company capable of achieving greater financial strength,
operational efficiencies, technology development, earning power and growth
potential than either company would have on its own.


Q: WHAT WILL I RECEIVE IN THE MERGER?

     A: As a result of the merger, Signal shareholders will receive 0.1257 of a
share of common stock, par value $.01 per share, of Celgene Corporation in
exchange for each share of common stock of Signal that they own (including
shares of Signal preferred stock which will be converted into Signal common
stock immediately before the merger). For example, if you own 1,000 shares of
Signal common stock, you will receive 125 shares of Celgene common stock in
exchange for your Signal shares. No fractional shares of Celgene common stock
will be issued; instead, you will receive cash for the fraction of a share of
Celgene common stock you would have otherwise received.


Q:  WHAT  PERCENTAGE OF THE OUTSTANDING COMMON STOCK OF CELGENE WOULD BE HELD BY
SIGNAL SHAREHOLDERS?

     A: Signal shareholders would hold approximately 5.3% of the outstanding
common stock of Celgene immediately after the merger.


Q: WHEN DO YOU EXPECT THE MERGER TO BE COMPLETED?

     A: We hope to complete the merger within two business days after the day on
which all the conditions set forth in the merger agreement are either satisfied
or waived.


Q: WHAT DO I NEED TO DO NOW?

     A: After carefully reading and considering the information contained in
this document and its appendices, indicate on your proxy card how you want to
vote, and sign and mail the proxy card in the enclosed return envelope as soon
as possible, so that your shares may be represented at the special meeting. If
you sign and send in your proxy card and do not indicate how you want to vote,
we will count your proxy card as a vote in favor of the proposals to be voted
upon at your special meeting. If you do not vote or you abstain, it will have
the effect of a vote against the proposal or proposals presented to the special
meeting. The board of directors of Signal recommends voting in favor of the
merger agreement and the merger, and in favor of the conversion of all
outstanding shares of Signal preferred stock into shares of Signal common stock
immediately before the merger.


Q: WHAT IS THE REQUIRED VOTE TO APPROVE THE MERGER?

     A: Approval and adoption of the merger agreement and approval of the
principal terms of the merger requires the affirmative vote of the holders of at
least a majority of the outstanding shares of Signal common stock and the
affirmative vote of the holders of at least a majority of the outstanding shares
of Signal preferred stock, each voting as a separate class, entitled to vote at
the Signal meeting. Celgene has entered into agreements with certain of the
shareholders of Signal pursuant to which these Signal shareholders have granted
to Celgene an irrevocable proxy to vote all of their shares of Signal capital
stock in favor of the approval and adoption of the merger agreement, approval of
the principal terms of the merger and conversion of the outstanding shares of
preferred stock into shares of common stock. As of the record date, these
shareholders owned shares representing approximately 56% of the outstanding
shares of Signal common stock and approximately 79% of Signal preferred stock
entitled to vote at the Signal special meeting. Accordingly, Celgene has
sufficient voting power to constitute a quorum and to approve all matters to be
considered at the Signal shareholders' meeting. Celgene has agreed to vote all
shares of Signal company stock and Signal preferred stock subject to these
agreements in favor of the merger proposal and the preferred stock conversion
proposal.
<PAGE>

Q:  WHAT  IS  THE  REQUIRED  VOTE  TO APPROVE THE CONVERSION OF SIGNAL PREFERRED
    STOCK?

     A: Approval of the conversion of all outstanding shares of Signal preferred
stock into shares of Signal common stock requires the affirmative vote of the
holders of at least 75% of the outstanding shares of Signal preferred stock. The
merger agreement provides that the merger will not occur unless all shares of
Signal preferred stock are converted into shares of Signal common stock
immediately before the merger. Celgene has entered into agreements with certain
shareholders of Signal pursuant to which these Signal shareholders have granted
to Celgene an irrevocable proxy to vote all of their preferred shares of Signal
stock in favor of the conversion of preferred stock. As of the record date,
these shareholders owned shares representing approximately 79% of Signal
preferred stock entitled to vote at the Signal special meeting. Accordingly,
Celgene has sufficient voting power to constitute a quorum and to approve all
matters to be considered at the Signal shareholders' meeting. Celgene has agreed
to vote all shares of Signal common stock and Signal preferred stock subject to
those agreements in favor of the merger proposal and the preferred stock
conversion proposal.


Q:  IF  I  AM  NOT  GOING  TO ATTEND THE SHAREHOLDER MEETING, SHOULD I RETURN MY
    PROXY CARD INSTEAD?

     A: Yes. Please fill out your proxy card and mail it to us in the enclosed
return envelope as soon as possible. Returning your proxy card ensures that your
shares will be represented at the special meeting.


Q: WHAT HAPPENS IF I DO NOT RETURN A PROXY CARD?

     A: If you are a Signal shareholder, the failure to return your proxy card
will have the same effect as voting against the merger.


Q: MAY I VOTE IN PERSON?

     A: Yes. You may attend the special meeting of Signal shareholders and vote
your shares in person rather than signing and returning your proxy card.


Q: WHAT DO I DO IF I WANT TO CHANGE MY VOTE?

     A: You should send in a new, later dated, signed proxy card to Signal's
corporate secretary before the special meeting or attend the special meeting in
person and vote.


Q: SHOULD I SEND IN MY STOCK CERTIFICATES NOW?

     A: No. After the merger is completed, we will send Signal shareholders
written instructions for exchanging their stock certificates.


Q: AM I ENTITLED TO DISSENTERS' RIGHTS?

     A: Signal shareholders will be entitled to dissenters' rights in certain
instances.


Q: WHAT ARE THE TAX CONSEQUENCES TO SHAREHOLDERS OF THE MERGER?

     A: The merger will not be a taxable event for federal income tax purposes
for Signal shareholders. Tax matters, however, are very complicated, and the tax
consequences of the merger to you will depend on the facts of your particular
situation. We encourage you to contact your tax advisors to determine the tax
consequences of the merger to you. To review the tax consequences to Signal
shareholders in greater detail, see pages 51 to 54 of this proxy
statement/prospectus.


Q: WHO CAN HELP ANSWER MY QUESTIONS?

     A: If you would like additional copies of this proxy statement/prospectus
or if you have questions about the merger, you can contact us at Signal
Pharmaceuticals, Inc., 5555 Oberlin Drive, San Diego, California 92121,
Attention: Corporate Secretary.
<PAGE>

                                     SUMMARY

This summary highlights selected information from this proxy
statement/prospectus and may not contain all of the information that is
important to you. In order to fully understand the merger and related
transactions and for a more complete description of the legal terms of the
merger and related transactions, you should read carefully this entire document
and the documents to which you are referred. See "Where You Can Find More
Information" on page 94. The merger agreement is attached as Appendix A to this
proxy statement/prospectus. We encourage you to read the merger agreement as it
is the legal document that governs the merger.


                                  THE COMPANIES


SIGNAL PHARMACEUTICALS, INC.
5555 Oberlin Drive
San Diego, California 92121
(858) 558-7500

Signal Pharmaceuticals, Inc., a California corporation, is a biopharmaceutical
company focused on discovering and developing new classes of small molecule
drugs that regulate disease-associated genes. After the merger, Signal will be a
wholly-owned subsidiary of Celgene. Signal's principal executive offices will
continue to be located at 5555 Oberlin Drive, San Diego, California 92121.


CELGENE CORPORATION
7 Powder Horn Drive
Warren, New Jersey 07059
(732) 271-1001

Celgene Corporation, a Delaware corporation, is an independent biopharmaceutical
company engaged in the discovery, development and commercialization of small
molecule drugs for the treatment of cancer and immunological diseases. Celgene's
primary therapeutic focus is on the development of orally adminstered, small
molecule pharmaceuticals that regulate tumor necrosis factor alpha, or TNF-, and
are anti-angiogenic. TNF- has been linked to the cause and symptoms of many
chronic inflammatory and immunological diseases. Anti-angiogenic drugs inhibit
the growth of undesirable blood vessels, including those that promote tumor
growth.


                      WHAT SIGNAL SHAREHOLDERS WILL RECEIVE

Upon consummation of the merger, shareholders of Signal will receive 0.1257 of a
share of common stock, par value $.01 per share, of Celgene in exchange for each
share of common stock of Signal that they own (including shares of Signal
preferred stock which will be converted into Signal common stock immediately
before the merger). No fractional shares of Celgene common stock will be issued
in the merger; instead, Signal shareholders will receive cash for the fraction
of a share of Celgene common stock they would have otherwise received.


                               THE SPECIAL MEETING

The special meeting of shareholders of Signal will be held at ______, local
time, on ______, 2000, at Signal's executive office at 5555 Oberlin Drive, San
Diego, California. At the meeting, holders of Signal capital stock will consider
and vote upon:

o  a proposal to approve and adopt the merger agreement and approve the
   principal terms of the merger;

                                        1
<PAGE>

o  a proposal to approve the conversion of all outstanding shares of Signal
   preferred stock into shares of Signal common stock, effective immediately
   before the merger; and

o  any other matters that may properly come before the meeting.


                       OUR RECOMMENDATION TO SHAREHOLDERS

The Signal board of directors believes that the merger is in the best interests
of its shareholders and recommends that the Signal shareholders vote "FOR" the
proposal to approve and adopt the merger agreement and approve the principal
terms of the merger and "FOR" the proposal to convert outstanding shares of
preferred stock into shares of common stock.


                                 VOTES REQUIRED

Approval and adoption of the merger agreement and approval of the principal
terms of the merger require the affirmative vote of the holders of a majority of
the outstanding shares of Signal common stock and the affirmative vote of the
holders of a majority of the outstanding shares of Signal preferred stock, each
voting as a separate class, entitled to vote at the Signal meeting. In addition,
approval of the conversion of all shares of Signal preferred stock into Signal
common stock requires the affirmative vote of the holders of at least 75% of the
outstanding shares of Signal preferred stock. Celgene has entered into
agreements with certain shareholders of Signal pursuant to which these Signal
shareholders have granted to Celgene an irrevocable proxy to vote all of their
shares of Signal capital stock in favor of the approval and adoption of the
merger agreement and approval of the principal terms of the merger and, where
applicable, in favor of the conversion of preferred stock. As of the record
date, these shareholders owned shares representing approximately 56% of the
outstanding shares of Signal common stock and approximately 79% of Signal
preferred stock entitled to vote at the Signal special meeting. Accordingly,
Celgene has sufficient voting power to constitute a quorum and to approve all
matters to be considered at the Signal shareholders' meeting. Celgene has agreed
to vote all shares of Signal common stock and Signal preferred stock subject to
those agreements in favor of the merger proposal and the preferred stock
conversion proposal. As of the record date, Signal directors and executive
officers and their affiliates owned approximately 6,853,825 shares of Signal
capital stock which represented approximately 23% of the outstanding shares of
Signal capital stock entitled to vote at the Signal special meeting.

PROCEDURES FOR VOTING YOUR SHARES. You may vote your shares by signing your
proxy card and mailing it in the enclosed return envelope. If you are a holder
of record, you may vote in person at the special meeting. If you do not include
instructions on how to vote your properly executed proxy card, your shares will
be voted FOR approval and adoption of the merger agreement, approval of the
principal terms of the merger and conversion of the outstanding shares of
preferred stock into shares of common stock. If you do not vote, it will have
the same effect as voting against the merger.

PROCEDURE FOR CHANGING YOUR VOTE. You can change your vote at any time before
your proxy is voted at the special meeting. You can do this in one of three
ways. First, you can send a written notice stating that you are revoking your
proxy. Second, you can complete and submit a new proxy card. If you choose
either of these two methods, you must submit your notice of revocation of your
new proxy to the Secretary of Signal. Third, if you are a holder of record, you
can attend the special meeting and vote in person.


                                        2
<PAGE>
                                   THE MERGER

The merger agreement is attached as Appendix A to this proxy
statement/prospectus. We encourage you to read the merger agreement because it
is the legal document that governs the merger.

The merger agreement provides that, upon consummation of the merger, Celgene
Acquisition Corp. will merge with and into Signal. Signal will continue as the
surviving corporation and become a wholly-owned subsidiary of Celgene. The
merger will become effective upon the filing of an agreement of merger with the
Secretary of State of the State of California, or such other time as the parties
may specify. This filing is anticipated to be made two business days after
receipt of Signal shareholder approval and all required regulatory approvals and
the satisfaction or waiver of the other conditions to the merger.


                             REASONS FOR THE MERGER


Celgene

o strengthen research

o diversify pipeline

o accelerate discovery and development


Signal

Signal's board of directors determined that the proposed merger is in the best
interests of Signal and its shareholders based on a number of factors, including
the following:

     o greater financial security and leverage leading to an enhanced
       negotiating position with potential partners or licenses;

     o the existence of a public market for the Celgene common stock;

     o the strategic fit between Signal and Celgene; and

     o the financial consideration to be received by Signal's shareholders.


       INTERESTS OF SIGNAL OFFICERS AND DIRECTORS IN THE MERGER THAT ARE
              DIFFERENT FROM THE INTERESTS OF SIGNAL SHAREHOLDERS

As of the record date, Signal directors and executive officers and their
affiliates owned 6,853,825 shares of Signal capital stock, which represented
approximately 23% of the outstanding shares of Signal capital stock entitled to
vote at the Signal special meeting. Pursuant to the merger agreement, Signal's
directors and executive officers will receive the same consideration for their
shares of Signal common stock as the other Signal shareholders. In addition, as
part of the merger, Alan Lewis, Signal's president and chief executive officer,
is negotiating an employment agreement with Celgene to be effective upon the
consummation of the merger.


                            CONDITIONS TO THE MERGER

The obligations of Celgene and Signal to complete the merger are subject to the
satisfaction of conditions described below.


                                        3
<PAGE>

                       TERMINATION OF THE MERGER AGREEMENT

Celgene and Signal can terminate the merger agreement by mutual written consent
and for various other reasons described below. The merger agreement provides
that if Signal's board withdraws its recommendation that shareholders vote for
the merger or solicits or recommends another acquisition transaction with a
third party, Signal will be required to pay Celgene a termination fee of
$10,000,000. If the merger is not completed by December 31, 2000 and Celgene
terminates the merger agreement, or if Signal shareholders do not approve the
merger, then Signal will also be required to pay Celgene a termination fee of
$10,000,000 if Signal signs or completes another acquisition transaction with a
third party within one year. In addition, if Signal or Celgene terminates the
merger agreement because of any material breach by the other of any
representation, warranty or covenant under the merger agreement, the breaching
party will be required to pay the other party $5,000,000. Signal would be
entitled to credit this payment against any termination fee owed to Celgene.


              DISSENTERS' RIGHTS AVAILABLE TO SIGNAL SHAREHOLDERS
                           WHO DISSENT FROM THE MERGER

Signal shareholders will be entitled to dissenters' rights in some instances as
described below.


                ANTICIPATED ACCOUNTING TREATMENT OF THE MERGER

The merger is intended to qualify as a pooling-of-interests. The
pooling-of-interests method of accounting assumes the companies had always been
combined, and the historical financial statements for periods prior to closing
of the merger are restated as though the companies had always been combined as
required under United States generally accepted accounting principles. The
assets and liabilities of Celgene and Signal will be carried forward by the
combined company at their historical recorded amounts.


                              REGULATORY APPROVALS

The Hart-Scott-Rodino Antitrust Improvements Act prohibits us from completing
the merger until we have furnished certain information and materials to the
Antitrust Division of the Department of Justice and the Federal Trade Commission
and the required waiting period has ended. On July 11, 2000, Celgene and Signal
each filed the required notification and report forms. The required waiting
period expires on August 10, 2000 unless extended or terminated earlier.


                       LISTING OF THE CELGENE COMMON STOCK

Celgene will use its reasonable best efforts to cause the shares of Celgene
common stock to be issued in connection with the merger to be approved for
quotation on the Nasdaq National Market or listed on such securities exchange as
Celgene common stock is then listed, subject to official notice of issuance.


                           FINANCIAL ADVISOR'S OPINION

Signal has received the opinion of FleetBoston Robertson Stephens Inc., dated
June 28, 2000, that as of the date of the opinion, and subject to and based on
the assumptions, limitations and qualifications referred to in the opinion, the
exchange ratio of 0.1257 of a share of Celgene common stock for each share of
Signal common stock was fair to the holders of Signal common stock from a
financial point of view. A copy of this opinion is attached as Appendix C. See
also "Opinion and Analysis of Signal's Financial Advisor."


                                        4
<PAGE>

             TREATMENT OF STOCK OPTIONS AND WARRANTS IN THE MERGER

Under the merger agreement, each option and warrant to purchase Signal common
stock or Series C-1 or Series C-2 preferred stock outstanding immediately prior
to the effective time of the merger, whether vested or unvested, will cease to
represent a right to acquire shares of Signal common stock or Series C-1 or
Series C-2 preferred stock and will be converted, at the effective time of the
merger, into an option or warrant to acquire, on the same terms and conditions,
the number of shares of Celgene common stock determined by multiplying the
number of shares of Signal common stock or Series C-1 or Series C-2 preferred
stock subject to that Signal stock option or warrant by 0.1257, rounded down, if
necessary, to the nearest whole share. The exercise price of these stock options
will be the exercise price for the stock option or warrant immediately prior to
the effective time of the merger divided by 0.1257, rounded up to the nearest
cent.


                                TAX CONSEQUENCES

You generally will not recognize income, gain or loss upon the exchange of the
Signal capital stock for Celgene common stock (including a fractional share for
which cash is received). Your tax basis in Celgene common stock received upon
the exchange should generally be equal to your tax basis in the Signal common
stock exchanged. We encourage you to consult your tax advisor regarding the tax
consequences of the merger for your particular circumstances.


                      AGREEMENTS WITH CERTAIN SHAREHOLDERS

Celgene has entered into agreements with certain shareholders of Signal pursuant
to which these Signal shareholders have granted to Celgene an irrevocable proxy
to vote all of their shares of Signal capital stock in favor of the approval and
adoption of the merger agreement and approval of the principal terms of the
merger and, where applicable, in favor of the conversion of preferred stock. As
of the record date, these shareholders owned shares representing approximately
56% of the outstanding shares of Signal common stock and approximately 79% of
Signal preferred stock entitled to vote at the Signal special meeting. The
shareholders agreement provides that it will terminate upon the earlier of the
completion of the merger and the termination of the merger agreement in
accordance with its terms.


                                OPTION AGREEMENT

In connection with the merger agreement, Signal entered into an option agreement
with Celgene in which Signal granted Celgene an option to purchase 2,000,000
shares of Signal common stock and stock appreciation rights with respect to
3,000,000 shares of Signal common stock for a cash exercise price of $6.60 per
share, subject to adjustment as described in the option agreement. The option
agreement provides that Celgene can exercise the option upon the happening of
events as described elsewhere in this proxy statement/prospectus.


                         AGREEMENT OF SIGNAL AFFILIATES

Rule 145 under the Securities Act of 1933 regulates the disposition of
securities of "affiliates" of Signal in connection with the merger. Signal has
agreed to use its reasonable best efforts to cause each person who is identified
as an affiliate of Signal to deliver to Celgene, before the effective time of
the merger, a written affiliate agreement. Under these affiliate agreements,
each affiliate will represent that he, she or it has been advised that the
affiliate may not sell, transfer or otherwise dispose of Celgene common stock
issued to the affiliate in the merger unless the sale, transfer or other
disposition complies with certain conditions described elsewhere in this proxy
statement/prospectus.


                                        5
<PAGE>

                        COMPARATIVE PER SHARE INFORMATION

The following table sets forth selected historical per share information of
Celgene and Signal and unaudited pro forma combined per share information after
giving effect to the merger between Celgene and Signal, under the
pooling-of-interests method of accounting, as if the companies have been
combined for all periods presented. You should read this information in
conjunction with the selected historical audited and unaudited financial
information, included elsewhere in this document, and the historical audited
financial statements of Celgene and Signal and related notes that are included
in this proxy statement/prospectus or incorporated in this document by
reference. The unaudited pro forma combined per share information is derived
from, and should be read in conjunction with, the unaudited pro forma condensed
combined financial statements and related notes included elsewhere in this proxy
statement/prospectus. Unaudited Pro Forma Signal Per Share Equivalents are
calculated by multiplying the corresponding Unaudited Pro Forma Combined per
share amounts by the exchange ratio of 0.1257.

The unaudited pro forma combined per share information does not purport to
represent what the actual financial position or results of operations of Celgene
and Signal would have been had the companies been combined for the periods
presented or to project Celgene's and Signal's financial position or results of
operations for any future date or period.

<TABLE>
<CAPTION>
                                                                    THREE MONTHS               FOR THE YEARS ENDED
                                                                  ENDED MARCH 31,                 DECEMBER 31,
                                                                 -----------------   ---------------------------------------
                                                                        2000             1999          1998          1997
                                                                 -----------------   -----------   -----------   -----------
                                                                    (UNAUDITED)
<S>                                                              <C>                 <C>           <C>           <C>
UNAUDITED PRO FORMA COMBINED
Per common share-basic and diluted:
 Loss from continuing operations
   applicable to common stockholders .........................        $ (0.11)         $ (0.59)      $ (0.75)      $ (0.87)
 Book value (deficit) at end of period (5)....................           3.93            (0.18)
CELGENE -- HISTORICAL (1) Per common share-basic and diluted:
 Loss from continuing operations
   applicable to common stockholders .........................          (0.05)           (0.43)        (0.66)        (0.72)
 Unaudited book value (deficit) at end of period (3) .........           4.22            (0.30)
SIGNAL -- HISTORICAL Per common share-basic and diluted:
 Loss from continuing operations
   applicable to common stockholders .........................          (0.98)           (2.64)        (1.65)        (2.82)
 Unaudited book value (deficit) at end of period (3) .........          (8.42)           (9.72)
UNAUDITED PRO FORMA SIGNAL PER SHARE
 EQUIVALENTS(2)
Per common share-basic and diluted:
 Loss from continuing operations
   applicable to common stockholders .........................          (0.01)           (0.07)        (0.09)        (0.11)
 Book value (deficit) at end of period (5) ...................           0.49            (0.02)
UNAUDITED PRO FORMA COMBINED ASSUMING CONVERSION OF SIGNAL
PREFERRED STOCK TO COMMON STOCK (4)
Per common share-basic and diluted:
 Loss from continuing operations
  applicable to common stockholders...........................          (0.11)           (0.56)

</TABLE>

-----------

(1) Amounts reflect a three-for-one stock split declared by Celgene and issued
    on April 14, 2000.
(2) Amounts are calculated by multiplying the corresponding unaudited pro forma
    combined per share amounts by the exchange ratio in the merger of 0.1257 of
    a share of Celgene common stock for each share of Signal common stock.
(3) Amounts are calculated by dividing the corresponding stockholders' equity
    less any preferred stock liquidation preference by the corresponding common
    shares outstanding.
(4) Amounts are  calculated  assuming  conversion of Signal  preferred  stock to
    common stock as of January 1, 1999 or the date of issuance of such preferred
    stock, if later.
(5) Amounts are calculated by dividing the corresponding stockholders' equity by
    the corresponding common shares outstanding assuming conversion of Signal
    preferred stock to common stock.

Note:  No cash dividends were paid by Celgene or Signal during any of the
       periods presented.

                                        6
<PAGE>
                 COMPARATIVE PER SHARE MARKET PRICE INFORMATION

Celgene's common stock is traded on the Nasdaq National Market under the symbol
"CELG". The following table sets forth, for the periods indicated, the intra-day
high and low sale prices per share of common stock on the Nasdaq National
Market:

<TABLE>
<CAPTION>
                                                      HIGH*          LOW*
                                                  ------------   ------------
<S>                                               <C>            <C>
2000
Third Quarter (through July 20, 2000) .........    $  58.750      $  44.500
Second Quarter ................................       68.500         25.000
First Quarter .................................       62.333         18.917
1999
Fourth Quarter ................................    $  24.208      $   8.646
Third Quarter .................................        9.667          4.875
Second Quarter ................................        6.688          5.133
First Quarter .................................        6.208          3.833
1998
Fourth Quarter ................................    $   5.750      $   2.563
Third Quarter .................................        5.000          1.750
Second Quarter ................................        3.833          3.000
First Quarter .................................        3.875          2.354
</TABLE>

* The stock prices have been adjusted to reflect a three-for-one stock split
  declared by Celgene and issued on April 14, 2000.

On June 29, 2000, the last trading day before the public announcement of the
proposed acquisition of Signal, the last reported sales price per share of
Celgene common stock was $53.50. On July 25, 2000, the last trading day before
the date of this proxy statement/prospectus, the last reported sales price per
share of Celgene common stock was $44.75. Because the securities of Signal are
not publicly traded, they have no readily ascertainable market value.

Because the market price of Celgene common stock is subject to fluctuation, the
market value of the shares of Celgene common stock that holders of Signal
capital stock will be entitled to receive pursuant to the merger may increase or
decrease prior to and following the merger. The exchange ratio is fixed and will
not be adjusted to compensate Signal's shareholders for decreases in the market
price of Celgene common stock which could occur prior to the merger becoming
effective. WE URGE SHAREHOLDERS TO OBTAIN CURRENT MARKET QUOTATIONS FOR CELGENE
COMMON STOCK. WE CANNOT ASSURE YOU AS TO THE FUTURE PRICES OR MARKETS FOR
CELGENE COMMON STOCK.

Neither Celgene nor Signal has paid any cash dividends in the past. Both Celgene
and Signal intend to retain future earnings, if any, to fund the development and
growth of their businesses and do not anticipate paying cash dividends in the
foreseeable future.


                                        7
<PAGE>

                FORWARD-LOOKING STATEMENTS MAY PROVE INACCURATE

Each of Signal and Celgene has made forward-looking statements in this proxy
statement/prospectus, and in documents that are incorporated by reference in
this proxy statement/prospectus, that are subject to risks and uncertainties.
All statements included or incorporated by reference in this proxy
statement/prospectus or made by management of Celgene or Signal other than
statements of historical fact regarding Celgene, Signal or the combined company
are forward-looking statements. Examples of forward-looking statements include
statements regarding Celgene's, Signal's or the combined company's future
financial results, operating results, product successes, business strategies,
projected costs, future products, competitive positions and plans and objectives
of management for future operations. In some cases, you can identify
forward-looking statements by terminology, such as "may," "will," "should,"
"would," "expects," "plans," "anticipates," "believes," "estimates," "predicts,"
"potential," or "continue" or the negative of these terms or other comparable
terminology. Any expectations based on these forward-looking statements are
subject to risks and uncertainties and other important factors, including those
discussed in the "Risk Factors" section of this proxy statement/prospectus.
These and many other factors could affect the future financial and operating
results of Celgene, Signal or the combined company. These factors could cause
actual results to differ materially from expectations based on forward-looking
statements made in this document or elsewhere by or on behalf of Celgene, Signal
or the combined company.

                                        8
<PAGE>

            SUMMARY OF CELGENE SELECTED CONSOLIDATED FINANCIAL DATA

The following selected consolidated financial information of Celgene and
subsidiary is provided to aid your analysis of the financial aspects of the
merger. We derived this information from audited consolidated financial
statements for the years ended December 31, 1995 through 1999 and from unaudited
consolidated financial statements for the three months ended March 31, 2000 and
March 31, 1999. This information is only a summary, and you should read it in
conjunction with Celgene's historical consolidated financial statements and
related notes and Management's Discussion and Analysis of Financial Condition
and Results of Operations contained in the annual reports, quarterly reports and
other information on file with the Securities and Exchange Commission. See
"Where You Can Find More Information" on page 94.

<TABLE>
<CAPTION>
                                                    THREE MONTHS
                                                       ENDED
                                                     MARCH 31,
                                              ------------------------
                                                  2000         1999
                                              ------------ -----------
In thousands, except per share data                 (UNAUDITED)
<S>                                           <C>          <C>
CONSOLIDATED STATEMENTS OF
 OPERATIONS DATA:
Net revenues ................................   $ 11,866    $  4,304
Costs and operating expenses ................     16,546      10,496
Interest income/(expense), net ..............      1,536        (400)
Tax benefit .................................         --          --
                                                --------    --------
Loss from continuing operations .............     (3,144)     (6,592)
 Preferred stock dividend (including
  accretion and imputed dividends) ..........         --          --
                                                --------    --------
Loss from continuing operations
 applicable to common stockholders ..........   $ (3,144)   $ (6,592)
                                                ========    ========
Per share basic and diluted:
 Loss from continuing operations
  applicable to common stockholders .........   $  (0.05)   $  (0.13)
                                                ========    ========

<CAPTION>
                                                                  YEAR ENDED DECEMBER 31,
                                              ---------------------------------------------------------------
                                                  1999         1998         1997         1996         1995
                                              ------------ ------------ ------------ ------------ -----------
In thousands, except per share data
<S>                                           <C>          <C>          <C>          <C>          <C>
CONSOLIDATED STATEMENTS OF
 OPERATIONS DATA:
Net revenues ................................  $  26,210    $   3,801    $   1,122    $     882    $    472
Costs and operating expenses ................     48,865       36,273       26,526       18,924       8,982
Interest income/(expense), net ..............     (2,144)         449          384          984         143
Tax benefit .................................      3,018           --           --           --          --
                                               ---------    ---------    ---------    ---------    --------
Loss from continuing operations .............    (21,781)     (32,023)     (25,020)     (17,058)     (8,367)
 Preferred stock dividend (including
  accretion and imputed dividends) ..........         --           25        1,474        3,791          --
                                               ---------    ---------    ---------    ---------    --------
Loss from continuing operations
 applicable to common stockholders ..........  $ (21,781)   $ (32,048)   $ (26,494)   $ (20,849)   $ (8,367)
                                               =========    =========    =========    =========    ========
Per share basic and diluted:
 Loss from continuing operations
  applicable to common stockholders .........  $   (0.43)   $   (0.66)   $   (0.72)   $   (0.73)   $  (0.35)
                                               =========    =========    =========    =========    ========

</TABLE>


<TABLE>
<CAPTION>
                                                                               DECEMBER 31,
                                                    -------------------------------------------------------------------
                                         MARCH 31,
                                            2000         1999          1998          1997         1996         1995
                                         ---------- ------------- ------------- ------------- ------------ ------------
                                         (UNAUDITED
In thousands                                 D)
<S>                                      <C>   <C>  <C>           <C>           <C>           <C>          <C>
CONSOLIDATED BALANCE
 SHEET DATA:
Cash and cash equivalents, and
 marketable securities ................. $292,365    $   19,527    $    5,124    $   13,583    $  17,815    $  11,713
Total assets ........................... 307,165         32,334        11,928        18,217       20,938       14,211
Convertible debentures ................. --                  --            --            --        2,026        4,592
Convertible notes ...................... 29,243          38,495         8,349            --           --           --
Accumulated deficit .................... (169,588)     (166,394)     (144,613)     (119,521)     (92,599)     (70,989)
Stockholders' equity (deficit) ......... 271,123        (15,709)       (3,733)       15,425       16,065        7,143
</TABLE>

                                        9
<PAGE>

        SUMMARY OF SIGNAL PHARMACEUTICALS, INC. SELECTED FINANCIAL DATA

     The following selected financial information of Signal Pharmaceuticals is
provided to aid your analysis of the financial aspects of the merger. We derived
this information from audited financial statements for the years ended December
31, 1995 through 1999 and from unaudited financial statements for the three
months ended March 31, 2000 and March 31, 1999. This information is only a
summary, and you should read it in conjunction with the Signal Pharmaceuticals,
Inc. historical financial statements and related notes which are included
herein.

<TABLE>
<CAPTION>
                                                 THREE MONTHS
                                                     ENDED
                                                   MARCH 31,
                                          ---------------------------
                                               2000          1999
                                          ------------- -------------
In thousands, except per share data               (UNAUDITED)
<S>                                       <C>           <C>
STATEMENTS OF OPERATIONS
 DATA:
 Net revenues ...........................   $   2,671     $   2,923
 Operating expenses .....................       6,204         5,155
 Interest income/(expense), net .........          53            18
                                            ---------     ---------
 Net loss ...............................      (3,480)       (2,214)
 Preferred stock dividend
  (including accretion and
  imputed dividends) ....................          --            --
                                            ---------     ---------
 Net loss applicable to common
  stockholders ..........................   $  (3,480)    $  (2,214)
                                            =========     =========
 Net loss per share applicable to
  common stockholders-basic and
  diluted ...............................   $   (0.98)    $   (0.71)
                                            =========     =========


<CAPTION>
                                                                 YEAR ENDED DECEMBER 31,
                                          ---------------------------------------------------------------------
                                               1999          1998          1997          1996          1995
                                          ------------- ------------- ------------- ------------- -------------
In thousands, except per share data
<S>                                       <C>           <C>           <C>           <C>           <C>
STATEMENTS OF OPERATIONS
 DATA:
 Net revenues ...........................   $  11,748     $  15,414     $   7,579     $   3,933     $     299
 Operating expenses .....................      19,758        20,371        13,128        10,195         7,110
 Interest income/(expense), net .........         154           601          (191)           53           329
                                            ---------     ---------     ---------     ---------     ---------
 Net loss ...............................      (7,856)       (4,356)       (5,740)       (6,209)       (6,482)
 Preferred stock dividend
  (including accretion and
  imputed dividends) ....................         818            --            --            --            --
                                            ---------     ---------     ---------     ---------     ---------
 Net loss applicable to common
  stockholders ..........................   $  (8,674)    $  (4,356)    $  (5,740)    $  (6,209)    $  (6,482)
                                            =========     =========     =========     =========     =========
 Net loss per share applicable to
  common stockholders-basic and
  diluted ...............................   $   (2.64)    $   (1.65)    $   (2.82)    $   (3.69)    $   (4.56)
                                            =========     =========     =========     =========     =========

</TABLE>


<TABLE>
<CAPTION>
                                                                                   DECEMBER 31,
                                                      ----------------------------------------------------------------------
                                           MARCH 31,
                                             2000            1999           1998          1997          1996           1995
                                         ----------      ------------   -----------   -----------   ------------   ------------
In thousands                              (UNAUDITED)
<S>                                      <C>          <C>            <C>           <C>           <C>            <C>
BALANCE SHEET DATA:
 Cash and cash equivalents,
  and short-term investments .........   $ 6,337       $   9,420      $  12,952     $  20,866     $   5,460      $   4,211
 Total assets ........................   11,650           14,539         19,558        23,838         9,047          6,866
 Long-term obligations under
  capital leases and
  equipment notes payable ............   1,570             1,805          2,111         1,548         2,746            513
 Accumulated deficit .................   (41,257)        (37,776)       (29,102)      (24,745)      (19,005)       (12,796)
 Stockholders' equity ................   3,411             5,983         12,125        15,164         1,512          5,574

</TABLE>


                                       10
<PAGE>

          UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

The following unaudited pro forma condensed combined financial statements have
been prepared to give effect to the merger, using the pooling-of-interests
method of accounting.

The pro forma condensed combined financial statements reflect certain
assumptions deemed probable by management regarding the proposed merger (e.g.,
that share information used in the pro forma information approximates actual
share information at the Effective Date). No adjustments to the pro forma
condensed combined financial information have been made to account for different
possible results in connection with the foregoing, as management believes that
the impact on such information of the varying outcomes, individually or in the
aggregate, would not be materially different.

The unaudited pro forma condensed combined balance sheet as of March 31, 2000
combines the historical consolidated balance sheet of Celgene and the historical
balance sheet of Signal, giving effect to the merger as if it had been
consummated on March 31, 2000. The unaudited pro forma condensed combined
statements of operations combine the historical consolidated statements of
operations of Celgene and the historical statements of operations of Signal as
if the companies have been combined for all periods presented.

Celgene and Signal estimate that they will incur direct transaction costs of
approximately $7.5 million associated with the merger, which will be charged to
operations upon consummation of the merger.

Such pro forma condensed combined financial information is presented for
illustrative purposes only and is not necessarily indicative of the financial
position and results of operations that would have been actually achieved had
the merger occurred at the beginning of the periods presented, nor is it
necessarily indicative of future financial position or results of operations.
These pro forma condensed combined financial statements are based upon, and
should be read in conjunction with the respective historical consolidated
financial statements of Celgene, which are incorporated herein by reference, and
the historical financial statements of Signal, which are included elsewhere in
this proxy statement/prospectus.


                                       11
<PAGE>

             UNAUDITED PRO FORMA CONDENSED COMBINED BALANCE SHEET
                             AS OF MARCH 31, 2000
                (IN THOUSANDS, EXCEPT SHARE AND PER SHARE DATA)

<TABLE>
<CAPTION>
                                                                                          PRO FORMA     PRO FORMA
                                                                CELGENE       SIGNAL     ADJUSTMENTS    COMBINED
                                                             ------------- ------------ ------------- ------------
                                                                                         (SEE NOTE 3)
<S>                                                          <C>           <C>          <C>           <C>
ASSETS
Current assets:
  Cash and cash equivalents ................................  $  162,907    $   5,815     $            $  168,722
  Marketable securities available for sale .................     129,458          522                     129,980
  Accounts receivable ......................................       5,689           78                       5,767
  Inventory ................................................       2,615           --                       2,615
  Other current assets .....................................       1,701        1,050                       2,751
                                                              ----------    ---------     ---------    ----------
   Total current assets ....................................     302,370        7,465                     309,835
  Plant and equipment, net .................................       2,436        3,101                       5,537
  Other assets .............................................       2,359        1,084                       3,443
                                                              ----------    ---------     ---------    ----------
   Total assets ............................................  $  307,165    $  11,650     $            $  318,815
                                                              ==========    =========     =========    ==========
LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
  Accounts payable .........................................  $    2,573    $     738     $            $    3,311
  Accrued expenses .........................................       4,072        1,388                       5,460
  Accrued merger costs .....................................          --           --         7,500         7,500
  Current portion of capital lease and note obligation .....         145          921                       1,066
  Current portion of deferred revenue ......................          --        3,525                       3,525
                                                              ----------    ---------                  ----------
   Total current liabilities ...............................       6,790        6,572         7,500        20,862
  Capitalized lease and note obligation-net of current
   portion .................................................           9        1,570                       1,579
  Other non-current liabilities ............................          --           97                          97
  Long-term convertible notes ..............................      29,243           --                      29,243
                                                              ----------    ---------                  ----------
   Total liabilities .......................................      36,042        8,239         7,500        51,781
                                                              ----------    ---------         -----    ----------
Stockholders' equity:
  Preferred stock, $.01 par value per share, 5,000,000
   authorized; none outstanding at March 31, 2000 ..........          --           --            --            --
  Convertible preferred stock, 24,742,639 authorized;
   24,492,639 shares issued and outstanding at March
   31, 2000 ................................................          --       41,331       (41,331)           --
  Common stock, $.01 par value per share, 120,000,000
   authorized; issued and outstanding 64,318,539 shares
   at March 31, 2000 (issued and outstanding 67,971,697
   shares pro forma combined) (see note 3) .................         643           --            37           680
  Common stock, 35,288,708 authorized; issued and
   outstanding 4,569,873 shares at March 31, 2000 ..........          --       11,313       (11,313)           --
  Additional paid-in capital (see note 3) ..................     440,389           --        52,607       492,996
  Deferred compensation ....................................          --       (7,843)           --        (7,843)
  Notes receivable from stockholders .......................          --         (133)           --          (133)
  Accumulated deficit ......................................    (169,538)     (41,257)       (7,500)     (218,295)
  Accumulated other comprehensive loss .....................        (371)          --            --          (371)
                                                              ----------    ---------       -------    ----------
   Total stockholders' equity ..............................     271,123        3,411        (7,500)      267,034
                                                              ----------    ---------       -------    ----------
   Total liabilities and stockholders' equity ..............  $  307,165    $  11,650     $      --    $  318,815
                                                              ==========    =========     =========    ==========

</TABLE>

-----------
See accompanying notes to unaudited pro forma condensed combined financial
statements.

                                       12
<PAGE>

                     UNAUDITED PRO FORMA CONDENSED COMBINED
                            STATEMENT OF OPERATIONS
                   FOR THE THREE MONTHS ENDED MARCH 31, 2000

<TABLE>
<CAPTION>
                                                                                                 PRO FORMA
                                                                          CELGENE      SIGNAL    COMBINED
                                                                      ------------- ----------- -----------
                                                                      (IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                                                                     <C>         <C>         <C>
Revenues:
  Product sales .......................................................  $ 11,666    $     --    $ 11,666
  Research contracts ..................................................       200       2,671       2,871
                                                                         --------    --------    --------
   Total revenues .....................................................    11,866       2,671      14,537
Expenses:
  Cost of goods sold ..................................................     1,664          --       1,664
  Research and development ............................................     6,386       5,167      11,553
  Selling, general and administrative .................................     8,496       1,037       9,533
                                                                         --------    --------    --------
   Total expenses .....................................................    16,546       6,204      22,750
Operating loss ........................................................    (4,680)     (3,533)     (8,213)
Other income and expense:
  Interest income .....................................................     2,314         116       2,430
  Interest expense ....................................................       778          63         841
                                                                         --------    --------    --------
Loss from continuing operations .......................................    (3,144)     (3,480)     (6,624)
                                                                         ========    ========    ========
Per share basic and diluted:
  Loss from continuing operations .....................................  $  (0.05)   $  (0.98)   $  (0.11)
                                                                         ========    ========    ========
Weighted average number of shares of common stock outstanding .........    58,706       3,538      59,151
                                                                         ========    ========    ========
Pro forma basic and diluted per share data assuming conversion of
  Signal preferred stock to common stock:
  Loss from continuing operations .....................................                          $  (0.11)
                                                                                                 ========
  Weighted average number of shares of common stock
   outstanding ........................................................                            62,299
                                                                                                 ========
</TABLE>

See accompanying notes to unaudited pro forma condensed combined financial
statements.

                                       13
<PAGE>

                     UNAUDITED PRO FORMA CONDENSED COMBINED
                             STATEMENT OF OPERATIONS
                      FOR THE YEAR ENDED DECEMBER 31, 1999
<TABLE>
<CAPTION>
                                                                                              PRO FORMA
                                                                     CELGENE      SIGNAL      COMBINED
                                                                  ------------ ----------- --------------
                                                                   (IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                                                               <C>          <C>         <C>
Revenues:
  Product sales .................................................  $  24,052    $     --     $   24,052
  Research contracts ............................................      2,158      11,748         13,906
                                                                   ---------    --------     ----------
   Total revenues ...............................................     26,210      11,748         37,958
Expenses:
  Cost of goods sold ............................................      2,983          --          2,983
  Research and development ......................................     19,646      16,747         36,393
  Selling, general and administrative ...........................     26,236       3,011         29,247
                                                                   ---------    --------     ----------
   Total expenses ...............................................     48,865      19,758         68,623
Operating loss ..................................................    (22,655)     (8,010)       (30,665)
Other income and expense:
  Interest income ...............................................        694         607          1,301
  Interest expense ..............................................      2,838         453          3,291
                                                                   ---------    --------     ----------
Loss before tax benefit .........................................    (24,799)     (7,856)       (32,655)
Tax benefit .....................................................      3,018          --          3,018
                                                                   ---------    --------     ----------
Loss from continuing operations .................................    (21,781)     (7,856)       (29,637)
  Preferred stock dividend (including accretion and imputed
   dividends) ...................................................         --         818            818
                                                                   ---------    --------     ----------
Loss from continuing operations applicable to common
  stockholders ..................................................  $ (21,781)   $ (8,674)    $  (30,455)
                                                                   =========    ========     ==========
Per share basic and diluted:
  Loss from continuing operations applicable to common
   stockholders .................................................  $   (0.43)   $  (2.64)    $    (0.59)
                                                                   =========    ========     ==========
Weighted average number of shares of common stock outstanding....     51,036       3,282         51,449
                                                                   =========    ========     ==========
Pro forma  basic  and  diluted  per share  data  assuming  conversion  of Signal
  preferred stock to common stock: Loss from continuing operations applicable to
  common
   stockholders .................................................                            $    (0.56)
                                                                                             ==========
  Weighted average number of shares of common stock
   outstanding ..................................................                                54,494
                                                                                             ==========

</TABLE>

See accompanying notes to unaudited pro forma condensed combined financial
statements.

                                       14
<PAGE>

                     UNAUDITED PRO FORMA CONDENSED COMBINED
                             STATEMENT OF OPERATIONS
                      FOR THE YEAR ENDED DECEMBER 31, 1998

<TABLE>
<CAPTION>
                                                                                       PRO FORMA
                                                               CELGENE      SIGNAL     COMBINED
                                                            ------------ ----------- ------------
                                                            (IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                                                         <C>          <C>         <C>
Revenues:
  Product sales ...........................................  $   3,266    $     --    $   3,266
  Research contracts ......................................        535      15,414       15,949
                                                             ---------    --------    ---------
   Total revenues .........................................      3,801      15,414       19,215
Expenses:
  Cost of goods sold ......................................        282          --          282
  Research and development ................................     19,772      15,573       35,345
  Selling, general and administrative .....................     16,219       4,798       21,017
                                                             ---------    --------    ---------
   Total expenses .........................................     36,273      20,371       56,644
Operating loss ............................................    (32,472)     (4,957)     (37,429)
Other income and expense:
  Interest income .........................................        705       1,053        1,758
  Interest expense ........................................        256         452          708
                                                             ---------    --------    ---------
Loss from continuing operations ...........................    (32,023)     (4,356)     (36,379)
  Preferred stock dividend (including accretion and imputed
   dividends) .............................................         25          --           25
                                                             ---------    --------    ---------
Loss from continuing operations applicable to common
  stockholders ............................................  $ (32,048)   $ (4,356)   $ (36,404)
                                                             =========    ========    =========
Per share basic and diluted:
  Loss from continuing operations applicable to common
   stockholders ...........................................  $   (0.66)   $  (1.65)   $   (0.75)
Weighted average number of shares of common stock
  outstanding .............................................     48,480       2,636       48,811
                                                             =========    ========    =========
</TABLE>

See accompanying notes to unaudited pro forma condensed combined financial
statements.

                                       15
<PAGE>

                     UNAUDITED PRO FORMA CONDENSED COMBINED
                             STATEMENT OF OPERATIONS
                     FOR THE YEAR ENDED DECEMBER 31, 1997

<TABLE>
<CAPTION>
                                                                                       PRO FORMA
                                                               CELGENE      SIGNAL     COMBINED
                                                            ------------ ----------- ------------
                                                            (IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                                                         <C>          <C>         <C>
Revenues:
  Product sales ...........................................  $      --    $     --    $      --
  Research contracts ......................................      1,122       7,579        8,701
                                                             ---------    --------    ---------
   Total revenues .........................................      1,122       7,579        8,701
Expenses:
  Cost of goods sold ......................................         --          --           --
  Research and development ................................     17,380      10,337       27,717
  Selling, general and administrative .....................      9,146       2,791       11,937
                                                             ---------    --------    ---------
   Total expenses .........................................     26,526      13,128       39,654
Operating loss ............................................    (25,404)     (5,549)     (30,953)
Other income and expense:
  Interest income .........................................        496         326          822
  Interest expense ........................................        112         517          629
                                                             ---------    --------    ---------
Loss from continuing operations ...........................    (25,020)     (5,740)     (30,760)
  Preferred stock dividend (including accretion and imputed
   dividends) .............................................      1,474          --        1,474
                                                             ---------    --------    ---------
Loss from continuing operations applicable to common
  stockholders ............................................  $ (26,494)   $ (5,740)   $ (32,234)
                                                             =========    ========    =========
Per share basic and diluted:
  Loss from continuing operations applicable to common
   stockholders ...........................................  $   (0.72)   $  (2.82)   $   (0.87)
                                                             =========    ========    =========
Weighted average number of shares of common stock
  outstanding .............................................     36,645       2,032       36,900
                                                             =========    ========    =========
</TABLE>

See accompanying notes to unaudited pro forma condensed combined financial
statements.

                                       16
<PAGE>

                          NOTES TO UNAUDITED PRO FORMA
                     CONDENSED COMBINED FINANCIAL STATEMENTS


1. DESCRIPTION OF TRANSACTION AND BASIS OF PRESENTATION


     The merger agreement provides that each outstanding share of Signal common
stock (including shares of Signal preferred stock which will be converted into
Signal common stock on a one-for-one basis immediately before the merger), other
than shares owned by holders who are exercising dissenters' rights under
California law, will be converted into the right to receive 0.1257 of a share of
Celgene common stock, par value $.01 per share in a tax-free transaction. Also,
the merger agreement provides that each option and warrant to purchase Signal
common stock or preferred stock will be converted into an option or warrant to
acquire Celgene common stock based on the aforementioned exchange ratio. Based
on Signal options and warrants outstanding as of July 20, 2000, Celgene would
issue a total of approximately 431,000 options and warrants. The merger is
expected to be completed later this year. It is intended to be accounted for
under the pooling-of-interests method and, accordingly, financial statements of
the combined company will include Celgene's historical consolidated financial
statements restated to include the historical financial statements of Signal.
The merger is subject to customary closing conditions, including regulatory
approval.


2. ACCOUNTING POLICIES AND FINANCIAL STATEMENT CLASSIFICATIONS


Upon consummation of the merger, Celgene and Signal will review their accounting
policies and financial statement classifications. As a result of that review, it
may become necessary to restate the combined entity's financial statements to
conform to those accounting policies and classifications that are determined to
be more appropriate.


3. PRO FORMA ADJUSTMENTS


Adjustments to preferred stock, common stock, and additional paid-in-capital in
the unaudited pro forma condensed combined balance sheet at March 31, 2000
reflect the conversion of Signal's preferred shares to common shares just prior
to the merger and the issuance of Celgene's common stock in exchange for
Signal's common shares at the exchange ratio described in footnote 1. These
amounts were determined by multiplying Signal's outstanding preferred and common
shares at March 31, 2000 by the exchange ratio of 0.1257. The number of shares
to be issued at completion of the merger will be based on the actual number of
common and preferred shares of Signal outstanding at that time. In addition,
Celgene's historical common shares issued and outstanding at March 31, 2000 was
adjusted in the unaudited pro forma condensed combined balance sheet to reflect
Celgene's three-for-one stock split declared and issued on April 14, 2000.


Celgene and Signal estimate that they will incur direct transaction costs of
approximately $7.5 million associated with the merger consisting of transaction
fees for financial advisors, attorneys, accountants, financial printing and
other related charges. These nonrecurring transaction costs will be charged to
operations upon consummation of the merger. The unaudited pro forma condensed
combined balance sheet gives effect to the estimated direct transaction costs by
an increase to accumulated deficit and accrued merger costs. The estimated
direct transaction costs are not reflected in the unaudited pro forma condensed
combined statements of operations.


The pro forma combined basic and diluted earnings per share for the respective
periods presented are based on the combined basic and diluted weighted average
common shares of Celgene and Signal for each respective period. The historical
basic and diluted weighted average shares for Signal were converted at the
exchange ratio of 0.1257 of a share of Celgene common stock for each Signal
common stock outstanding.


                                       17
<PAGE>

                         NOTES TO UNAUDITED PRO FORMA
             CONDENSED COMBINED FINANCIAL STATEMENTS - (CONTINUED)

3. PRO FORMA ADJUSTMENTS - (CONTINUED)

The following table reconciles the numbers of shares used in the pro forma
combined per share computations to the numbers set forth in Celgene's and
Signal's historical statements of operations:

<TABLE>
<CAPTION>
                                                    THREE MONTHS
                                                       ENDED                YEARS ENDED DECEMBER 31,
                                                     MARCH 31,     ------------------------------------------
                                                        2000           1999          1998          1997
                                                   -------------   -----------   -----------   -----------
<S>                                                <C>             <C>           <C>           <C>
Shares used in per share calculation
 (in thousands, except estimated exchange ratio)
Historical -- Celgene ..........................       58,706         51,036        48,480        36,645
Historical -- Signal ...........................        3,538          3,282         2,636         2,032
Estimated exchange ratio .......................        0.1257         0.1257        0.1257        0.1257
                                                       -------        -------       -------       -------
                                                          445            413           331           255
Pro forma combined .............................       59,151         51,449        48,811        36,900
                                                       =======        =======       =======       =======
</TABLE>

Conversion of the Signal convertible preferred stock outstanding was not assumed
for purposes of calculating the pro forma combined per share amounts because the
effect would be anti-dilutive.

     The pro forma  basic and  diluted  per share data  assuming  conversion  of
Signal preferred stock to common stock for the three months ended March 31, 2000
and December 31, 1999 gives effect to the assumed  conversion of such  preferred
stock into  common  stock as of January 1, 1999 or the date of  issuance of such
preferred stock, if later.


4. FORWARD-LOOKING STATEMENTS

The statements contained in this section may be deemed to be forward-looking
statements within the meaning of Section 27A of the Securities Act.
Forward-looking statements are typically identified by the words "believe,"
"expect," "anticipate," "intend," "estimate," and similar expressions. These
forward-looking statements are based largely on management's expectations and
are subject to a number of uncertainties. Actual results could differ materially
from these forward-looking statements. Neither Celgene nor Signal undertake any
obligation to update publicly or revise any forward-looking statements. For a
more complete discussion of the risks and uncertainties which may affect such
forward-looking statements, please refer to the section entitled
"Forward-Looking Statements."


                                       18
<PAGE>

                                  RISK FACTORS

In addition to the other information contained or incorporated by reference in
this proxy statement/prospectus, Signal shareholders should consider the
following risk factors before they decide whether or not to vote in favor of the
approval and adoption of the merger agreement, approval of the principal terms
of the merger and conversion of the outstanding shares of preferred stock into
shares of common stock. All share amounts of Celgene have been adjusted to
reflect the three-for-one stock split declared by Celgene and issued on April
14, 2000.


                          RISKS RELATING TO THE MERGER


FAILURE TO REALIZE THE BENEFITS OF INTEGRATING CELGENE'S AND SIGNAL'S
BUSINESSES, OPERATIONS AND PERSONNEL COULD DIMINISH THE EXPECTED BENEFITS OF THE
MERGER.

Achieving the expected benefits of the merger will depend in large part on the
successful integration of Celgene's and Signal's businesses, operations and
personnel in a timely and efficient manner. Celgene will need to integrate the
information systems, product development, administration and other organizations
of the two companies and the geographical distance between Celgene's facilities
in Warren, New Jersey, and Signal's facilities in San Diego, California. This
will be difficult and unpredictable because of possible cultural conflicts and
different opinions on technical, operational and other integration decisions.
Celgene will also need to integrate the employees of the two companies. Celgene
or Signal may experience disruption in its employee base as a result of
uncertainty in connection with the merger. There is also a risk that key
employees of Signal may seek employment elsewhere, including with competitors.
The operations, management and personnel of the two companies may not be
compatible, and Celgene or Signal may also experience the loss of key personnel
for that reason.

The diversion of management attention and any difficulties or delays encountered
in the transition and integration process could have a material adverse effect
on the combined company's business, financial condition and operating results.

Celgene expects to incur costs from integrating Signal's operations and
personnel. These costs may be substantial and may include costs for:

o employee redeployment or severance; and

o conversion of information systems.

Celgene and Signal cannot assure you that they will be successful in these
integration efforts or that Celgene will realize the expected benefits of the
merger.

SIGNAL SHAREHOLDERS WILL RECEIVE A FIXED NUMBER OF SHARES OF CELGENE COMMON
STOCK IN THE MERGER, NOT A FIXED VALUE.

Upon completion of the merger, each of your shares will be converted into 0.1257
of a share of Celgene common stock. Since the exchange ratio is fixed, the
number of shares that Signal shareholders will receive in the merger will not
change, even if the market price of Celgene common stock changes. There will be
no adjustment of the exchange ratio or termination of the merger based solely on
fluctuations in the price of Celgene common stock. The market price of Celgene
common stock is subject to fluctuation. These market fluctuations may cause a
decline in the market price of Celgene common stock. The market price of Celgene
common stock upon and after completion of the merger could be lower than the
market price on the date of the merger agreement or the current market price.
Signal shareholders should obtain recent market quotations of Celgene common
stock before they vote on the merger.

IF THE MERGER AGREEMENT IS TERMINATED UNDER SPECIFIED CIRCUMSTANCES, SIGNAL MAY
HAVE TO PAY A SUBSTANTIAL BREAK-UP FEE OR LIQUIDATED DAMAGES TO CELGENE.

The merger agreement provides that if Signal's board withdraws its
recommendation that shareholders vote for the merger or solicits or recommends
another acquisition transaction with a third party, Signal will be required to
pay Celgene a termination fee of $10,000,000. If the merger is not completed by
December 31, 2000 and Celgene terminates the merger agreement, or if Signal
shareholders do not approve the merger, then Signal will also be required to pay
Celgene a termination fee of $10,000,000 if Signal signs or


                                       19
<PAGE>

completes another acquisition transaction with a third party within one year. In
addition,  if Signal or Celgene  terminates the merger agreement  because of any
material breach by the other of any  representation,  warranty or covenant under
the merger  agreement,  the  breaching  party will be  required to pay the other
party $5,000,000.


                            RISKS RELATING TO CELGENE

In addition to other information in this proxy statement/prospectus, you should
carefully consider the following risk factors in evaluating Celgene's business.


RISKS ASSOCIATED WITH INVESTING IN CELGENE COMMON STOCK


THE PRICE OF CELGENE COMMON STOCK HAS EXPERIENCED SUBSTANTIAL VOLATILITY AND MAY
CONTINUE TO DO SO IN THE FUTURE.

There has been significant volatility in the market prices for publicly traded
shares of pharmaceutical companies, including Celgene. In 1999, the price of
Celgene's common stock fluctuated from a low of $3.833 to a high of $24.208. On
July 20, 2000, Celgene's common stock closed at a price of $49.125. The price of
Celgene's common stock may not remain at or exceed current levels. The following
factors may cause the market price of Celgene's common stock to decline:

o announcements of technical or product developments by Celgene or its
  competitors;

o market conditions for pharmaceutical and biotechnology stocks;

o market conditions generally;

o governmental regulation;

o healthcare legislation;

o public  announcements  regarding  medical  advances  in  the  treatment of the
  disease states that Celgene is targeting;

o patent or proprietary rights developments;

o changes in third-party reimbursement policies for Celgene's products;

o fluctuations in Celgene's operating results;

o unsuccessful clinical trials; or

o public announcement of the merger.


THE NUMBER OF SHARES OF CELGENE COMMON STOCK ELIGIBLE FOR FUTURE SALE COULD
CAUSE THE MARKET PRICE OF ITS COMMON STOCK TO DECLINE.

Future sales of substantial amounts of Celgene's common stock could cause the
market price of its common stock to decline. As of December 31, 1999, there were
outstanding stock options for 6,981,801 shares of common stock, of which
2,901,702 were currently exercisable, and warrants either outstanding or
issuable upon demand that are exercisable for 1,653,132 shares of common stock.
In addition, as part of the merger, Celgene will be assuming 3,123,394
outstanding options and 475,000 outstanding warrants of Signal of which
3,123,394 outstanding options and 400,000 outstanding warrants will be
exercisable for shares of Celgene common stock. Moreover, as of July 20, 2000,
the 9.25% convertible note issued on September 16, 1998 can be converted into
2,386,389 shares of common stock, the 9.0% convertible notes issued on January
20, 1999 can be converted into 285,801 shares of common stock and the 9.0%
convertible notes issued on July 6, 1999 can be converted into 1,578,876 shares
of common stock.


                                       20
<PAGE>

CELGENE MAY ISSUE ADDITIONAL EQUITY SECURITIES, WHICH WOULD LEAD TO DILUTION OF
YOUR OWNERSHIP INTEREST.

Celgene may seek to raise capital from an offering of senior and subordinated
debt securities, common stock, preferred stock or a combination thereof, at such
times and in such amounts as Celgene deems appropriate. These securities may be
used to acquire technology, products, product rights and businesses, among other
purposes. The issuance of additional equity securities or securities convertible
into equity securities for these or other purposes would result in dilution of
existing stockholders' equity interests in Celgene.


CELGENE'S SHAREHOLDER RIGHTS PLAN AND CERTAIN CHARTER AND BY-LAW PROVISIONS MAY
DETER A THIRD PARTY FROM ACQUIRING IT.

Celgene's board of directors has adopted a shareholder rights plan, the purpose
of which is to protect stockholders against unsolicited attempts to acquire
control of Celgene that do not offer a fair price to all of its stockholders.
The rights plan may have the effect of dissuading a potential acquiror from
making an offer for Celgene's common stock at a price that represents a premium
to the then current trading price.

Celgene's board of directors has the authority to issue, at any time, without
further stockholder approval, up to 5,000,000 shares of preferred stock, and to
determine the price, rights, privileges and preferences of those shares. Any
issuance of preferred stock could discourage a third party from acquiring a
majority of Celgene's outstanding voting stock. Additionally, Celgene's board of
directors has adopted certain amendments to its by-laws intended to strengthen
its board's position in the event of a hostile takeover attempt.

Furthermore, Celgene is subject to the provisions of Section 203 of the Delaware
General Corporation Law, an anti-takeover law, which may also dissuade a
potential acquiror of its common stock.


RISKS ASSOCIATED WITH INVESTING IN THE BUSINESS OF CELGENE.

IF CELGENE IS UNSUCCESSFUL IN DEVELOPING AND COMMERCIALIZING ITS PRODUCTS, ITS
BUSINESS, FINANCIAL CONDITION AND RESULTS OF OPERATIONS COULD BE MATERIALLY
ADVERSELY AFFECTED.

Many of Celgene's products and processes are in the early or mid-stages of
development and will require the commitment of substantial resources, extensive
research, development, preclinical testing, clinical trials, manufacturing
scale-up and regulatory approval prior to being ready for sale. Celgene has not
yet sold any of its products other than THALOMID(Reg. TM). All of its other
products will require further development, clinical testing and regulatory
approvals, and Celgene cannot assure you that commercially viable products will
result from these efforts. If any of Celgene's products, even if developed and
approved, cannot be successfully commercialized, Celgene's business, financial
condition and results of operations could be materially adversely affected.


DURING THE NEXT SEVERAL YEARS, CELGENE WILL BE VERY DEPENDENT ON THE COMMERCIAL
SUCCESS OF THALOMID.

At Celgene's present level of operations, it may not be able to attain
profitability if physicians prescribe THALOMID only for those who are diagnosed
with erythema nodosum leprosum, or ENL. Under current regulations of the U.S.
Food and Drug Administration, or FDA, Celgene is precluded from promoting
THALOMID outside this approved use. The market for the use of THALOMID in
patients suffering from ENL is relatively small. Celgene has initiated clinical
studies to examine whether or not THALOMID is effective and safe when used to
treat disorders other than ENL, but Celgene does not know whether these studies
will in fact demonstrate safety and efficacy, or if they do, whether Celgene
will succeed in receiving regulatory clearance to market THALOMID for additional
indications. If the results of these studies are negative, or if adverse
experiences are reported in these clinical studies or otherwise in connection
with the use of THALOMID by patients, this could undermine physician and patient
comfort with the product, could limit the commercial success of the product and
could even impact the acceptance of THALOMID in the ENL market. FDA regulations
restrict Celgene's ability to communicate the results of additional clinical
studies to patients and physicians without first obtaining approval from the FDA
to expand the authorized uses for this product.


                                       21
<PAGE>

IF CELGENE'S PRODUCTS ARE NOT ACCEPTED BY THE MARKET, ITS BUSINESS, FINANCIAL
CONDITION AND RESULTS OF OPERATIONS COULD BE MATERIALLY ADVERSELY AFFECTED.

Celgene cannot assure you that those of Celgene's products that receive
regulatory clearance, including THALOMID, or those products for which no
regulatory clearance, is required, will achieve market acceptance. A number of
factors render the degree of market acceptance of its products uncertain,
including the extent to which Celgene can demonstrate the products' efficacy,
safety and advantages, if any, over competing products, as well as the
reimbursement policies of third party payors, such as government and private
insurance plans. Failure of Celgene's products to achieve market acceptance
would have a material adverse effect on its business, financial condition and
results of operations.


CELGENE FACES A RISK OF PRODUCT LIABILITY CLAIMS AND MAY NOT BE ABLE TO OBTAIN
INSURANCE.

Celgene may be subject to product liability or other claims based on allegations
that the use of its technology or products has resulted in adverse effects,
whether by participants in its clinical trials or by patients using its
products. Thalidomide, when used by pregnant women, has resulted in serious
birth defects. Therefore, necessary and strict precautions must be taken by
physicians prescribing the drug to women with childbearing potential, and
Celgene cannot assure you that such precautions will be observed in all cases
or, if observed, will be effective. Use of thalidomide has also been associated,
in a limited number of cases, with other side effects, including nerve damage.
Although Celgene has product liability insurance that it believes is
appropriate, Celgene cannot assure you that it will be able to obtain additional
coverage if required, or that such coverage will be adequate to protect Celgene
in the event claims are asserted against it. Celgene's obligation to defend
against or pay any product liability or other claim may have a material adverse
effect on its business, financial condition and results of operations.


CELGENE HAS A HISTORY OF OPERATING LOSSES AND AN ACCUMULATED DEFICIT AND MAY
NEED TO SEEK ADDITIONAL FUNDING.

Celgene has sustained losses in each year since its incorporation in 1986.
Celgene sustained net losses of $21.8 million and $25.1 million for the years
ended December 31, 1999 and 1998, respectively, and $3.1 million for the three
months ended March 31, 2000. Celgene had an accumulated deficit of $166.4
million and $144.6 million at December 31, 1999 and 1998, respectively, and
$169.5 million at March 31, 2000. Celgene expects to make substantial
expenditures to further develop and commercialize its products, and, based on
these expenditures, it is probable that losses will continue for at least the
next six months or longer depending on when the merger is completed. Celgene
expects that its rate of spending will accelerate as the result of increased
clinical trial costs and expenses associated with regulatory approval and
commercialization of products now in development. In order to fund its future
operations, Celgene may seek additional capital. Celgene may not be able to
raise additional capital on reasonable terms, or at all. Celgene cannot assure
you, assuming it successfully raises additional funds, that Celgene will achieve
profitability or positive cash flow.


CELGENE MAY EXPERIENCE SIGNIFICANT FLUCTUATIONS IN ITS QUARTERLY OPERATING
RESULTS.

Celgene has historically experienced, and expects to continue for the
foreseeable future to experience, significant fluctuations in its quarterly
operating results. These fluctuations are due to a number of factors, many of
which are outside its control, and may result in volatility of its stock price.
Future operating results will depend on many factors, including:

o demand for its products;

o regulatory approvals for its products;

o the  timing  of  the  introduction  and  market  acceptance of new products by
  Celgene or competing companies;

o the timing of certain research and development milestones; and

o Celgene's ability to control its costs.

                                       22
<PAGE>

CELGENE HAS NO MANUFACTURING CAPABILITIES AND IS DEPENDENT ON ONE SUPPLIER FOR
THE RAW MATERIAL AND ONE MANUFACTURER FOR THE FORMULATION AND ENCAPSULATION OF
THALOMID.

Celgene currently has no experience in, or its own facilities for, manufacturing
any products on a commercial scale. Currently, Celgene obtains all of its bulk
drug material for THALOMID from a single supplier and relies on a single
manufacturer to formulate and encapsulate THALOMID. The FDA requires that all
suppliers of pharmaceutical bulk material and all manufacturers of
pharmaceuticals for sale in or from the United States achieve and maintain
compliance with the FDA's current Good Manufacturing Practice, or cGMP,
regulations and guidelines. If the operations of the sole supplier or the sole
manufacturer were to become unavailable for any reason, the required FDA review
and approval of the operations of a new supplier or new manufacturer could cause
a delay in the manufacture of THALOMID which could have a material adverse
effect on Celgene's business, financial condition and results of operations.
Celgene intends to continue to utilize outside manufacturers if and when needed
to produce its other products on a commercial scale. If outside manufacturers do
not meet its requirements for quality, quantity or timeliness, or do not achieve
and maintain compliance with all applicable regulations, Celgene's business,
financial condition and results of operations could be materially adversely
affected.


CELGENE HAS LIMITED MARKETING AND DISTRIBUTION CAPABILITIES.

Although Celgene has an 80-person sales and commercialization group to sell
THALOMID, it may be required to seek a corporate partner to provide marketing
services with respect to its other products. Any delay in developing these
resources could have a material adverse impact on its results of operations.
Celgene has contracted with a specialty distributor to distribute THALOMID.
Failure of this specialty distributor to perform its obligations could have a
material adverse effect on Celgene's business, financial condition and results
of operations.


CELGENE IS DEPENDENT ON COLLABORATIONS AND LICENSES WITH THIRD PARTIES.

Celgene's ability to fully commercialize its products, if developed, may depend
to some extent upon joint ventures or other arrangements with established
pharmaceutical companies with the requisite experience and financial and other
resources to obtain regulatory approvals and to manufacture and market such
products. Accordingly, Celgene's success may depend, in part, upon the
subsequent success of such third parties in performing preclinical and clinical
trials, obtaining the requisite regulatory approvals, scaling up manufacturing,
successfully commercializing the licensed product candidates and otherwise
performing their obligations to Celgene. Celgene cannot assure you that:

o  Celgene will be able to enter into joint ventures or other arrangements on
   acceptable terms, if at all;

o  Celgene's joint ventures or other arrangements will be successful;

o  Celgene's joint ventures or other arrangements will lead to the successful
   development and commercialization of any products;

o  Celgene will be able to obtain or maintain proprietary rights or licenses to
   any technology or products developed in connection with its joint ventures or
   other arrangements; or

o  Celgene will be able to preserve the confidentiality of any proprietary
   rights or information developed in connection with its joint ventures or
   other arrangements.


THE HAZARDOUS MATERIALS CELGENE USES IN ITS RESEARCH AND DEVELOPMENT COULD
RESULT IN SIGNIFICANT LIABILITIES WHICH COULD EXCEED ITS INSURANCE COVERAGE AND
FINANCIAL RESOURCES.

Celgene uses some hazardous materials in its research and development
activities. While Celgene believes that it is currently in substantial
compliance with the federal, state and local laws and regulations governing the
use of these materials, it cannot assure you that accidental injury or
contamination will not occur. Any such accident or contamination could result in
substantial liabilities, which could exceed Celgene's insurance coverage and
financial resources. Additionally, Celgene cannot assure you that the cost of
compliance with environmental and safety laws and regulations will not increase
in the future.


                                       23
<PAGE>

          RISKS RELATING TO INVESTING IN THE PHARMACEUTICAL INDUSTRY


THE PHARMACEUTICAL AND AGROCHEMICAL INDUSTRIES ARE SUBJECT TO EXTENSIVE
GOVERNMENT REGULATION AND THERE IS NO ASSURANCE OF REGULATORY APPROVAL.

The preclinical development, clinical trials, manufacturing, marketing and
labeling of pharmaceuticals are all subject to extensive regulation by numerous
governmental authorities and agencies in the United States and other countries.
Celgene cannot assure you that the combined company will be able to obtain the
necessary approvals required to market its products in any of these markets. The
testing, marketing and manufacturing of its products will require marketing
clearance from one or more of the following named governmental agencies, the FDA
and, in some cases, from the U.S. Environmental Protection Agency, or the EPA,
and the U.S. Department of Agriculture, or the USDA, as well as governmental
authorities outside of the United States which perform similar roles. Certain of
the combined company's pharmaceutical products in development also fall under
the Controlled Substances Act of 1970, or the CSA, which requires authorization
by the U.S. Drug Enforcement Administration, or the DEA, of the U.S. Department
of Justice in order to handle and distribute these products. It is not possible
to predict how long the approval processes of the FDA, EPA, DEA or any other
applicable federal, state or foreign regulatory authority or agency for any of
the combined company's products will take or whether any such approvals
ultimately will be granted. Positive results in preclinical testing and/or early
phases of clinical studies are no assurance of success in later phases of the
approval process. Risks associated with the regulatory approval process include:

o  in general, preclinical tests and clinical trials can take many years, and
   require the expenditure of substantial resources, and the data obtained from
   these tests and trials can be susceptible to varying interpretation that
   could delay, limit or prevent regulatory clearance;

o  delays or rejections may be encountered during any stage of the regulatory
   approval process based upon the failure of the clinical or other data to
   demonstrate compliance with, or upon the failure of the product to meet, a
   regulatory agency's requirements for safety, efficacy and quality or, in the
   case of a product seeking an orphan drug indication, because another designee
   received clearance first;

o  requirements for clearance may become more stringent due to changes in
   regulatory agency policy, or the adoption of new regulations or legislation;

o  the scope of any regulatory clearance, when obtained, may significantly limit
   the indicated uses for which a product may be marketed;

o  drugs and agrochemicals, as well as their manufacturers, are subject to
   continuing and on-going review after marketing clearance, and discovery of
   previously unknown problems with these products may result in restrictions on
   their manufacture, sale or use or in their withdrawal from the market; and

o  regulatory authorities and agencies may promulgate additional regulations
   restricting the sale of existing and proposed products.

Once a product receives marketing clearance, Celgene cannot guarantee that the
FDA will permit the combined company to market that product for broader or
different applications, or that it will grant the combined company clearance
with respect to separate product applications which represent extensions of the
basic technology, or that existing clearances will not be withdrawn or modified
in a significant manner. In addition, it is possible that the FDA will
promulgate additional regulations restricting the sale of the combined company's
present or proposed products.

Labeling and promotional activities are subject to scrutiny by the FDA and state
regulatory agencies and, in some circumstances, by the Federal Trade Commission.
FDA enforcement policy prohibits the marketing of approved products for
unapproved, or off-label, uses. These regulations, and the FDA's interpretation
of them, may impair the combined company's ability to effectively market
THALOMID or other products which gain marketing clearance. The FDA actively
enforces regulations and policies prohibiting promotion of off-label uses and
the promotion of products for


                                       24
<PAGE>

which marketing clearance has not been obtained. Failure to comply with these
requirements can result in regulatory enforcement action by the FDA. The FDA is
aware that physicians prescribe THALOMID for off-label uses and on April 21,
2000 Celgene received an FDA Warning Letter regarding off-label promotion.
Celgene has responded to the FDA and believes it has taken all actions necessary
to insure that THALOMID is properly and safely commercialized. FDA clearance of
THALOMID requires that Celgene distribute it under the rigid standards of its
S.T.E.P.S. program in order to maintain such clearances.

Delays in obtaining, or the failure to obtain and maintain, necessary approvals
from the FDA, EPA, DEA or other applicable regulatory authorities or agencies
for the combined company's proprietary products or regulatory enforcement
actions by FDA concerning its marketing practices would have a material adverse
effect on its business, financial condition and results of operations.


THE COMBINED COMPANY MAY NOT BE ABLE TO PROTECT ITS INTELLECTUAL PROPERTY.

The combined company's success will depend, in part, on its ability to obtain
and enforce patents, protect trade secrets, obtain licenses to technology owned
by third parties, when necessary, and conduct its business without infringing
upon the proprietary rights of others. The patent positions of pharmaceutical
firms, including the combined company's, can be uncertain and involve complex
legal and factual questions. In addition, the coverage sought in a patent
application may not be obtained or may be significantly reduced before the
patent is issued. Consequently, Celgene does not know whether any of the
combined company's pending applications, or any pending application the company
has licensed in from third parties, will result in the issuance of patents or,
if any patents are issued, whether they will provide significant proprietary
protection or commercial advantage. Since, under the current patent laws, patent
applications in the United States are maintained in secrecy until patents issue,
and since publications of discoveries in the scientific and patent literature
often lag behind actual discoveries, the combined company cannot be certain that
it was, or that the third parties from whom it has licensed patents or patent
applications were, the first to make the inventions covered by the patents and
patent applications in which the combined company has rights, or that such
patents and patent applications were the first to be filed on such inventions.
In the event that a third party has also filed a patent application for any of
the inventions described in the combined company's patents or patent
applications, or those it has licensed-in, the combined company could become
involved in an interference proceeding declared by the United States Patent and
Trademark Office to determine priority of invention. Such an interference could
result in the loss of a United States patent or loss of any opportunity to
secure United States patent protection for that invention. Even if the eventual
outcome is favorable to the combined company, such interference proceedings
could result in substantial cost to Celgene. Moreover, different countries have
different procedures for obtaining patents, and patents issued in different
countries provide different degrees of protection against the use of a patented
invention by others. There can be no assurance, therefore, that the issuance to
the combined company or its licensor, in a given country, of a patent covering
an invention will be followed by the issuance, in other countries, of patents
covering the same invention, or that any judicial interpretation of the
validity, enforceability or scope of the claims in a patent issued in one
country will be similar to the judicial interpretation given to the
corresponding patent issued in another country. Furthermore, even if the
combined company's patents, or those it has license in, are found valid and
enforceable, there can be no assurance that competitors will not be able to
design around such patents and compete with us using the resulting alternative
technology. If any of the combined company's issued or licensed patents are
infringed, we cannot guarantee that the combined company will be successful in
enforcing its intellectual property rights. Moreover, Celgene cannot assure you
that the combined company can successfully defend against any patent
infringement suit that may be brought against it by a third party. Patent
infringement lawsuits in the pharmaceutical and biotechnology industries can be
complex, lengthy and costly to both parties. An adverse outcome in such a
litigation could cause the combined company to lose exclusivity relating to the
subject matter delineated by such patent claims and may have a material adverse
effect on our business. If a third party is found to have rights covering
products or processes used by the combined company, we could be forced to cease
using these products or processes, subject to significant liabilities to such
third party and/or required to license technologies from such third party.
Further, the combined company relies upon unpatented proprietary and trade


                                       25
<PAGE>

secret technology that it tries to protect, in part, by confidentiality
agreements with its collaborative partners, employees, consultants, outside
scientific collaborators, sponsored researchers and other advisors. Celgene
cannot assure you that these agreements will not be breached or that the
combined company would have adequate remedies for any such breach. Celgene
cannot assure you that, despite precautions taken by the combined company,
others have not and will not obtain access to its proprietary technology or that
such technology will not be found to be non-proprietary or not a trade secret.
The combined company's right to practice the inventions claimed in some patents
which relate to THALOMID arises under licenses granted to Celgene by others,
including The Rockefeller University and EntreMed, Inc. While Celgene believes
these agreements to be valid and enforceable, Celgene cannot assure you that the
combined company's rights under these agreements will continue or that disputes
concerning these agreement will not arise. In addition, certain of the grants
contained in the licenses granted to Celgene depend upon the validity and
enforceability of other agreements to which Celgene is not a party.


THE PHARMACEUTICAL AND AGROCHEMICAL INDUSTRIES ARE HIGHLY COMPETITIVE AND
SUBJECT TO RAPID AND SIGNIFICANT TECHNOLOGICAL CHANGE.

The pharmaceutical and agrochemical industries in which Celgene operates, and
the combined company will operate, are highly competitive and subject to rapid
and significant technological change. The combined company's present and
potential competitors include major chemical and pharmaceutical companies, as
well as specialized pharmaceutical firms. Most of these companies have
considerably greater financial, technical and marketing resources than the
combined company. The combined company also experiences competition from
universities and other research institutions and, in some instances, competes
with others in acquiring technology from these sources. The pharmaceutical and
agrochemical industries have undergone, and are expected to continue to undergo,
rapid and significant technological change, and we expect competition to
intensify as technical advances in each field are made and become more widely
known. The development of products or processes with significant advantages over
those that the combined company is seeking to develop could have a material
adverse effect on its business, financial condition and results of operations.


SALES OF THE COMBINED COMPANY'S PRODUCTS ARE DEPENDENT ON THIRD-PARTY
REIMBURSEMENT.

Sales of the combined company's products will depend, in part, on the extent to
which the costs of its products will be paid by health maintenance, managed
care, pharmacy benefit and similar health care management organizations, or
reimbursed by government health administration authorities, private health
coverage insurers and other third-party payors. These health care management
organizations and third-party payors are increasingly challenging the prices
charged for medical products and services. Additionally, the containment of
health care costs has become a priority of federal and state governments, and
the prices of drugs have been targeted in this effort. We cannot assure you that
the combined company's products will be considered cost effective by payors,
that reimbursement will be available or, if available, that the level of
reimbursement will be sufficient to allow the combined company to sell its
products on a profitable basis.


                       RISKS RELATING TO SIGNAL'S BUSINESS

If the merger is approved and the merger agreement adopted, Signal will become a
wholly-owned subsidiary of Celgene. You should review the following risk factors
relating to Signal's business, since any negative factors affecting Signal after
the merger could affect Celgene's financial condition and could cause the market
price of Celgene's common stock to decline.

IF SIGNAL CONTINUES TO INCUR OPERATING LOSSES FOR LONGER THAN IT ANTICIPATES, IT
MAY NEVER BE PROFITABLE

Signal has generated operating losses since its inception in 1992 and as of
March 31, 2000 had an accumulated deficit of approximately $41.3 million. Signal
expects to continue to incur significant operating losses for the foreseeable
future as it continues to incur increasing costs related to research and
development, expansion of its operations and initiation of clinical trials.
Payments, if any, from Signal's corporate collaborators, interest income and
governmental grants are expected


                                       26
<PAGE>

to be its only sources of revenue for the foreseeable future. As of March 31,
2000, Signal has not received any significant milestone revenue and has received
license fees and research and development payments of $43.3 million. Revenue
from commercial sales of products based upon any drug target or drug lead that
Signal may identify is not expected for a number of years, if at all. Any such
revenue will depend on Signal's ability, alone or with others, to successfully
research, develop, obtain regulatory clearance for, manufacture and market its
products under development. The extent of Signal's future losses may exceed its
expectations and jeopardize its ability to become a profitable business.


BECAUSE SIGNAL'S DRUG CANDIDATES ARE AT AN EARLY STAGE OF DEVELOPMENT, THERE IS
A HIGH RISK OF FAILURE.

Signal has no products that have received regulatory clearance for commercial
sale. In addition, Signal has no compounds in human testing, referred to as
clinical trials. All of its compounds are in the research or preclinical
development stage, and Signal faces the risks of failure inherent in researching
and developing drugs based on new technologies. None of Signal's compounds may
ever enter clinical trials, be commercialized or generate revenue in the future.


THE DRUG DISCOVERY AND DEVELOPMENT PROCESS IS HIGHLY SPECULATIVE AND SIGNAL, OR
ITS COLLABORATORS WORKING WITH SIGNAL, MAY NEVER CREATE A COMMERCIAL DRUG.

The discovery and development of new drugs is highly uncertain and subject to a
number of significant risks that could prevent Signal or its collaborators from
ever creating a commercial drug. Drug leads and drug candidates that appear to
be promising at early stages of development may not enter clinical development
or reach the market for a number of reasons, including the possibilities that
the drug leads and drug candidates will:

o be found ineffective or cause harmful side effects during preclinical testing
  or clinical trials;

o fail to receive necessary regulatory clearance;

o be difficult or expensive to manufacture on a commercial scale; or

o fail to generate market demand.

Signal's current and potential discoveries of the gene regulating pathways
associated with specific diseases may not lead to the development or
commercialization of drugs.

To date, none of the compounds generated by Signal or through its collaborations
has been approved for clinical testing.  None may ever be submitted for clinical
testing.  If Signal identifies any potential products,  either  independently or
through its collaborations, they will face the following risks:

o its discovery and development programs may not be successfully initiated or
  completed;

o any IND Signal files may not be accepted by the FDA or other applicable
  regulatory authorities;

o clinical trials may not commence or be completed as planned;

o required regulatory clearance may not be obtained on a timely basis, if at
  all; or

o any products for which clearance is obtained may not be commercially
  successful.

In addition, success in preclinical testing and early stage clinical trials does
not ensure that later clinical trials will be successful.


IF SIGNAL CANNOT MAINTAIN ITS CURRENT CORPORATE COLLABORATIONS OR ENTER INTO NEW
CORPORATE COLLABORATIONS, SIGNAL MAY NEVER DEVELOP OR COMMERCIALIZE PRODUCTS OR
ACHIEVE PROFITABILITY.

Signal relies, to a significant extent, on its corporate collaborators to
provide funding that supports its research and to conduct some research,
preclinical and clinical development, manufacturing and marketing. As of March
31, 2000, approximately 90% of the revenue that Signal has received has been
from its collaborations. Signal expects that a similar percentage of its revenue
for the


                                       27
<PAGE>

foreseeable future will be generated by collaborations. If any of Signal's
corporate collaborators were to breach or terminate their agreement with Signal
or otherwise fail to conduct their collaborative activities successfully and in
a timely manner, the preclinical or clinical development or commercialization of
the affected drug candidates or research programs could be delayed or
terminated. In addition, Signal expects to rely on its corporate collaborators
for commercialization of some of Signal's products.


Signal's ability to continue to fund its research and development programs,
maintain adequate capital reserves and, ultimately, achieve profitability will
be dependent upon its and its collaborators' ability to achieve specified
milestones under existing collaborations with Serono, Axys, DuPont
Pharmaceuticals, Byk Gulden and Pliva or Signal's ability to enter into
additional collaborations. Signal has not yet entered into collaborations for a
number of its existing or prospective programs. Even if a potential collaborator
believes that Signal's technologies and research discoveries justify entering
into an agreement with Signal, its budgeting cycle, resources or other
priorities may not permit a timely collaboration. Signal also must compete with
other companies for the limited number of existing opportunities to enter into
collaborative arrangements.


Signal may not be able to negotiate additional collaborative agreements in the
future on acceptable terms, if at all. In particular, potential collaborators
may be unwilling to enter into an agreement that allows Signal to retain rights
in its focus areas of cancer and inflammatory disease. In addition, current or
future collaborative agreements may not be successful. Finally, current or
future collaborators may pursue or develop alternative technologies either on
their own or in collaboration with others, including Signal's competitors. In
the absence of such collaborative agreements, Signal may be required to delay or
curtail its research and development activities to a significant extent.


As of March 31, 2000, Signal has not received any significant milestone revenue
and has received license fees and research and development payments of $43.3
million. These payments have not covered all of the expenses incurred in
conducting Signal's business. Signal's future revenue will depend in part on its
ability to receive milestone payments and royalties triggered by the continued
development and commercialization of drugs by its collaborators, over which
Signal has little or no control.


Signal currently has arrangements with five corporate collaborators: Serono,
Axys Pharmaceuticals, Byk Gulden, Pliva and DuPont Pharmaceuticals. If one of
these collaborators were to terminate its arrangement with Signal, it could
cause a substantial decrease in its revenue as well as potential delay or
curtailment of ongoing research and development activities. In general, Signal's
collaborations may be terminated upon a breach by either party. In particular,
the agreement with Serono may be terminated by a party upon a merger of the
other party. Moreover, some of Signal's collaborations may be terminated by its
collaborators if Signal fails to achieve specified research and development
milestones. Signal has in the past encountered, and may in the future encounter,
difficulty in satisfying some stated milestones under its collaboration
agreements.


Some of Signal's corporate or academic collaborators are conducting multiple
drug discovery and development efforts within each disease area that is the
subject of the collaboration with Signal. Generally, in each of Signal's
collaborations, Signal has agreed not to conduct independently, or with any
third party, any research that is in conflict with the rights granted under the
collaboration agreement. Signal's collaborations may have the effect of limiting
the areas of research and development that it may pursue.


BECAUSE SIGNAL EXPECTS TO GENERATE A SIGNIFICANT PERCENTAGE OF ITS FUTURE
REVENUES FROM CO-COMMERCIALIZATION AND PROFIT-SHARING ARRANGEMENTS, THE SUCCESS
OR FAILURE OF THESE ARRANGEMENTS WILL SIGNIFICANTLY IMPACT SIGNAL'S FUTURE
FINANCIAL RESULTS.


Under three of Signal's current collaborations, Signal has co-commercialization
or profit-sharing rights, and Signal will attempt to enter into additional
collaborations that provide Signal with similar rights. Because these types of
arrangements are expected to generate a larger percentage of Signal's future
revenues as compared with collaborations under which it receives only royalties,
these


                                       28
<PAGE>

collaborations may disproportionately affect Signal's financial success. If
these collaborations are not successful, or if Signal decides to abandon or
license some or all of these co-commercialization or profit-sharing rights to
third parties, Signal may not achieve all of its financial objectives.


SIGNAL'S COMPETITORS MAY BE ABLE TO DEVELOP AND MARKET PRODUCTS MORE QUICKLY OR
THAT ARE MORE EFFECTIVE THAN SIGNAL'S, WHICH WOULD REDUCE OR ELIMINATE ITS
COMMERCIAL OPPORTUNITY.


The competition among pharmaceutical and biotechnology companies to identify
drug targets and drug candidates for development is intense and is expected to
increase. Signal's commercial opportunity will be reduced or eliminated if its
competitors develop and market products more quickly or that are more effective,
have fewer side effects, are easier to administer or are less expensive than
Signal's product candidates. Other companies have product candidates in clinical
trials to treat most of the diseases for which Signal is seeking to discover and
develop product candidates. Even if Signal or its collaborators are successful
in developing effective drugs, Signal's products may not compete effectively
with these products or other successful products.


In  addition,  Signal's  competitors  include  fully  integrated  pharmaceutical
companies, biotechnology companies, universities and public and private research
institutions that have substantially greater capital resources,  larger research
and development  staffs and facilities,  greater  experience in drug development
and in obtaining  regulatory  clearance and greater  manufacturing and marketing
capabilities than Signal does. These organizations also compete with Signal to:


o attract qualified personnel;


o attract parties for acquisitions, joint ventures or other collaborations; and



o license the proprietary technology of institutions that is competitive with
  the technology Signal is developing and applying.


BECAUSE SIGNAL MUST OBTAIN REGULATORY CLEARANCE TO TEST AND MARKET ITS PRODUCTS
IN THE UNITED STATES AND FOREIGN JURISDICTIONS, SIGNAL CANNOT PREDICT WHETHER OR
WHEN IT WILL BE PERMITTED TO COMMERCIALIZE ITS PRODUCTS.


The pharmaceutical industry is subject to stringent regulation by a wide range
of authorities in the geographic areas where Signal intends to develop and
commercialize products. A pharmaceutical product cannot be marketed in the
United States until it has completed rigorous preclinical testing and clinical
trials and an extensive regulatory clearance process implemented by the FDA.
Satisfaction of regulatory requirements typically takes many years, is dependent
upon the type, complexity and novelty of the product and requires the
expenditure of substantial resources.


Before commencing clinical trials in humans, Signal must submit and receive
clearance from the FDA by means of an IND application. Clinical trials are
subject to oversight by institutional review boards and the FDA and:


o must be conducted in conformance with the FDA's good laboratory practice
  regulations;

o must meet requirements for institutional review board oversight;

o must meet requirements for informed consent;

o must meet requirements for good clinical and manufacturing practices;

o are subject to continuing FDA oversight;

o may require large numbers of test subjects; and

o may be suspended by Signal or the FDA at any time if it is believed that the
  subjects participating in these trials are being exposed to unacceptable
  health risks or if the FDA finds deficiencies in the IND application or the
  conduct of these trials.


                                       29
<PAGE>

Before receiving FDA clearance to market a product, Signal must demonstrate that
the product is safe and effective on the patient population that will be
treated. Data obtained from preclinical and clinical activities are susceptible
to varying interpretations that could delay, limit or prevent regulatory
clearances. Additionally, Signal has limited experience in conducting and
managing the clinical trials and manufacturing processes necessary to obtain
regulatory clearance.

If regulatory clearance of a product is granted, this clearance will be limited
to those disease states and conditions for which the product is demonstrated
through clinical trials to be safe and efficacious. Signal cannot ensure that
any compound developed by it, alone or with others, will prove to be safe and
efficacious in clinical trials and will meet all of the applicable regulatory
requirements needed to receive marketing clearance.

Outside the United States, Signal's ability to market a product is contingent
upon receiving a marketing authorization from the appropriate regulatory
authorities. This foreign regulatory approval process includes all of the risks
associated with FDA clearance described above.


SIGNAL EXPECTS THAT ITS QUARTERLY RESULTS OF OPERATIONS WILL FLUCTUATE, WHICH
MAY MAKE IT DIFFICULT TO PREDICT THE COMBINED COMPANY'S FUTURE PERFORMANCE.

Signal's quarterly operating results have fluctuated in the past and are likely
to do so in the future. If revenue declines or does not grow as anticipated,
Signal may not be able to correspondingly reduce its operating expenses. A large
portion of Signal's expenses, including expenses for facilities, equipment,
contracted research and personnel, is relatively fixed. In addition, Signal is
significantly increasing operating expenses in 2000. Failure to achieve
anticipated levels of revenue could therefore significantly harm Signal's
operating results for a particular fiscal period. Due to the possibility of
fluctuations in Signal's revenue and expenses, Signal believes that
quarter-to-quarter comparisons of its operating results are not a good
indication of its future performance. Some of the factors that could cause
Signal's operating results to fluctuate include:

o termination or reduction in the scope of Signal's corporate collaborations;

o the success rate of Signal's discovery and development efforts associated with
  milestones and royalties;

o Signal's ability to enter into new agreements with corporate collaborators or
  to extend the terms of its existing corporate collaboration agreements;

o Signal's ability to satisfy all applicable regulatory requirements; and

o general and industry-specific economic conditions that may affect Signal's
  corporate collaborators' research and development expenditures.


IF SIGNAL'S TECHNOLOGIES OR THOSE OF ITS COLLABORATORS ARE ALLEGED OR FOUND TO
INFRINGE THE PATENTS OR PROPRIETARY RIGHTS OF OTHERS, SIGNAL MAY BE SUED, MAY
HAVE TO LICENSE THOSE RIGHTS FROM OTHERS ON UNFAVORABLE TERMS OR MAY CEASE
ACTIVITY.

Signal's commercial success will depend significantly on its ability to operate
without infringing the patents and proprietary rights of third parties. Signal's
technologies along with its licensors' and its collaborators' technologies may
infringe the patents or proprietary rights of others. An adverse outcome in
litigation or an interference to determine priority or other proceeding in a
court or patent office could subject us to significant liabilities, require
disputed rights to be licensed from or to other parties or require Signal, its
licensors or its collaborators to cease using a technology necessary to carry
out research, development and commercialization.

Litigation to challenge the validity of patents, to defend against patent
infringement claims of others or to assert infringement claims against others
can be expensive and time consuming, even if the outcome is favorable. An
outcome of any patent prosecution or litigation that is unfavorable to Signal or
one of its licensors or collaborators may have a material adverse effect on
Signal. Signal could incur substantial costs if its is required to defend itself
in patent suits brought by third parties, if Signal participates in patent suits
brought against or initiated by its licensors or collaborators or if


                                       30
<PAGE>

Signal initiate such suits. Signal may not have sufficient funds or resources in
the event of litigation. Additionally, Signal may not prevail in any such
action, or, even if Signal prevails, the cost may have a material adverse affect
on Signal.

A number of pharmaceutical companies, biotechnology companies, independent
researchers, universities and research institutions may have filed patent
applications or may have been granted patents that cover technologies similar to
the technologies owned, optioned by or licensed to Signal or its collaborators.
For instance, a number of patents may have been issued or may be issued in the
future on targets or their use in screens for evaluating the activity of
compounds on a specific drug target, called screening assays, that could prevent
Signal and its collaborators from developing screens using such targets,
compounds relating to such targets or relating to other aspects of technology
that Signal uses or expects to use. In addition, since United States patents are
secret until issued, Signal is unable to determine all of the patents or patent
applications that may materially affect its or its collaborators' ability to
make, use or sell any potential products.

Signal is aware of three issued United States patents relating to specific
methods for regulating gene expression. Signal may in the future have to prove
it is not infringing these patents or be required to obtain licenses to one or
more of these patents, and Signal does not know whether such licenses will be
available on commercially reasonable terms, or at all. Signal is also aware of a
United States patent which has been issued to a third party claiming subject
matter relating to the NF-kB pathway which appears to overlap with technology
claimed in some of its pending NF-kB patent applications. Signal believes that
one or more interference proceedings will be initiated by the U.S. Patent and
Trademark Office to determine priority of invention for this subject matter.
Signal cannot be certain of the outcome of any such proceedings. An adverse
outcome may have a material adverse effect on Signal. Even if Signal were to
prevail, this proceeding may have an adverse impact on Signal because such
proceedings are complex and costly.

Any conflicts resulting from third-party patent applications and patents could
significantly reduce the coverage of the patents owned, optioned by or licensed
to Signal or its collaborators and limit its ability or that of its
collaborators to obtain meaningful patent protection. If patents are issued to
third parties that contain competitive or conflicting claims, Signal, its
licensors or its collaborators may be legally prohibited from pursuing research,
development or commercialization of potential products or be required to obtain
licenses to these patents or to develop or obtain alternative technology.
Signal, its licensors and or its collaborators may be legally prohibited from
using patented technology, may not be able to obtain any license to the patents
and technologies of third parties on acceptable terms, if at all, or may not be
able to obtain or develop alternative technologies.

In addition, like many biopharmaceutical companies, Signal may from time to time
hire scientific personnel formerly employed by other companies involved in one
or more areas similar to the activities conducted by Signal. Signal or these
individuals may be subject to allegations of trade secret misappropriation or
other similar claims as a result of their prior affiliations.


SIGNAL'S ABILITY TO COMPETE MAY DECREASE IF IT DOES NOT ADEQUATELY PROTECT ITS
INTELLECTUAL PROPERTY RIGHTS.

Signal's commercial success will depend in part on Signal's and its
collaborators' ability to obtain and maintain patent protection for Signal's
proprietary technologies, drug targets and potential products and to effectively
preserve its trade secrets. Because of the substantial length of time and
expense associated with bringing potential products through the development and
regulatory clearance processes to reach the marketplace, the pharmaceutical
industry places considerable importance on obtaining patent and trade secret
protection. Signal seeks patent protection for its proprietary technology, drug
targets and potential products. However, the patent positions of pharmaceutical
and


                                       31
<PAGE>

biotechnology companies can be highly uncertain and involve complex legal and
factual questions. No consistent policy regarding the breadth of claims allowed
in biotechnology patents has emerged to date. Accordingly, Signal cannot predict
the type and breadth of claims allowed in these patents.


The degree of future protection for Signal's proprietary rights is uncertain.
Many factors may affect Signal's patent position, including whether:


o  Signal was the first to invent the inventions covered by each of its pending
   patent applications, and patents;


o  Signal was the first to file patent applications for these inventions;


o  others will independently develop similar or alternative technologies or
   duplicate any of Signal's technologies;


o  any of Signal's pending patent applications will result in issued patents;


o  any patents issued to Signal or its collaborators will provide a basis for
   commercially viable products, will provide Signal with any competitive
   advantages or will not be challenged by third parties;


o  Signal's licensors prevail in any interference or related proceeding
   concerning Signal's licensed patents or licensed patent applications;


o  Signal will develop additional proprietary technologies that are patentable;
   or


o  the patents of others will have an adverse effect on Signal's ability to do
   business.


In addition to patent protection, Signal also relies on copyright protection,
trade secrets, know-how, continuing technological innovation and licensing
opportunities. Signal attempts to require its employees, consultants and some
collaborators to execute confidentiality and invention assignment agreements
upon commencement of a relationship with it; however, these agreements may not
provide meaningful protection for its trade secrets, confidential information or
inventions in the event of unauthorized use or disclosure of such information,
and adequate remedies may not exist in the event of such unauthorized use or
disclosure.


IF SIGNAL LOSES ITS KEY PERSONNEL OR IS UNABLE TO ATTRACT AND RETAIN QUALIFIED
PERSONNEL AS NECESSARY, IT COULD DELAY OR IMPAIR THE QUALITY OF SIGNAL'S PRODUCT
DEVELOPMENT PROGRAMS AND RESULT IN REDUCED RESEARCH AND DEVELOPMENT EFFORTS.


Signal's success is highly dependent on the principal members of its scientific
and management staff, as well as it's scientific advisors and consultants. If
Signal loses the services of one or more of these individuals, it could prevent
Signal from advancing its technology, developing potential products or achieving
profitability. Signal may not be able to attract or retain qualified employees
in the future due to the intense competition for qualified personnel among
biotechnology and other technology-based businesses, particularly in the San
Diego area. If Signal is not able to attract and retain the necessary personnel
to accomplish its business objectives, Signal may experience constraints that
will adversely affect its ability to meet the demands of its collaborators in a
timely fashion or to support its internal research and development programs. In
particular, Signal's product development programs depend on its ability to
attract and retain highly skilled scientists, including molecular biologists,
biochemists and engineers, and clinical and regulatory experts. Signal's
employees are "at-will" which means they may quit at any time and Signal may
fire them at any time.


Signal's planned activities will require additional expertise in specific
industries and areas applicable to the products developed through its
technologies. These activities will require the addition of new personnel,
including management, and the development of additional expertise by existing
management personnel.


                                       32
<PAGE>

SIGNAL DEPENDS ON THIRD PARTIES TO PERFORM MANY PRECLINICAL AND CLINICAL
DEVELOPMENT ACTIVITIES, AND ITS DEVELOPMENT PROGRAMS MAY BE DELAYED OR
TERMINATED IF THEY FAIL TO PERFORM THEIR RESPONSIBILITIES COMPLETELY AND ON
TIME.

Signal relies and will continue to rely in part on third parties to perform
preclinical and clinical development activities. Specifically, Signal expects to
contract with third parties for the manufacture of drug product, the conduct of
preclinical animal studies, including studies regarding biological activity,
safety, absorption, metabolism and elimination of drug candidates, and the
performance of clinical trials for safety and efficacy in humans. Signal's
agreements for contract preclinical and clinical development services place
substantial responsibilities on third parties for development of its drug
candidates which could result in delays in or termination of development if
these third parties fail to perform as expected. Signal may not be able to
maintain any of these existing relationships, or establish new ones on favorable
terms, if at all. Signal may not be able to enter into these arrangements
without undue delays or excessive expenditures. Furthermore, these third parties
may not perform as expected.


SIGNAL HAS NO MANUFACTURING EXPERIENCE AND MUST RELY ON THIRD-PARTY
MANUFACTURING.

To date, Signal has not manufactured any products for preclinical, clinical or
commercial purposes and does not have any manufacturing facilities. Signal
currently uses third-party contract manufacturers, and may in the future use its
corporate collaborators, for the production of materials for preclinical and
clinical trials and for the manufacture of future products for
commercialization. If Signal is unable to secure such outside manufacturing
capabilities, Signal will not be able to conduct preclinical product
development, clinical trials or commercialize its potential products as planned.


SIGNAL'S BUSINESS INVOLVES THE USE OF HAZARDOUS MATERIALS WHICH COULD CAUSE
SIGNAL TO INCUR SUBSTANTIAL COSTS IN THE EVENT SUCH MATERIALS ARE NOT STORED,
HANDLED OR DISPOSED OF CORRECTLY.

Signal's research and development processes involve the controlled use of
hazardous materials, including infectious biological materials, chemicals and
various radioactive compounds. Signal is subject to federal, state and local
laws and regulations governing the use, manufacture, storage, handling and
disposal of hazardous materials and waste products. The risk of accidental
contamination or injury from these materials cannot be completely eliminated. In
the event of an accident, Signal could be held liable for any damages that
result and any such liability could exceed its resources and result in lengthy
interruption of business operations. If an accident occurred, Signal would
likely incur significant costs to comply with environmental laws and regulations
in the future.


SIGNAL MAY BE SUED FOR PRODUCT LIABILITY AND ITS INSURANCE COVERAGE MAY NOT BE
SUFFICIENT.

Signal may be held liable if any product Signal or its collaborators develop, or
any product which is made with the use of any of Signal's technologies, causes
injury or is found otherwise unsuitable during product testing, manufacturing,
marketing or sale. Signal currently has no product liability insurance. When
Signal attempts to obtain product liability insurance, this insurance may be
expensive, or may not fully cover its potential liabilities. Inability to obtain
sufficient insurance coverage at an acceptable cost or otherwise to protect
against potential product liability claims could prevent or inhibit the
commercialization of products developed by Signal or its collaborators. If
Signal is sued for any injury caused by its products, Signal's liability could
exceed its total assets.


                                       33
<PAGE>

                                  THE COMPANIES


CELGENE CORPORATION

Celgene Corporation, headquartered in Warren, New Jersey, is an independent
biopharmaceutical company engaged in the discovery, development and
commercialization of small molecule drugs for the treatment of cancer and
immunological diseases. Celgene's lead drug THALOMID(Reg. TM) received approval
from the FDA in 1998 for the treatment of ENL. Sales of THALOMID have been
rising rapidly and were $11.7 million in the first quarter of this year. Over
140 clinical trials are being conducted to determine the drug's potential
efficacy in a variety of cancer and inflammatory conditions.

Celgene's chiral program has developed a chirally pure version of Ritalin, the
market standard treatment for the symptoms of Attention Deficit Disorder and
Attention Deficit Hyperactivity Disorder. This drug is the subject of a major
strategic alliance between Celgene and Novartis Pharma AG, and has completed all
regulatory trials. A New Drug Application will be submitted later this year.

Celgene's oncology and immunology pipeline is highlighted by two classes of
novel, proprietary small molecule compounds. Selective Cytokine Inhibitory Drugs
or SelCIDs(TM) are potent inhibitors of tumor necrosis factor alpha or TNF-.
They act through the selective inhibition of the enzyme Phosphodiesterase 4 or
PDE 4. Preclinical and animal studies have shown this class of compounds to be
significantly more active immunomodulators than THALOMID. The lead SelCID was
found to be well tolerated in Phase I trials. A pilot double blind,
placebo-controlled Phase II trial in Crohn's disease has recently been expanded
based on blinded positive responses. Additional trials in a wide range of
disease states will be initiated over the next twelve months for Celgene's lead
SelCID and the follow-on compounds.

The IMiDs(TM) or Immunomodulatory Drugs are a class of novel structural
analogues of thalidomide which have been demonstrated in preclinical tests to be
substantially more potent than thalidomide. Two lead IMiDs have completed
initial Phase I trials and were found to be well tolerated and nonsedating.
Phase I/II trials in multiple myeloma patients are scheduled to begin in the
next sixty days. It was recently announced that Celgene and the National Cancer
Institute have entered into a letter of intent regarding a major research
collaboration for the preclinical and clinical study of this class of compounds.

The U.S. Patent and Trademark Office has issued Celgene numerous composition of
matter and use patents relating to Celgene's SelCIDs and IMiDs.


SIGNAL PHARMAEUTICALS, INC.

Signal Pharmaceuticals, Inc., headquartered in San Diego, California, is a
biopharmaceutical company focused on discovering and developing new classes of
small molecule drugs that regulate disease-associated genes.

Signal has developed and integrated a platform of target and drug discovery
technologies to accelerate the application of genomics to the discovery of
important new classes of gene regulating drugs. Signal's target and drug
discovery engine has enabled it to successfully identify gene regulating targets
and drug leads across six major classes of disease. Signal's drug pipeline
includes eight major drug discovery and development programs in the fields of
cancer, inflammation, bone metabolism, neurological and cardiovascular disease
and virology. Signal's SERM program has identified drug leads with potential for
preventing and treating breast, prostate and other cancers, in addition to
preventing and treating osteoporosis.

Signal's JNK program has generated drug leads that have demonstrated significant
disease-modifying  activity in a  preclinical  arthritis  model.  Because  these
compounds  are  potent  and  selective  regulators  of the TNF,  IL-2 and  gamma
interferon gene pathways, they may have broad clinical utility in


                                       34
<PAGE>

treating arthritis, stroke, cancer and other diseases. Signal also has
identified potent and selective inhibitors of the NF-k(beta) pathway that
regulates cytokine genes (e.g., IL-1, IL-2, IL-6, IL-8 and TNF), and play a
pivotal role in immune-inflammatory diseases, cardiovascular diseases and
cancer.

Signal researchers also are identifying new gene regulating molecules within
cells that provide a sustainable pipeline of drug targets for future drug
discovery programs. Signal conducts these discovery programs both independently
and in collaboration with leading academic researchers and pharmaceutical
partners.


                                       35
<PAGE>

                           THE SIGNAL SPECIAL MEETING


DATE, TIME AND PLACE OF SPECIAL MEETING

This proxy statement/prospectus is being furnished to the holders of Signal
common stock and preferred stock in connection with the solicitation of proxies
by the Signal board for use at the Signal special meeting to be held at Signal's
principal offices, located at 5555 Oberlin Drive, San Diego, California, on ,
2000 at local time, and any adjournment or postponement of that meeting.


MATTERS TO BE CONSIDERED AT THE SIGNAL SPECIAL MEETING

At the Signal special meeting, Signal shareholders will be asked to consider and
vote upon:

   o the approval and adoption of the merger agreement and the approval of the
     principal terms of the merger;

   o with respect to the holders of Signal preferred stock, approval of the
     conversion of all outstanding shares of Signal preferred stock into Signal
     common stock effective immediately prior to the effective time of the
     merger; and

   o such other matters as may be properly brought before the meeting, or any
     adjournment or postponement thereof.


SIGNAL BOARD RECOMMENDATION

The Signal board of directors unanimously approved the merger agreement and the
merger and unanimously recommends a vote for approval of the merger proposal and
the preferred stock conversion proposal.


VOTES REQUIRED AND OUTSTANDING SHARES

The approval of the merger proposal requires the affirmative vote of the holders
of a majority of the outstanding shares of Signal common stock and a majority of
the outstanding shares of Signal preferred stock, each voting as a separate
class. The approval of the preferred stock conversion proposal requires the
affirmative vote of 75% of the outstanding shares of Signal preferred stock. In
addition, under the terms of the merger agreement, in order for the merger to
occur, the holders of no more than 5% of the outstanding shares of Signal may
have perfected or be entitled to exercise dissenter's rights under Chapter 13 of
the California General Corporation Law.

Only holders of record of Signal common stock and  preferred  stock at the close
of  business  on , 2000 will be  entitled to notice of and to vote at the Signal
special meeting. At the close of business on the record date there were
     shares  of  Signal  common  stock and  shares  of  Signal  preferred  stock
outstanding  and entitled to vote.  Each holder of record of Signal common stock
on the  record  date will be  entitled  to one vote for each  share  held on all
matters to be voted upon at the Signal special meeting. In addition, the holders
of Signal  preferred stock will be entitled to one vote for each share of Signal
common stock into which such preferred stock is convertible on all matters to be
voted upon at the Signal special meeting.

Except for the shareholders identified herein under "Management and Other
Information Relating to Signal--Preferred Stockholders of Signal," as of the
record date, to the knowledge of Signal, no other person beneficially owned more
than 5% of the outstanding Signal common stock or preferred stock.


QUORUM AND ABSTENTIONS

The presence, in person or by properly executed proxy, of the holders of a
majority of the shares entitled to vote at the Signal special meeting is
necessary to constitute a quorum. Abstentions will be counted for purposes of
determining a quorum. For purposes of obtaining the required vote of a majority
of the outstanding shares for approval and adoption of the merger agreement and
the


                                       36
<PAGE>

approval of the principal terms of the merger, the effect of an abstention will
be the same as a vote against the proposal. Abstentions will not be counted for
any purpose in determining approval of the conversion of the Signal preferred
stock into Signal common stock.


VOTING OF PROXIES

All shares of Signal common stock and preferred stock that are entitled to vote
and are represented at the Signal special meeting by properly executed proxies
received prior to or at the Signal special meeting, and not revoked, will be
voted at the Signal special meeting in accordance with the instructions
indicated on such proxies. If no instructions are indicated, such proxies will
be voted for approval of the merger proposal and for approval of the preferred
stock conversion proposal.


REVOCABILITY OF PROXIES

Any person giving a proxy pursuant to this solicitation has the power to revoke
it at any time before it is voted. It may be revoked by filing with the
corporate secretary of Signal at Signal's principal offices, a written notice of
revocation or a duly executed proxy bearing a later date, or it may be revoked
by attending the meeting and voting in person. Attendance at the meeting will
not, by itself, revoke a proxy.

Notwithstanding the preceding section, no shareholder who has entered into a
voting and proxy agreement with Celgene may revoke his, her or its irrevocable
proxy. A copy of a form of the voting and proxy agreement is attached to this
proxy statement/prospectus as Exhibit E to Appendix A.


SOLICITATION

This prospectus/proxy statement was mailed to all Signal shareholders of record
as of the record date and constitutes notice of the Signal special meeting in
conformity with the requirements of California law. The cost of the solicitation
of proxies from holders of Signal common and preferred stock and all related
solicitation costs will be borne by Signal. In addition, Signal may reimburse
brokerage firms and other persons representing beneficial owners of shares for
their expenses in forwarding solicitation materials to such beneficial owners.
Original solicitation of proxies by mail may be supplemented by telephone,
telegram or personal solicitation by directors, officers or other regular
employees of Signal. No additional compensation will be paid to directors,
officers or other regular employees for such services.


VOTING AND PROXY AGREEMENTS

Pursuant to voting and proxy agreements dated June 29, 2000, between Celgene and
certain shareholders of Signal, these shareholders have granted Celgene an
irrevocable proxy to vote all of their Signal shares in favor of the approval
and adoption of the merger agreement and the approval of the principal terms of
the merger and, where applicable, in favor of the conversion of the Signal
preferred stock into Signal common stock. As of the record date, these
shareholders owned shares representing approximately 56% of the outstanding
shares of Signal common stock and approximately 79% of Signal preferred stock
entitled to vote at the Signal special meeting. Accordingly, Celgene has
sufficient voting power to constitute a quorum and to approve all matters to be
considered at the Signal special meeting, regardless of the vote of any other
shareholder. Celgene has agreed to vote all shares of Signal common stock and
Signal preferred stock subject to such voting and proxy agreements in favor of
the merger proposal and the preferred stock conversion proposal.

Holders of Signal capital stock should not send any certificates representing
Signal capital stock with the enclosed proxy card. If the merger is approved, a
letter of transmittal will be mailed after the effective time of the merger to
each person who is a holder of outstanding Signal capital stock immediately
before the effective time. Signal shareholders should send certificates
representing Signal capital stock to the exchange agent only after they receive
the instructions contained in the letter of transmittal and only in accordance
with those instructions.


                                       37
<PAGE>

                                   THE MERGER


GENERAL DESCRIPTION OF THE MERGER


THE MERGER. At the effective time, Celgene Acquisition Corp. will merge with and
into Signal. Signal will continue as the surviving corporation and become a
wholly-owned subsidiary of Celgene. At the effective time of the merger:


o  each outstanding share of Signal common stock (including shares of Signal
   preferred stock which will be converted into Signal common stock immediately
   before the merger), other than shares owned by holders who are exercising
   dissenters' rights under California law, will be converted into the right to
   receive 0.1257 of a share of Celgene common stock, par value $.01 per share;


o  each treasury share of Signal will be canceled;


o  each outstanding share of common stock of Celgene Acquisition Corp. will be
   converted into one share of common stock, no par value, of Signal, the
   surviving corporation in the merger; and


o  each option and warrant to purchase Signal common stock or Series C-1 or
   Series C-2 preferred stock outstanding immediately prior to the effective
   time of the merger, whether vested or unvested, will cease to represent a
   right to acquire shares of Signal common stock or Series C-1 or Series C-2
   preferred stock and will be converted, at the effective time of the merger,
   into an option or warrant to acquire, on the same terms and conditions, the
   number of shares of Celgene common stock determined by multiplying the number
   of shares of Signal common stock or Series C-1 or Series C-2 preferred stock
   subject to that Signal stock option or warrant by 0.1257, rounded down, if
   necessary, to the nearest whole share, at a price per share (rounded up to
   the nearest cent) equal to the per share exercise price specified in that
   Signal stock option or warrant divided by 0.1257.


No fractional shares of Celgene common stock will be issued in the merger;
instead, Signal shareholders will receive cash for the fraction of a share of
Celgene common stock they would have otherwise received. See "Conversion of
Shares; Procedures for Exchange of Certificates; No Fractional Shares."


BACKGROUND OF THE MERGER


During March and April 2000, representatives of Prudential Securities
Incorporated, Celgene's financial advisor, met with Dr. Sol J. Barer, Celgene's
president and chief operating officer, to discuss various strategic initiatives
available to Celgene. During these discussions, Prudential Securities suggested
that there might be a strong scientific fit between Celgene and Signal. On April
3, 2000, Dr. Barer telephoned Dr. Alan J. Lewis, Signal's president and chief
executive officer. At this time, Dr. Barer indicated Celgene's interest in
learning more about Signal's research programs and suggested that he and Dr.
Lewis arrange to meet during Dr. Lewis' next visit to the East Coast to discuss
the scientific and business progress of both companies. Dr. Barer noted that he
was aware that Signal had filed a registration statement with the SEC regarding
a proposed initial public offering of Signal's common stock and that Signal was
awaiting appropriate market conditions to begin roadshow presentations.


Prior to Dr. Barer's telephone call, Dr. Lewis had made plans to be in
Connecticut during the week of April 10, 2000 and suggested to Dr. Barer that
they meet for dinner on April 11, 2000. On April 11, 2000, Dr. Lewis met for
dinner with Dr. Barer and John W. Jackson, Celgene's chief executive officer, to
discuss various potential strategic transactions between Signal and Celgene,
including research collaborations, equity investments and acquisition
transactions. Dr. Lewis informed Dr. Barer and Mr. Jackson that the proposed
initial public offering was Signal's first priority at that time, and,
accordingly, the parties agreed to proceed with discussions regarding potential
research collaboration opportunities.


                                       38
<PAGE>

On April 18, 2000, at the meeting of Celgene's board of directors, also attended
by Proskauer Rose LLP, outside counsel to Celgene, and Robert J. Hugin,
Celgene's chief financial officer, Celgene's management presented an overview of
Signal to Celgene's board. Discussion at this meeting centered on the need for
Celgene to pursue a strategic transaction with a company like Signal.

On May 3, 2000, Dr. Lewis and Bradley B. Gordon, Signal's senior vice president
finance and chief financial officer, met with representatives of FleetBoston
Robertson Stephens Inc., or Robertson Stephens, Signal's lead underwriter in
connection with its proposed initial public offering, at Signal's headquarters
to discuss strategic financing options, including proceeding with the proposed
initial public offering and pursuing potential merger and acquisition
opportunities.

On May 17, 2000, at a regularly scheduled meeting of Signal's board of directors
attended by representatives of Robertson Stephens and Cooley Godward LLP,
Signal's outside legal counsel, Dr. Lewis informed the board of Celgene's
interest in pursuing a potential research collaboration with Signal.

On May 17 and May 18, 2000, Mr. Jackson, Dr. Barer, Dr. David Stirling,
Celgene's chief scientific officer, and Dr. Jerome B. Zeldis, Celgene's senior
vice president, medical affairs, visited Signal's facility in San Diego,
California. At this meeting, Dr. Lewis, Mr. Gordon, Dr. David W. Anderson,
Signal's senior vice president and chief scientific officer, and Douglas E.
Richards, Signal's vice president, corporate development, presented an overview
of Signal's business, with a particular emphasis on Signal's research programs
in cancer and inflammation as potentially attractive collaboration opportunities
for Celgene. Celgene's management also provided Signal's management with a brief
scientific and business overview regarding Celgene during this meeting.

On May 23, 2000, Dr. Barer telephoned Dr. Lewis to express Celgene's desire to
discuss a proposed acquisition of Signal by Celgene. In response to Dr. Barer's
call, Dr. Lewis called a telephonic special meeting of Signal's board of
directors on May 25, 2000, at which time Signal's board authorized officers of
Signal to proceed with discussions with Celgene regarding a potential merger.
Signal's board also authorized the officers to engage Robertson Stephens to act
as financial advisor to Signal in connection with such a transaction.

On May 25, 2000, Celgene and Signal entered into a mutual confidentiality
agreement to permit each company to obtain access to confidential information
about the other company.

During the period from May 25, 2000 to June 22, 2000, representatives of Celgene
and Signal and their respective financial and legal advisors conducted
substantial due diligence investigations of each other's business, intellectual
property and operations and further discussed the terms of a proposed merger.

On June 1, 2000, Celgene and Prudential Securities entered into a formal
engagement letter regarding the financial terms under which Prudential
Securities would serve as Celgene's exclusive financial advisor with respect to
the proposed acquisition of Signal.

On June 7, 2000, John P. Walker, Signal's chairman of the board, Drs. Lewis and
Anderson and Mr. Gordon visited Celgene's facility in Warren, New Jersey, and
met with Mr. Jackson, Dr. Barer and Mr. Hugin, to continue discussions regarding
the proposed merger. At the meeting, the parties discussed general business and
financial terms of the proposed merger.

On June 9, 2000, Dr. Lewis and Mr. Gordon met at Cooley Godward's offices in San
Diego with  representatives  of Cooley  Godward and Ernst & Young LLP,  Signal's
independent auditors, to discuss potential legal and accounting issues regarding
the proposed  merger.  Also on June 9, 2000,  Signal's board of directors held a
telephonic  special meeting to discuss the status of negotiations  regarding the
proposed merger and potential financial terms of the transaction.

On June 13, 2000, representatives of Robertson Stephens visited Celgene's
facility in Warren, New Jersey, to conduct further due diligence review of
Celgene on behalf of Signal and to discuss with Celgene the proposed structure
of the transaction, including proposed financial terms.

On June 15, 2000, Mr. Walker and Mr. Jackson had a telephone conversation to
discuss the financial terms of the proposed transaction.


                                       39
<PAGE>

On June 16, 2000, Signal's board of directors held a telephonic special meeting
to discuss the status of negotiations regarding the proposed merger and
potential financial terms of the transaction.

On June 16, 2000, Dr. Barer, Joseph J. Day, Celgene's senior vice president,
planning and business development, Pennie & Edmonds, LLP, outside patent counsel
to Celgene, and Prudential Securities, met at the offices of Proskauer Rose LLP,
to discuss intellectual property and contractual due diligence.

On June 19, 2000, Proskauer Rose LLP, circulated a first draft of the proposed
merger agreement to Signal, Celgene and their respective representatives and
advisors. At this time, Proskauer Rose also circulated a first draft of a letter
of intent between the parties regarding the proposed merger, including a binding
obligation of Signal to pay a break-up fee to Celgene under specified
circumstances.

On June 20, 2000, Celgene's board of directors held a special meeting to review
the terms of the transaction with Signal and approved the concept of the
transaction at this meeting, representatives of Prudential Securities presented
a number of analyses to the Celgene board regarding the transaction.

On June 21 and 22, 2000, representatives of Celgene and Signal and their
respective financial and legal advisors met at the offices of Proskauer Rose in
New York City to negotiate the terms of the letter of intent and the merger
agreement.

On June 21, 2000, Dr. Lewis and Dr. Barer had lunch in New York and discussed
the potential role of Signal senior executives in a post-merger organization.

On June 22, 2000, Signal's board of directors held a telephonic special meeting
to receive a status report on Signal's due diligence investigations of Celgene
and the results of the continuing merger discussions with Celgene.
Representatives of Robertson Stephens and Cooley Godward participated in the
meeting. At the meeting, Signal's board considered the terms of the proposed
transaction with Celgene, including the terms of the proposed letter of intent
and merger agreement, as well as the terms of a proposed stock option to be
granted to Celgene to purchase shares of Signal common stock and arrangements
obligating officers, directors and principal shareholders of Signal to vote in
favor of the proposed merger. Signal's board also considered the preliminary
analyses of Robertson Stephens regarding the proposed merger from a financial
point of view, as well as alternatives to effecting the merger, including
possible financing alternatives. Based upon its review of the information
presented at the meeting, Signal's board authorized Signal's officers to enter
into the proposed letter of intent with Celgene and authorized Signal's
representatives to continue to negotiate the terms of the merger agreement and
related documents.

On June 22, 2000, Celgene and Signal entered into a letter of intent regarding
the terms of the proposed merger, including a binding obligation of Signal to
pay a break-up fee of $10,000,000 to Celgene under specified circumstances.

Between June 22, 2000 and June 28, 2000, representatives of Celgene and Signal
and their respective financial and legal advisors conducted negotiations
regarding the terms of the definitive merger agreement, option agreement, proxy
and voting agreements and related documents. During this time, the directors of
Signal received from Signal management reports on the status of the merger
negotiations and draft copies of the merger agreement and related documents.

On June 23, 2000, Dr. Barer, Mr. Hugin and representatives of Prudential
Securities visited Signal's offices in San Diego, California, to review Signal
programs and personnel evaluations, and to conduct further due diligence on
Signal.

On June 27, 2000, the compensation committee of Celgene's board of directors
held a telephonic meeting to review compensation issues relating to the proposed
transaction between Celgene and Signal. In addition, by a special telephonic
meeting, Celgene's board of directors delegated approval authority for the
merger to its executive committee.

On June 27, 2000, Dr. Lewis and Dr. Barer held a conference call to review the
conditions of approval of the transaction between Celgene and Signal by
Celgene's board of directors.

On June 28, 2000, Mr. Jackson, Dr. Barer, Dr. Lewis and Mr. Gordon held a
conference call to identify and review current open issues regarding the
transaction. In addition, on June 28, 2000, the Executive Committee of Celgene's
board of directors held a telephonic meeting whereby authority to sign a merger
agreement with Signal on behalf of Celgene was delegated to Mr. Jackson.


                                       40
<PAGE>

Another telephonic special meeting of Signal's board of directors was held on
June 28, 2000 to consider the terms of the merger agreement, the option
agreement, the proxy and voting agreements and the transactions contemplated
thereby. Representatives of Robertson Stephens and Cooley Godward participated
in the meeting. Prior to the meeting, Signal's directors had been provided with
near-final versions of the merger agreement and related documents, as well as a
draft of a fairness opinion from Robertson Stephens and financial analysis
underlying the opinion. At the meeting, Signal's board received a report from
Cooley Godward and Mr. Walker summarizing the terms of the merger agreement and
related arrangements. Specifically, the Cooley Godward representatives discussed
the material terms of the proposed merger, including the structure of the
merger, the tax and accounting treatment for the merger, the exchange ratio,
termination provisions and associated break-up fees and proposed employment
arrangements between Celgene and key employees of Signal. Signal's board also
received a presentation from Robertson Stephens regarding the financial terms of
the proposed merger and the analysis undertaken by Robertson Stephens in
connection with its opinion. Robertson Stephens then delivered to Signal's board
its opinion that the exchange ratio was fair, from a financial point of view, to
the shareholders of Signal.

     Following the presentations by Robertson Stephens and Cooley Godward,
Signal's board reviewed the fairness opinion and other information presented by
Robertson Stephens and the terms of the merger, the merger agreement and the
related documents, and discussed the potential advantages and disadvantages of
and risks associated with the merger. After discussion, Signal's board
unanimously determined that the terms of the merger agreement and related
transactions were fair to, and in the best interests of, Signal and its
shareholders. Accordingly, Signal's board unanimously approved the merger, the
merger agreement, the option agreement, the proxy and voting agreements and all
related transactions and resolved to recommend that:

o  the Signal shareholders vote in favor of approval of the principal terms of
   the merger and adoption and approval of the merger; and

o  the holders of Signal preferred stock vote in favor of approval of the
   conversion of all outstanding shares of Signal preferred stock, effective
   immediately prior to the effective time of the merger.

On June 29, 2000, numerous conference calls took place between key executives of
Celgene and Signal to work out the final details of the merger and the merger
agreement and other related agreements.

Following the approval of the Celgene board and the Signal board, the merger
agreement and related documents in their definitive forms were executed and
delivered by the parties on June 29, 2000. On June 30, 2000, Celgene and Signal
issued a joint press release publicly announcing the merger.


RECOMMENDATION OF SIGNAL'S BOARD OF DIRECTORS

Signal's board of directors has determined that the merger is advisable and in
the best interests of Signal and its shareholders and has unanimously
recommended a vote for:

o  approval of the principal terms of the merger;

o  approval and adoption of the merger; and

o  conversion of the outstanding shares of Signal preferred stock into Signal
   common stock, effective immediately prior to the effective time of the
   merger.


SIGNAL'S REASONS FOR THE MERGER

Signal's board of directors reviewed a wide variety of information and
considered a number of factors in connection with its evaluation of the merger
and the merger agreement, and determined that the proposed merger provides an
opportunity that serves the best interests of Signal and its shareholders. In
particular, Signal's board of directors considered, among other things:

o  the likelihood that by providing Signal with greater financial security and
   leverage, the merger may benefit Signal when negotiating with potential
   collaboration partners or other licensees, enabling Signal to achieve
   improved financial terms and conditions;


                                       41
<PAGE>

o  the existence of a public market for the Celgene common stock to be received
   by Signal's shareholders in the merger, in contrast to the illiquid nature of
   their present private holdings of Signal capital stock;

o  the time and likelihood for realizing superior benefits through alternative
   business strategies, including an initial public offering of Signal's common
   stock;

o  information concerning Signal's and Celgene's respective business models,
   plans and operations, historical and projected financial performance and
   future business prospects;

o  the strategic fit between Signal and Celgene, including the benefits that
   could be derived from combining Signal's proprietary discovery technologies
   and programs with Celgene's development and commercialization capabilities
   and programs, in particular:

   o Celgene's expertise in clinical and regulatory matters regarding the
     development and commercialization of pharmaceutical products;

   o Celgene's experience in developing and commercializing pharmaceutical
     products, which may improve Signal's ability to retain control and
     ownership of product development programs until later stages, or permit
     Signal to participate in the commercialization of any products it may
     develop and thus retain a greater percentage of revenues and profits from
     product sales; and

   o the complementary nature of Signal's and Celgene's strategic focus,
     scientific and medical expertise and drug development programs in the
     fields of cancer and inflammatory diseases;

o  the financial consideration to be received by Signal's shareholders;

o  the ability to retain significant upside potential, with potentially reduced
   downside risk, through continued ownership of stock in a combined entity;

o  the compatibility of the management and business of Signal with those of
   Celgene;

o  a presentation by Robertson Stephens regarding the merger, including its
   fairness opinion;

o  the opportunity for Signal's shareholders to receive Celgene common stock in
   a "reorganization" within the meaning of Section 368(a) of the Code and thus
   continue to participate in the growth of the business conducted by the
   combined company after the merger without paying current United States
   federal income tax (except to the extent that such shareholders receive cash
   in lieu of fractional shares);

o  the effect of the merger on Signal's employees and collaboration partners;
   and

o  the terms and conditions of the merger, including:

   o the nature of the option agreement and voting and proxy agreements to be
     executed by Signal's officers and directors and some of Signal's
     shareholders;

   o the limitations on Signal's ability to consider alternative acquisition
     proposals from third parties following execution of the merger agreement;
     and

   o the size of the break-up termination fees and the events that would result
     in the payment of those fees.

Signal's board of directors also considered a variety of potentially negative
factors in its deliberations concerning the merger. In particular, Signal's
board considered, among other things:

o  the potential disruption of Signal's business that might result from employee
   uncertainty and lack of focus following announcement of the merger and in
   connection with integrating the operations of Signal and Celgene;

o  the possibility that the merger might not be consummated;

o  the risk of withdrawing Signal's registration statement on Form S-1 and
   discontinuing its proposed initial public offering;


                                       42
<PAGE>

o  the risk of disrupting relationships with current and prospective
   collaboration partners, academic collaborators and key service providers;

o  the effects of the public announcement of the merger on Signal's ability to
   secure additional working capital financing on terms acceptable to Signal,
   its ability to attract and retain key management and technical personnel and
   the progress of certain of its development projects;

o  the risk that the market price of Celgene common stock might decline in
   response to the public announcement of the merger;

o  the risks associated with potential volatility in the market price of Celgene
   common stock;

o  the risk that the other benefits sought to be achieved by the merger will not
   be achieved; and

o  other risks described above under "Risk Factors."

After taking into consideration all of the factors set forth above, Signal's
board of directors determined that the merger was in the best interests of
Signal and its shareholders and that Signal should proceed with the merger at
this time.

Signal does not intend the foregoing discussion of the information and factors
considered and given weight by Signal's board of directors to be exhaustive. In
view of the variety of factors that Signal's board of directors considered in
connection with its evaluation of the merger, Signal's board did not find it
practicable to, and did not, quantify or otherwise assign relative weights to
the specific factors that it considered in reaching its determination. In
addition, individual members of Signal's board may have given different weights
to different factors. For a discussion of the interests of some members of
Signal's management and Signal's board relating to the merger, you should read
"The Merger-- Related Agreements and Interests of Certain Persons in the
Merger."


CELGENE'S REASONS FOR THE MERGER

Celgene's primary reasons for seeking to consummate a business combination with
Signal are the beliefs of Celgene's board of directors and management that a
business combination would result in a number of benefits for Celgene and its
stockholders, including the belief that:

o  The combination of Celgene's capabilities in drug development and
   commercialization and Signal's research capabilities in gene regulation and
   signal transduction technologies will position Celgene to capitalize on
   anticipated developments in drug discovery based on advances in genomics and
   proteomics.

o  Signal's strengths are focused in the areas of intracellular signaling based
   on gene and protein regulation. Celgene believes that future development of
   new drugs will rely in important ways on the discovery of pharmaceuticals
   designed to modulate targets within the cell and that regulate disease
   associated genes and proteins.

o  Signal's scientists, intellectual property, compound libraries and target
   screens and emerging clinical candidates complements Celgene's existing
   capabilities and provides added resources and expertise to further accelerate
   the development of Celgene's IMiDs and SelCIDs programs.


                                       43
<PAGE>

              OPINION AND ANALYSIS OF SIGNAL'S FINANCIAL ADVISOR

Signal engaged Robertson Stephens to render an opinion as to the fairness of the
exchange ratio in the proposed merger, from a financial point of view, to the
"holders of Signal common stock." (See Appendix C for a copy of the full
opinion.) The "holders of Signal common stock" was defined in Robertson
Stephens' written opinion letter to the board of directors of Signal, dated June
28, 2000, as all holders of Signal common stock (including holders of Signal
preferred stock which is to be converted into Signal common stock immediately
prior to the merger) other than Celgene, Celgene Acquisition Corp., any
affiliates of Celgene or Celgene Acquisition Corp. or holders of dissenting
shares; provided, that with respect to any holders of Signal common stock who
are officers or directors (or who have representatives serving as directors) of
Signal, Robertson Stephens expressed its opinion as to such holders solely in
their capacity as holders of Signal common stock and did not taken into account
any other agreements or arrangements that they may have in connection with the
merger.

On June 28, 2000, at a meeting of Signal's board held to evaluate the proposed
merger, Robertson Stephens delivered its written opinion to Signal's board that,
as of June 28, 2000 and based on the matters considered and the limitations on
the review undertaken described in the opinion, the exchange ratio in the
proposed merger was fair from a financial point of view to the holders of Signal
common stock. The exchange ratio was determined through negotiations between the
respective managements of Signal and Celgene. Robertson Stephens was not asked
by, and did not recommend to, Signal that any specific exchange ratio
constituted the appropriate exchange ratio for the merger.

You should consider the following when reading the discussion of the opinion of
Signal's financial advisor in this document:

   o We urge you to read carefully the entire opinion of Robertson Stephens,
     which is set forth in Appendix C to this proxy statement/prospectus and is
     incorporated by reference. The following description of the Robertson
     Stephens opinion is qualified by reference to the full opinion located in
     Appendix C. The full opinion sets forth, among other things, the
     assumptions made by Robertson Stephens, the matters it considered and the
     limitations on the review undertaken.

   o The Robertson Stephens opinion was prepared for the information of Signal's
     board in connection with its evaluation of the merger and does not
     constitute a recommendation to the shareholders of Signal or Celgene as to
     how they should vote, or take any other action, with respect to the merger.

   o The Robertson Stephens opinion did not address the relative merits of the
     merger and the other business strategies that Signal's board has
     considered, nor does it address the decision of Signal's board to proceed
     with the merger.

   o The Robertson Stephens opinion was necessarily based upon market, economic
     and other conditions that were in effect on, and information made available
     to Robertson Stephens as of, the date of the opinion. You should understand
     that subsequent developments may affect the conclusion expressed in the
     Robertson Stephens opinion, and that Robertson Stephens disclaims any
     undertaking or obligation to advise any person of any change in any matter
     affecting its opinion which may come or be brought to Robertson Stephens
     attention after the date of its opinion.

   o The Robertson Stephens opinion was limited to the fairness, from a
     financial point of view and as of the date thereof, of the exchange ratio
     in the merger to the holders of Signal common stock.

   o In connection with the preparation of its opinion, Robertson Stephens was
     not authorized to solicit, and did not solicit, third parties regarding
     alternatives to the merger.


OPINION AND ANALYSIS OF ROBERTSON STEPHENS

In connection with the preparation of the Robertson Stephens opinion, Robertson
Stephens:

   o reviewed certain publicly available financial statements and other business
     and financial information of Signal and Celgene, respectively;


                                       44
<PAGE>

   o reviewed certain internal financial statements and other financial and
     operating data, including certain financial forecasts and other
     forward-looking information, concerning Signal prepared by the management
     of Signal;

   o reviewed certain publicly available estimates of research analysts relating
     to Celgene;

   o held discussions with the respective managements of Signal and Celgene
     concerning the businesses, past and current operations, financial condition
     and future prospects of both Signal and Celgene, independently and
     combined, including discussions with the managements of Signal and Celgene
     concerning cost savings and other synergies that were expected to result
     from the merger as well as their views regarding the strategic rationale
     for the merger;

   o reviewed the financial terms and conditions set forth in drafts, dated June
     26, 2000, of the merger agreement, the voting and proxy agreements and the
     option agreement;

   o reviewed the stock price and trading history of Celgene common stock;

   o compared the financial performance of Celgene and the prices and trading
     activity of Celgene common stock with that of certain other publicly traded
     companies comparable to Celgene;

   o compared the financial performance of Signal with that of certain publicly
     traded companies comparable to Signal;

   o compared the financial terms of the merger with the financial terms, to the
     extent publicly available, of other transactions that Robertson Stephens
     deemed relevant;

   o reviewed the pro forma impact of the merger;

   o participated in discussions and negotiations among representatives of
     Signal and Celgene and their financial and legal advisors; and

   o made such other studies and inquiries, and reviewed such other data, as it
     deemed relevant.

In its review and analysis, and in arriving at its opinion, Robertson Stephens
assumed and relied upon the accuracy and completeness of all of the financial
and other information provided to Robertson Stephens (including information
furnished to it orally or otherwise discussed with it by the managements of
Signal and Celgene) or publicly available and neither attempted to verify, nor
assumed responsibility for verifying, any of such information. Robertson
Stephens relied upon the assurances of the managements of Signal and Celgene
that they were not aware of any facts that would make such information
inaccurate or misleading. Furthermore, Robertson Stephens did not obtain or
make, or assume any responsibility for obtaining or making, any independent
evaluation or appraisal of the properties, assets or liabilities (contingent or
otherwise) of Signal or Celgene, nor was it furnished with any such evaluation
or appraisal.

With respect to the financial forecasts and other forward-looking financial
information (and the assumptions and bases therefor) for each of Signal and
Celgene that Robertson Stephens reviewed, Robertson Stephens has assumed that:

   o these forecasts and other forward-looking financial information were
     reasonably prepared in good faith on the basis of reasonable assumptions;

   o these forecasts and other forward-looking financial information reflected
     the best currently available estimates and judgments as to the future
     financial condition and performance of each of Signal and Celgene; and

   o these forecasts and other forward-looking financial information would be
     realized in the amounts and in the time periods currently estimated.

In addition, Robertson Stephens assumed that:

   o the merger will be consummated upon the terms set forth in the drafts,
     dated June 26, 2000, of the merger agreement, the voting and proxy
     agreements and the option agreement without material alteration thereof,
     including, among other things, that the merger will be accounted for as a
     "pooling-of-interests" business combination in accordance with U.S.
     generally accepted accounting principles;


                                       45
<PAGE>

   o the merger will be treated as a tax-free reorganization pursuant to the
     Internal Revenue Code of 1986, as amended; and

   o the historical financial statements of each of Signal and Celgene reviewed
     by Robertson Stephens were prepared and fairly presented in accordance with
     U.S. generally accepted accounting principles consistently applied.

   Robertson Stephens expressed no opinion as to:

   o the value of any employee agreement or other arrangement entered into in
     connection with the merger;

   o any tax or other consequences that may result from the merger; or

   o what the value of the Celgene common stock will be when issued to
     Signal's shareholders pursuant to the merger or the price at which the
     shares of Celgene's common stock that are issued pursuant to the merger
     may be traded in the future.

The following is a summary of the material financial analyses performed by
Robertson Stephens in connection with rendering its opinion. The summary of the
financial analyses is not a complete description of all of the analyses
performed by Robertson Stephens. Certain of the information in this section is
presented in tabular form. IN ORDER TO UNDERSTAND THE FINANCIAL ANALYSES
PERFORMED BY ROBERTSON STEPHENS, THESE TABLES MUST BE READ TOGETHER WITH THE
TEXT ACCOMPANYING EACH TABLE.


SIGNAL COMPARABLE COMPANY ANALYSIS

Using publicly available information, Robertson Stephens analyzed, among other
things, the total capitalization and trading multiples of the following selected
publicly traded companies in the pharmaceutical and biotechnology industry which
Robertson Stephens believed to be reasonably comparable to Signal:

     o Ariad Pharmaceuticals, Inc.

     o AXYS Pharmaceuticals, Inc.

     o Isis Pharmaceuticals, Inc.

     o Microcide Pharmaceuticals, Inc.

     o Sangamo BioSciences, Inc.

     o Synaptic Pharmaceutical Corporation

     o Tularik Inc.

Total capitalization means the market capitalization of the company's equity
plus debt outstanding less balance sheet cash. As set forth in the following
table, applying a range of multiples for the selected publicly traded companies
of estimated calendar year 2000 revenues and projected calendar year 2001 and
2002 revenues to corresponding revenue data for Signal resulted in the following
ranges of multiples of total capitalization, implied equity values, prices per
share and exchange ratios:

<TABLE>
<CAPTION>
                                                 IMPLIED EQUITY VALUES                                  IMPLIED
CALENDAR YEAR                   MULTIPLE RANGE       (IN MILLIONS)       IMPLIED PRICE PER SHARE     EXCHANGE RATIO
------------------------------ ---------------- ----------------------- ------------------------- -------------------
<S>                            <C>              <C>                     <C>                       <C>
2000 (estimated)                21.0x - 50.6x      $238.3 - $566.0           $7.32 - $17.40       0.1263 - 0.2999
2001 (projected)                24.5x - 57.0x      $221.5 - $507.9           $6.81 - $15.61       0.1174 - 0.2692
2002 (projected)                22.1x - 72.3x      $126.5 - $402.4           $3.89 - $12.37       0.0670 - 0.2133
MEAN                                                                         $6.01 - $15.13       0.1036 - 0.2608
EXCHANGE RATIO IN THE MERGER                                                                            0.1257
</TABLE>

The implied equity values reflected Signal's net debt of $4.8 million as of
March 22, 2000. The implied share prices were based on 32,534,000 diluted Signal
shares outstanding using the treasury stock method for options and warrants. The
implied exchange ratios were based on a share price of $58.00 for Celgene common
stock. Revenue data for the selected publicly traded companies were obtained
from research analysts estimates and company reports.


                                       46
<PAGE>

PRECEDENT TRANSACTION ANALYSIS

Using publicly available information, Robertson Stephens analyzed the
consideration offered and the premiums paid in the following selected
acquisition transactions in the biotechnology industry (listing the targets
followed by the acquiror and with the date these transactions were publicly
announced in parenthesis) which Robertson Stephens believed to be reasonably
comparable to the merger:

     o LeukoSite, Inc./Millennium Pharmaceuticals, Inc. (October 14, 1999)

     o Allelix Biopharmaceuticals, Inc./NPS Pharmaceuticals, Inc. (September 27,
       1999)

     o SUGEN, Inc./Pharmacia & Upjohn, Inc. (June 15, 1999)

     o GeneMedicine, Inc./Megabios Corp. (October 26, 1998)

In analyzing these "precedent transactions," Robertson Stephens compared, among
other things, the total consideration in such transactions as a multiple of the
next twelve months, or "NTM", estimated revenues of the target prior to the
announcement of the transaction. All multiples for the precedent transactions
were based on public information available at the time of the announcement.
Based on this information and other publicly available information, the
following table illustrates the implied equity values, prices per share and
exchange ratios derived from applying a range of multiples of total
consideration that Robertson Stephens derived from these transactions to
corresponding revenue data for Signal:

<TABLE>
<CAPTION>
                                                     IMPLIED EQUITY
                                                         VALUES          IMPLIED PRICE          IMPLIED
                                  MULTIPLE RANGE      (IN MILLIONS)        PER SHARE         EXCHANGE RATIO
                                 ----------------   ----------------   ----------------   -------------------
<S>                              <C>                <C>                <C>                <C>
NTM Revenue                      5.8x - 29.5x       $77.9 - $380.0     $2.40 - $11.68     0.0413 - 0.2014
 EXCHANGE RATIO IN THE MERGER                                                                   0.1257
</TABLE>

FINANCING HISTORY ANALYSIS

Robertson Stephens reviewed the financing history of Signal. This review showed
a post-money equity valuation of Signal of $112.0 million, based on a private
placement of preferred stock on October 1, 1999, Signal's most recent financing
transaction. The latest post-money equity valuation resulted in an implied price
per share of Signal common stock of $3.44 and an implied exchange ratio of
0.0594, as compared to an exchange ratio of 0.1257 in the merger.


IPO FILING ANALYSIS

Robertson Stephens reviewed the Form S-1 filed by Signal on March 22, 2000, in
connection with its proposed initial public offering. This review showed implied
equity values ranging from $205.5 million to $237.0 million, implied prices per
share of Signal common stock ranging from $6.32 to $7.28 and implied exchange
ratios ranging from 0.1089 to 0.1256, as compared to an exchange ratio of 0.1257
in the merger.


CELGENE COMPARABLE COMPANY ANALYSIS

Using publicly available information, Robertson Stephens analyzed, among other
things, the total capitalization and trading multiples of the following selected
publicly traded companies in the pharmaceutical and biotechnology industry which
Robertson Stephens believed to be reasonably comparable to Celegene:

     o Cephalon, Inc.

     o COR Therapeutics, Inc.

     o SuperGen, Inc.

     o Vertex Pharmaceuticals Incorporated

In examining these selected publicly traded companies, Robertson Stephens
calculated the total capitalization of each company as a multiple of its
respective estimated calendar year 2000 revenues and projected calendar year
2001 and 2002 revenues and compared such multiples to the


                                       47
<PAGE>

corresponding multiples for Celgene. Revenue data for the selected publicly
traded companies were obtained from research analysts estimates and company
reports. Robertson Stephens' analysis of these selected publicly traded
companies resulted in the following multiples of total capitalization:

<TABLE>
<CAPTION>
             CY 2000 REVENUE     CY 2001 REVENUE     CY 2002 REVENUE
               (ESTIMATED)         (PROJECTED)         (PROJECTED)
            -----------------   -----------------   ----------------
<S>         <C>                 <C>                 <C>
Mean               78.3x               25.0x               19.9x
Median             43.6x               17.2x               13.7x
Celgene            58.0x               34.0x               22.1x
</TABLE>

Based on an analysis of this data, Robertson Stephens concluded that the trading
multiples of Celgene common stock were within the range of the comparable
companies.


OTHER FACTORS

No company, business or transaction compared in the comparable companies
analysis or precedent transaction analysis is identical to Signal or the
proposed merger. Accordingly, an analysis of the results of the foregoing is not
entirely mathematical; rather it involves complex considerations and judgments
concerning differences in financial and operating characteristics and other
factors that could affect the public trading, acquisition and other values of
the comparable companies, precedent transactions or the business segment,
company or transaction to which they are being compared.

While this summary describes the analysis and factors that Robertson Stephens
deemed material in its presentation to the Signal board, it is not a
comprehensive description of all analysis and factors considered by Robertson
Stephens. The preparation of a fairness opinion is a complex process that
involves various determinations as to the most appropriate and relevant methods
of financial analysis and the application of these methods to the particular
circumstances. Therefore, a fairness opinion is not readily susceptible to
partial analysis or summary description. In arriving at its opinion, Robertson
Stephens did not attribute any particular weight to any analysis or factor
considered by it, but rather made qualitative judgments as to the significance
and relevance of each analysis and factor. Accordingly, Robertson Stephens
believes that its analyses must be considered as a whole and that selecting
portions of its analyses and of the factors considered by it, without
considering all analyses and factors, could create a misleading or incomplete
view of the evaluation process underlying its opinion. Several analytical
methodologies were employed and no one method of analysis should be regarded as
critical to the overall conclusion reached by Robertson Stephens. Each
analytical technique has inherent strengths and weaknesses, and the nature of
the available information may further affect the value of particular techniques.
The conclusion reached by Robertson Stephens is based on all analyses and
factors taken as a whole and also on application of Robertson Stephens' own
experience and judgment. This conclusion may involve significant elements of
subjective judgment and qualitative analysis. Robertson Stephens expresses no
opinion as to the value or merit standing alone of any one or more parts of the
analysis it performed. In performing its analyses, Robertson Stephens made
numerous assumptions with respect to industry performance, general business and
other conditions and matters, many of which are beyond the control of Signal,
Celgene or Robertson Stephens. Any estimates contained in these analyses are not
necessarily indicative of actual values or predictive of future results or
values, which may be significantly more or less favorable than those suggested
by these analyses. Accordingly, analyses relating to the value of businesses do
not purport to be appraisals or to reflect the prices at which these businesses
actually may be sold in the future, and these estimates are inherently subject
to uncertainty.

The engagement letter between Robertson Stephens and Signal provides that, for
its services, Robertson Stephens is entitled to receive a transaction fee equal
to an amount calculated pursuant to a formula based upon the aggregate
transaction value, which fee was approximately $2.8 million as of the date of
the fairness opinion. Such transaction fee will be payable upon completion of
the merger. Robertson Stephens also received a fee of $200,000 upon the delivery
of the Robertson Stephens fairness opinion, which fee is in addition to the
transaction fee and was payable without regard to the conclusion reached in the
opinion. Signal has also agreed to reimburse Robertson Stephens for its
reasonable and customary out-of-pocket expenses related to this work, including
legal fees (subject to certain limitations), and to


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<PAGE>

indemnify and hold harmless Robertson Stephens and its affiliates and any other
person, director, employee or agent of Robertson Stephens or any of its
affiliates, or any person controlling Robertson Stephens or its affiliates, for
certain losses, claims, damages, expenses and liabilities relating to or arising
out of services provided by Robertson Stephens as financial advisor to Signal.
The terms of the fee arrangement with Robertson Stephens, which Signal and
Robertson Stephens believe are customary in transactions of this nature, were
negotiated at arm's length between Signal and Robertson Stephens, and the Signal
board was aware of these fee arrangements.

In the past, Robertson Stephens has provided certain investment banking services
to Signal, including acting as lead manager for Signal's filing of an initial
public offering, and Robertson Stephens and its affiliates are also shareholders
of Signal. In the ordinary course of its business, Robertson Stephens may
actively trade Celgene's securities for its own account and for the account of
its customers and, accordingly, may at any time hold a long or short position in
Celgene's securities.

Robertson Stephens is an internationally recognized investment banking firm and
was retained based on its experience as a financial advisor in connection with
mergers and acquisitions and in securities valuations generally. As part of its
investment banking business, Robertson Stephens is frequently engaged in the
valuation of businesses and their securities in connection with mergers and
acquisitions, negotiated underwritings, secondary distributions of securities,
private placements and other purposes.


MERGER CONSIDERATION

Upon consummation of the merger, each outstanding share of Signal common stock
(including shares of Signal preferred stock which will be converted into Signal
common stock immediately before the merger), other than shares owned by holders
who are exercising dissenters' rights under California law, will be converted
automatically into the right to receive 0.1257 of a share of Celgene common
stock, par value $.01 per share.


STOCK OPTIONS AND WARRANTS

Under the merger agreement, each option and warrant to purchase Signal common
stock or Series C-1 or Series C-2 preferred stock outstanding immediately prior
to the effective time of the merger, whether vested or unvested, will cease to
represent a right to acquire shares of Signal common stock or Series C-1 or
Series C-2 preferred stock and will be converted, at the effective time of the
merger, into an option or warrant to acquire, on the same terms and conditions,
the number of shares of Celgene common stock determined by multiplying the
number of shares of Signal common stock or Series C-1 or Series C-2 preferred
stock subject to that Signal stock option or warrant by 0.1257, rounded down, if
necessary, to the nearest whole share. The exercise price of these stock options
or warrants will be the exercise price for the stock option or warrant
immediately prior to the effective time of the merger divided by 0.1257, rounded
up to the nearest cent.

Celgene will file a registration statement on Form S-8 covering the issuances of
the shares of Celgene common stock subject to each Signal option or warrant.


DISSENTERS' RIGHTS

Under California law, holders of Signal capital stock who did not vote in favor
of the merger will be entitled to dissenters' rights as set forth in Sections
1300 through 1312 of the California General Corporation Law, a copy of which is
attached to this proxy statement as Appendix B.

A vote against the merger does not in itself constitute a demand for dissenters'
rights. In order to qualify for dissenters' rights, the shares in question must
satisfy each of the following requirements:

- the shares must have been outstanding on the date of determination of
  shareholders entitled to vote on the merger;

- the shares must not have been voted in favor of the merger;

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<PAGE>

- the holder of those shares must make a written demand that Signal repurchase
   his or her shares at fair market value; and

- the shareholder must submit certificates representing those shares for
  endorsement.


A Signal shareholder who properly follows the procedures for exercising
dissenters' rights for his or her stock may be entitled to receive in cash the
fair value of his or her stock instead of the consideration provided under the
terms of the merger agreement. The fair market value is the value of the shares
as of the day before the announcement of the merger.


Under California law, within ten days following the approval of the merger,
Signal is required to mail to all shareholders who did not vote in favor of the
merger a notice of the approval of the merger, a statement of the price
determined by Signal to represent the fair market value of the shares and a
description of the procedures for exercising dissenters' rights. The fair market
value set forth in the mailing is treated as an offer by Signal to purchase any
Signal shares at that price.

Signal shareholders who wish to exercise their dissenters' right must demand
that Signal repurchase their shares within thirty days after the date on which
the notice of approval of the merger was mailed. The demand must state the
number, class and fair market value of the shares. The fair market value set
forth in the demand is considered an offer by the dissenting shareholder to sell
his or her shares at that price within a thirty-day period. The shareholder must
also submit to Signal certificates for those shares to be repurchased. Unless
there is any dispute as to the fair market value or status of the shares, Signal
is required by law to pay the shareholder the fair market value for his or her
shares within thirty days of the date of agreement on the price of the shares or
within thirty days after any statutory or contractual conditions to the merger
are satisfied, whichever is later.

If Signal and the dissenting shareholder disagree as to the price of the shares
or disagree as to whether the shares qualify as dissenting, the shareholder may
bring an action in California Superior Court to resolve the dispute within six
months after the date on which the notice of the approval of the merger is
mailed.


EFFECTIVE TIME

The merger will become effective upon the filing of an agreement of merger with
the Secretary of State of the State of California, or such other time as the
parties may specify. This filing is anticipated to be made within two business
days after receipt of Signal shareholder approval and all required regulatory
approvals and the satisfaction or waiver of the other conditions to the merger.
See "The Merger Agreement and Related Agreements -- Conditions to the Merger."


CONVERSION  OF  SHARES;  PROCEDURES  FOR EXCHANGE OF CERTIFICATES; NO FRACTIONAL
SHARES

As promptly as practicable after the effective date of the merger, Celgene will
cause to be sent to each shareholder of record of Signal as of the effective
time of the merger transmittal materials for use in exchanging certificates of
Signal common stock (including shares of Signal preferred stock which will be
converted into Signal common stock immediately before the merger) for
certificates of Celgene common stock. The transmittal materials will contain
information and instructions on how to surrender Signal capital stock
certificates for new certificates representing Celgene common stock.

No fractional shares of Celgene common stock will be issued to holders of Signal
common stock in the merger; instead, Signal shareholders will receive cash in
lieu of the fraction of a share of Celgene common stock they would have
otherwise received following the effective time of the merger.

Until a holder of Signal common stock surrenders his, her or its certificates
representing shares of Signal capital stock, the certificates will, after the
effective time of the merger, represent for all purposes only the right to
receive Celgene common stock as specified in the merger agreement.


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<PAGE>

SIGNAL SHAREHOLDERS SHOULD NOT SURRENDER THEIR STOCK CERTIFICATES FOR EXCHANGE
UNTIL THEY RECEIVE A TRANSMITTAL FORM.


NASDAQ LISTING

Celgene will use its commercially reasonable efforts to cause the shares of
Celgene common stock to be issued in connection with the merger to be approved
for quotation on the Nasdaq National Market or listed on such securities
exchange as Celgene common stock is then listed, subject to official notice of
issuance.


EXPENSES

Except for the costs of this proxy statement/prospectus, which will be paid by
Celgene, all costs and expenses incurred in connection with the merger agreement
and the transactions contemplated in the merger agreement will be paid by the
party incurring such costs or expenses.


INTERESTS OF CERTAIN PERSONS IN THE MERGER

As of the record date, Signal directors and executive officers and their
affiliates owned approximately 6,853,825 shares of Signal capital stock, which
represented approximately 23% of the outstanding shares of Signal capital stock
entitled to vote at the Signal special meeting. Pursuant to the merger
agreement, Signal's directors and executive officers will receive the same
consideration for their shares of Signal common stock as the other Signal
shareholders.


  Employment Agreement

As part of the merger, Alan J. Lewis, president and chief executive officer of
Signal, is negotiating an employment agreement with Celgene to be effective upon
the consummation of the merger.


MATERIAL FEDERAL INCOME TAX CONSEQUENCES

The following summarizes the material United States federal income tax
consequences of the merger to holders of Signal capital stock who exchange their
stock for Celgene common stock in the merger. This summary is for general
information purposes only and does not consider all aspects of federal income
taxation that may be relevant to you because of your particular circumstances.

This discussion is generally limited to the United States federal income tax
consequences to Signal shareholders who will hold their shares of Signal capital
stock as capital assets within the meaning of Section 1221 of the Internal
Revenue Code of 1986, as amended, and will hold their shares of Celgene common
stock received in exchange therefor as capital assets.

This summary does not deal with the United States federal income tax
consequences to persons subject to special treatment under the Internal Revenue
Code such as:

o banks, thrifts and other financial institutions;

o mutual funds;

o real estate investment trusts;

o regulated investment companies;

o insurance companies;

o dealers in securities or currencies;

o tax-exempt investors;

o foreign shareholders;

o  persons that will hold Celgene common stock as a position in a "straddle," or
   as part of a "synthetic security" or "hedge," "conversion transaction" or
   other integrated investment;


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<PAGE>
o  persons who acquired  the  Signal  capital stock pursuant to the exercise of
   employee stock options or otherwise as compensation;

o  persons whose shares of Signal capital stock are qualified small business
   stock as defined by Section 1202 of the Internal Revenue Code;

o  persons that have a "functional currency" other than the U.S. Dollar; and

o  investors in pass-through entities, such as partnerships.

Further, it does not include any description of any alternative minimum tax
consequences or the consequences arising under United States federal gift and
estate taxes or the tax laws of any state, local or foreign government that may
be applicable to a holder of Celgene common stock.

Additionally the following discussion does not address:

o  the tax consequences of transactions effectuated before, after or at the same
   time as the merger, whether or not they are in connection with the merger,
   including, without limitation, transactions in which Signal shares are
   acquired or Celgene shares are disposed of;

o  the tax consequences to holders of options issued by Signal which are
   assumed, exercised or converted, as the case may be, in connection with the
   merger; or

o  the tax consequences of the receipt of Celgene shares other than in exchange
   for Signal shares.

This summary is based on the Internal Revenue Code, final and proposed Treasury
regulations thereunder and administrative and judicial interpretations thereof,
as of today. All of these are subject to change, possibly with retroactive
effect. Any change could alter the tax consequences to Celgene, Signal or the
Signal shareholders as described in this summary. Moreover, no rulings have been
or will be requested from the Internal Revenue Service with respect to any of
the matters addressed in this discussion.

You are advised to consult your tax advisor as to the United States federal
income tax consequences of the merger for your particular circumstances, as well
as the effect of any state, local, foreign or other tax laws and of potential
changes in applicable tax laws.

It is a condition to the obligation of the companies to consummate the merger
that each company receive an opinion at closing from its counsel, substantially
to the effect that the merger will be treated as a reorganization within the
meaning of Section 368(a) of the Internal Revenue Code. You should be aware that
these tax opinions do not bind the Internal Revenue Service. The Internal
Revenue Service could reach a different conclusion and a contrary position could
be sustained by a court. The tax opinions discussed in this section assume and
are conditioned upon the following:

o  that all representations, warranties and statements made or agreed to by
   Celgene, Celgene Acquisition Corp. and Signal, their managements, employees,
   officers, directors and shareholders in connection with the merger,
   including, but not limited to, those set forth in the merger agreement
   (including the exhibits thereto) and the tax representation letters delivered
   to such counsel by Celgene, Celgene Acquisition Corp. and Signal are true and
   accurate at all relevant times;

o  that original documents submitted to such counsel (including signatures
   thereto) are authentic, documents submitted to such counsel as copies conform
   to the original documents, and that all of these documents have been (or will
   be by the effective time) duly and validly executed and delivered where due
   execution and delivery are a prerequisite to the effectiveness of these
   documents;

o  that all covenants contained in the merger agreement (including exhibits
   thereto) and the tax representation letters, described above, are performed
   without waiver or breach of any material provision of these covenants;
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<PAGE>

o  that the merger will be reported by Celgene and Signal on their respective
   U.S. federal income tax returns in a manner consistent with the opinions
   rendered by such counsel; and

o  that any representation or statement made "to the knowledge of" or similarly
   qualified is correct without that qualification.

EXCHANGE OF SIGNAL CAPITAL STOCK INTO CELGENE COMMON STOCK

Subject to the assumptions and limitations discussed above, in the opinion of
Proskauer Rose LLP, tax counsel to Celgene, and Cooley Godward LLP, tax counsel
to Signal:

o  the merger will be treated for federal income tax purposes as a
   reorganization within the meaning of Section 368(a) of the Internal Revenue
   Code;

o  no gain or loss will be recognized by Signal, Celgene or Celgene Acquisition
   Corp. as a result of the merger;

o  you will not recognize income, gain or loss upon the exchange of your Signal
   capital stock for Celgene common stock in the merger, except to the extent of
   cash, if any, received in payment for a fractional share of Celgene common
   stock;

o  your aggregate tax basis in the Celgene common stock received (including a
   fractional share for which cash is received) should generally be equal to
   your tax basis in the Signal capital stock exchanged;

o  your holding period in Celgene common stock received should generally begin
   on the date you acquired the Signal capital stock exchanged; and

o  cash, if any received for a fractional share of Celgene common stock will be
   treated as if you received the fractional share pursuant to the merger and
   then sold such fractional share for cash. The amount of any gain or loss will
   be equal to the difference between the ratable portion of your tax basis in
   the Signal capital stock exchanged in the merger that is allocated to the
   fractional share and the cash received for it. Any gain or loss will
   constitute long-term capital gain or loss if your Signal capital stock has
   been held for more than one year at the time of consummation of the merger.


Even if the merger qualifies as a reorganization, you would recognize income
upon receipt of Celgene common stock to the extent that, for example, any such
shares were determined to have been received in exchange for services, to
satisfy obligations or in consideration for anything other than the Signal
common stock surrendered. Generally, such income is taxable as ordinary income
upon receipt. In addition, to the extent that you were treated as receiving,
directly or indirectly, consideration other than Celgene common stock in
exchange for your Signal capital stock, gain or loss would have to be
recognized.


BACKUP WITHHOLDING

With respect to a cash payment received by a Signal shareholder in lieu of a
fractional share of Celgene common stock, a noncorporate shareholder of Signal
may be subject to backup withholding at a rate of 31%. However, backup
withholding will not apply to a shareholder who either (i) furnishes a correct
taxpayer identification number and certifies that he or she is not subject to
backup withholding by completing the substitute Form W-9 that will be included
as part of the transmittal letter, or (ii) otherwise proves to Celgene and its
exchange agent that the shareholder is exempt from backup withholding.


INFORMATION REPORTING

Each Signal shareholder that receives Celgene common stock in the merger will be
required to file a statement with his or her federal income tax return setting
forth his or her basis in the Signal capital stock surrendered and the fair
market value of the Celgene common stock received in the merger, and to retain
permanent records of these facts relating to the merger.


                                       53
<PAGE>

A successful challenge by the IRS to the reorganization status of the merger
would result in significant adverse tax consequences to you. Signal shareholders
would recognize taxable gain or loss with respect to each share of Signal
capital stock surrendered equal to the difference between each shareholder's
basis in such share and the fair market value, as of the effective time of the
merger, of the Celgene common stock received in exchange therefor. In such
event, your aggregate basis in the Celgene common stock received would equal its
fair market value, and the holding period of such stock would begin the day
after the effective date of the merger.


ACCOUNTING TREATMENT

The merger is intended to qualify as a pooling-of-interests. The
pooling-of-interests method of accounting assumes the companies had always been
combined, and the historical financial statements for periods prior to closing
of the merger are restated as though the companies had always been combined as
required under United States generally accepted accounting principles. The
assets and liabilities of Celgene and Signal will be carried forward by the
combined company at their historical recorded amounts.


REGULATORY APPROVALS

Transactions such as the merger are subject to review by the Department of
Justice and the Federal Trade Commission to determine whether they comply with
applicable antitrust laws. Under the provisions of the Hart-Scott-Rodino Act,
the merger may not be consummated until the specified waiting period
requirements of the HSR Act have been satisfied. Celgene and Signal filed
notification reports, together with requests for early termination of the
waiting period, with the Department of Justice and the Federal Trade Commission
under the HSR Act on July 11, 2000, and the waiting period terminates on August
10, 2000 unless extended or terminated earlier.


RESALE OF CELGENE COMMON STOCK FOLLOWING THE MERGER

The shares of Celgene common stock to be issued in connection with the merger
will be registered under the Securities Act of 1933 and will be freely
transferable under the Securities Act, except for shares of Celgene common stock
issued to any person who is deemed to be an "affiliate" of Signal at the time of
the special meeting. Persons who may be deemed to be affiliates include
individuals or entities that control, are controlled by, or are under the common
control of Signal and may include executive officers and directors of Signal, as
well as significant shareholders of Signal. Affiliates may not sell their shares
of Celgene common stock acquired in connection with the merger except pursuant
to:

o  an effective registration statement under the Securities Act covering the
   resale of those shares;

o  an exemption under paragraph (d) of Rule 145 under the Securities Act; or

o  any other applicable exemption under the Securities Act.


Celgene's registration statement on Form S-4, of which this proxy
statement/prospectus forms a part, does not cover the resale of shares of
Celgene common stock to be received by Signal's affiliates in the merger.



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<PAGE>

                  THE MERGER AGREEMENT AND RELATED AGREEMENTS

The following description of the merger agreement does not purport to be
complete and is qualified in its entirety by reference to the merger agreement,
a copy of which is attached hereto as Appendix A and incorporated by reference
herein. Shareholders are urged to read the merger agreement in its entirety for
a more complete description of the merger.


GENERAL

THE MERGER. The merger agreement provides that, on the terms and subject to the
conditions of the merger agreement, Celgene Acquisition Corp. will merge with
and into Signal. As a result of this merger, Signal will become a wholly owned
subsidiary of Celgene. In the merger, shareholders of Signal will receive 0.1257
of a share of Celgene common stock, par value $.01 per share, for each share of
Signal common stock (including shares of Signal preferred stock which will be
converted into Signal common stock immediately before the merger). The merger
will become effective upon the filing of an agreement of merger with the
Secretary of State of the State of California, or such other time as the parties
may specify. This filing is anticipated to be made two business days after
receipt of Signal shareholder approval and the satisfaction or waiver of the
other conditions to the merger.


CONSIDERATION TO BE RECEIVED IN THE MERGER

The merger agreement provides that, upon consummation of the merger, each
outstanding share of Signal common stock (including shares of Signal preferred
stock which will be converted into Signal common stock immediately before the
merger), other than shares owned by holders who exercise dissenters' rights
under California law, will be converted automatically into the right to receive
0.1257 of a share of Celgene common stock.

EXCHANGE OF SHARES. As soon as practical after the effective time of the merger,
Celgene will cause to be sent to each shareholder of record of Signal as
representing the effective time of the merger transmittal materials for use in
exchanging certificates of Signal capital stock for certificates representing
Celgene common stock. The transmittal materials will contain information and
instructions on how to surrender Signal capital stock certificates for new
certificates representing Celgene common stock.

No fractional shares of Celgene common stock will be issued to holders of Signal
common stock; instead, Signal shareholders will receive cash for the fraction of
a share of Celgene common stock they would have otherwise received. See "The
Merger Agreement--Conversion of Shares; Procedures for Exchange of Certificates;
No Fractional Shares."

Until a holder of Signal common stock surrenders his, her or its certificates
representing shares of Signal capital stock, the certificates will, after the
effective time of the merger, represent for all purposes only the right to
receive the Celgene common stock specified in the merger agreement.

SIGNAL SHAREHOLDERS SHOULD NOT SURRENDER THEIR STOCK CERTIFICATES FOR EXCHANGE
UNTIL THEY RECEIVE A TRANSMITTAL FORM.


CONDITIONS TO THE MERGER

Under the merger agreement, the respective obligations of each party to effect
the merger are subject to the satisfaction or waiver of each of the following
conditions:

1. the adoption and approval of the merger agreement and the approval of the
   principal terms of the merger by the affirmative vote of the holders of at
   least a majority of the voting power of all outstanding shares of Signal
   common stock and the affirmative vote of the holders of at least a majority
   of the voting power of all outstanding shares of Signal preferred stock (each
   voting as a separate class);

2. the number of shares of Signal common stock into which all dissenting shares
   are convertible will not constitute in excess of 5% of the outstanding shares
   of Signal immediately before the merger;


                                       55
<PAGE>

3.  the Signal preferred shareholders must have approved the conversion of their
    shares of preferred stock into Signal common stock immediately before the
    merger;

4.  Celgene must have received affiliate agreements from each of the affiliates
    of Signal;

5.  Celgene must have obtained a letter from KPMG LLP, Celgene's independent
    public accountants, dated as of the closing date of the merger, with respect
    to Celgene, and from Ernst & Young LLP, Signal's independent public
    accountants, dated as of the closing date of the merger, with respect to
    Signal, to the effect that the merger qualifies for pooling-of-interests
    treatment for financial reporting purposes in accordance with GAAP.

6.  Signal must have terminated or modified any and all agreements with Nippon
    Kayaku Co., Ltd. on terms acceptable to Celgene;

7.  the absence of any law, judgment, order or proceeding preventing completion
    of the merger;

8.  all authorizations, permits, consents, orders or approvals of, or
    declarations or filings with, any governmental entity or other person or
    entity necessary to effect the transactions contemplated by the merger
    agreement must have occurred, been filed or been obtained, as the case may
    be;

9.  each party must have obtained all licenses, franchises, permits, privileges,
    immunities, approvals and other authorizations from all governmental
    entities, whether by transfer, reissuance, modification or otherwise,
    required to be obtained by it in connection with or for the operation of the
    business as presently conducted and contemplated in the merger agreement;

10. the registration statement on Form S-4, of which this proxy
    statement/prospectus forms a part, must have been declared effective by the
    SEC, and there must not be any stop order or proceedings seeking a stop
    order;

11. the other party to the merger agreement must have performed and complied
    with each agreement, covenant and obligation required to be performed or
    complied with by it under the merger agreement;

12. since December 31, 1999, each party must not have suffered any event,
    violation or other matter that would have a material adverse effect on the
    business, condition (financial or otherwise), assets, liabilities,
    operations, properties or prospects of such party;

13. the representations and warranties must be true and correct in all respects
    as of the date of the merger agreement and as of the date of completion of
    the merger with the same effect as though such representations and
    warranties had been made at and as of such time, other than representations
    and warranties that speak as of a specific date or time, which need only be
    true and correct in all respects as of such date or time;

14. each party must have delivered or caused to be delivered to the other party
    each of the items required to be delivered in the merger agreement;

15. key Signal employees must have entered into employment agreements with the
    surviving corporation; and

16. Celgene must have authorized listing on the Nasdaq National Market the
    shares of its common stock to be issued in connection with the merger and to
    be issuable upon exercise of converted Signal stock options and warrants
    which Celgene will assume at the effective time of the merger.


REPRESENTATIONS AND WARRANTIES

The merger agreement contains various customary representations and warranties
of the parties, including the following representations by Signal:

o organization;

o authority relative to the merger agreement;

o capitalization;

                                       56
<PAGE>

o consents and approvals, no violation of law;

o financial statements;

o absence of undisclosed liabilities;

o absence of certain changes or events; material contracts;

o title to properties; encumbrances;

o intellectual property;

o material contracts;

o litigation;

o no default;

o employee benefit plans; ERISA;

o taxes;

o environmental laws and regulations;

o labor matters;

o FDA matters;

o accounting matters;

o opinion of financial advisor;

o compliance with applicable law;

o brokers;

o affiliate transaction;

o tax matters;

o information in disclosure documents and registration statements; and

o vote required.

The following representations were also made by Celgene and Celgene Acquisition
Corp.:

o organization;

o authority relative to the merger agreement;

o capitalization;

o reports and financial statements;

o compliance with applicable law;

o absence of certain changes or events;

o litigation;

o opinion of financial advisor;

o accounting matters;

o tax matters;

o consents and approvals, no violations;

o brokers; and

o information in disclosure documents and registration statement.

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<PAGE>

COVENANTS

NON-SOLICITATION. The merger agreement provides that:

o  Prior to the effective time of the merger, neither Signal, any of its
   affiliates, nor any of the respective directors, officers, employees,
   affiliates, agents or representatives of the foregoing (including, without
   limitation, any investment banker, attorney or accountant retained by Signal)
   will, directly or indirectly, solicit, initiate, facilitate or encourage
   (including by way of furnishing or disclosing non-public information) any
   inquiries or the making of any proposal with respect to or which may
   reasonably be expected to lead to, any merger, consolidation or other
   business combination involving Signal or the acquisition of all or any
   significant portion of the assets or capital stock of Signal, other than the
   merger (any such proposal being referred to as an acquisition transaction) or
   negotiate, explore or otherwise engage in discussions with any corporation,
   partnership, person, other entity or group (as defined in Section 13(d)(2) of
   the Exchange Act) (other than Celgene and its representatives) in furtherance
   of such inquiries or with respect to any acquisition transaction, or endorse
   any acquisition transaction, or enter into any agreement, arrangement or
   understanding with respect to any such acquisition transaction or which would
   require it to abandon, terminate or fail to consummate the merger or any
   other transaction contemplated by the merger agreement;

o  Signal and its affiliates will immediately cease and cause to be terminated
   any existing activities, discussions or negotiations with any person (other
   than Celgene and its representatives) conducted heretofore with respect to
   any acquisition transaction; and

o  Signal will immediately advise Celgene in writing of any such inquiries or
   proposals (or indications of a desire to make a proposal) received by (or
   indicated to), any such information requested from, or any such negotiations
   or discussions sought to be initiated or continued with, any of it, its
   affiliates, or any of the respective directors, officers, employees, agents
   or representatives of the foregoing, in each case from a corporation,
   partnership, person or other entity or group (other than Celgene and its
   representatives) with respect to an acquisition transaction, and the terms
   thereof, including the identity of such third party, and to update on an
   ongoing basis or upon Celgene's request, the status of such inquiry or
   proposal, as well as any actions taken or other developments.

CONDUCT OF BUSINESS PENDING THE MERGER. Under the merger agreement, Signal has
agreed that from the date of the merger agreement until the earlier of the
effective time of the merger and the termination of the merger agreement, it
will not, except as agreed to with Celgene:

o  conduct its business other than in the ordinary and usual course consistent
   with past practice and shall use its reasonable efforts to preserve intact
   the present business organization, keep available the services of its present
   officers and key employees and preserve the goodwill of those having business
   relationships with it;

o  amend its charter, by-laws or other organizational documents or split,
   combine or reclassify any shares of its outstanding capital stock or declare,
   set aside or pay any dividend or other distribution payable in cash, stock or
   property or directly or indirectly redeem or otherwise acquire any shares of
   its capital stock;

o  authorize for issuance, issue or sell or agree to issue or sell any shares
   of, or rights to acquire or convert into shares of, its capital stock
   (whether through the issuance or granting of options, warrants, commitments,
   subscriptions, rights to purchase or otherwise), except for the issuance of
   shares of Signal common stock upon the exercise of Signal stock options
   outstanding on the date of the merger agreement;

o  merge or consolidate with another entity;

o  acquire or purchase an equity interest in or a substantial portion of the
   assets of another corporation, partnership or other business organization or
   otherwise acquire any assets outside the ordinary and usual course of
   business and consistent with past practice or otherwise enter into any
   material contract, commitment or transaction outside the ordinary and usual
   course of business consistent with past practice;


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o  sell, lease, license, waive, release, transfer, encumber or otherwise dispose
   of its material assets,


o  incur, assume or prepay any material indebtedness or any other material
   liabilities other than in the ordinary course of business consistent with
   past practice and other than in connection with borrowing up to $2 million
   under a secured line of credit with MMC/GATX Partnership No.1,


o  assume, guarantee, endorse or otherwise become liable or responsible (whether
   directly, contingently or otherwise) for the obligations of any other person
   other than customers, in each case in the ordinary course of business and
   consistent with past practice,


o  make, extend or modify in any material respect any loans, advances or capital
   contributions to, or investments in, any other person,


o  authorize or make capital expenditures in excess of the respective amounts
   set forth on a schedule to the merger agreement


o  permit any insurance policy naming Signal as a beneficiary or a loss payee to
   be canceled or terminated other than in the ordinary course of business


o  form a subsidiary or enter into any contract, agreement, commitment or
   arrangement with respect to any of the foregoing;


o  adopt, enter into, terminate or amend (except as required by applicable law)
   any Signal employee benefit plan or other arrangement for the current or
   future benefit or welfare of any director, officer, or current or former
   employee or increase in any manner the compensation or fringe benefits of, or
   pay any bonus to, any director, officer or employee (except for normal
   increases in compensation in the ordinary course of business consistent with
   past practice and accrued and unpaid bonuses in respect of Signal's fiscal
   year ended December 31, 1999 that are consistent with past practice and have
   been properly accrued and reflected on Signal's books and records) or take
   any action to fund or in any other way secure or to accelerate or otherwise
   remove restrictions with respect to, the payment of compensation or benefits
   under any employee plan, agreement, contract, arrangement or other Signal
   employee benefit plan (including Signal stock options);


o  take any action with respect to, or make any material change in, its
   accounting or tax policies or procedures, except as required by law or to
   comply with GAAP; or


o  take any action or allow any action to be taken by any of its affiliates
   which would jeopardize the treatment of Celgene's merger with Signal as a
   pooling-of-interests for accounting purposes or take any action which would
   jeopardize qualification of the merger as a reorganization within the meaning
   of Section 368(a) of the Internal Revenue Code of 1986, as amended.


SHAREHOLDERS' MEETING. Under the merger agreement, Signal has agreed to call,
give notice of, convene and hold a meeting of its shareholders on a date as soon
as reasonably practicable in accordance with the California General Corporation
Law and the federal securities law for the purpose of considering and voting
upon the adoption and approval of the merger agreement, the approval of the
principal terms of the merger and the approval of conversion of Signal preferred
stock. Subject to its fiduciary duties under applicable law, Signal has agreed
to take all lawful actions to solicit the approval of the merger by Signal's
shareholders.


OTHER COVENANTS. The merger agreement contains other covenants including
covenants relating to:


o preparation and filing of a proxy statement;


o access to information;


o pooling-of-interests accounting;


o coordination and cooperation with respect to tax matters;


o preparing and filing of disclosure documents;

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o  actions and filings with governmental bodies, agencies, officials or other
   authorities and third parties;

o  public announcements;

o  maintaining books and records;

o  filing of a Form S-4 registration statement;

o  government authorizations; and

o  the listing of the Celgene common stock issued in the merger.

FURTHER ACTION.  The merger  agreement  provides that each of the parties to the
merger  agreement  will use its best  efforts to take all  actions and to do all
other things necessary, proper or advisable to:

o  consummate and make effective as promptly as practicable the transactions
   contemplated by the merger agreement;

o  obtain in a timely manner all necessary waivers, consents and approvals;

o  effect all necessary registrations and filings; and

o  otherwise satisfy or cause to be satisfied all conditions precedent to its
   obligations under the merger agreement.


TERMINATION

The merger agreement provides that it may be terminated and the merger may be
abandoned:

o  at any time before the closing of the merger, by mutual written consent of
   Celgene and Signal;

o  at any time before the closing of the merger, by either Celgene or Signal:

     o  in the event of a material breach of the merger agreement by the
        non-terminating party; or

     o  upon notification to the non-terminating party by the terminating party
        that the non-terminating party has failed to satisfy a condition set
        forth in the merger agreement or in any related agreement contemplated
        in the merger agreement required to be satisfied by such non-terminating
        party prior to or at the closing date of the merger;

o  at any time after December 31, 2000 by either Celgene or Signal if the merger
   has not been consummated by that date. However this right to terminate will
   not be available to any party whose failure to fulfill any obligation under
   the merger agreement has been the cause of or resulted in the failure of the
   merger to occur on or before that date;

o  at any time by either Celgene or Signal if the Signal shareholders do not
   approve the merger; and

o  at any time before the closing of the merger by Celgene:

     o  if the Signal board of directors withdraws or materially amends its
        recommendation to approve the merger or recommends another acquisition
        proposal; or

     o  Signal breaches its agreement not to solicit, encourage, or participate
        in discussions or negotiations, with respect to acquisition proposals
        with parties other than Celgene.

In the event of the termination of the merger agreement, the merger agreement
provides that it will become void and there will be no liability on the part of
any party except that:

(a)  if Signal's board withdraws its recommendation that shareholders vote for
     the merger, or solicits or recommends another acquisition transaction with
     a third party, then Signal will pay to Celgene $10 million dollars
     immediately;

(b)  if Signal breaches a representation or warranty or breaches a covenant,
     then Signal will pay to Celgene $5 million immediately plus an additional
     $5 million if Signal signs or completes another acquisition transaction
     within one year;


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(c)  if the merger is not completed by December 31, 2000 and Celgene terminates
     the merger agreement, or if Signal shareholders do not approve the merger,
     then Signal will pay to Celgene $10 million if Signal signs or completes
     another acquisition transaction with a third party within one year; and

(d)  if Celgene breaches a representation or warranty or breaches a covenant,
     then Celgene will pay to Signal $5 million immediately.

In addition, Celgene's option to purchase shares of Signal common stock and
stock appreciation rights becomes immediately exercisable for one year with
respect to subparagraph (a) and becomes exercisable only if Signal signs or
completes another acquisition transaction within one year with respect to
subparagraphs (b) and (c).

AMENDMENT; WAIVER

The merger agreement may be amended at any time in a writing signed by each of
the parties. Once Signal shareholders have approved the merger, no amendment
that requires further approval by the Signal shareholders may be made without
such further approval.

At any time before the effective time of the merger, a party may in a document
signed by each party:

o  extend the time for performance of any of the obligations or other acts of
   the other parties;

o  waive any inaccuracies in the representations and warranties of the other
   parties contained in the merger agreement or in any document delivered
   pursuant to the merger agreement; or

o  waive compliance, where permissible, with any of the agreements or conditions
   contained in the merger agreement.

FEES AND EXPENSES

Expenses related to the exchange of the shares of Signal common stock in the
merger will be paid by Signal. Expenses incurred in connection with the filing
fee for the registration statement and the printing of the proxy
statement/prospectus and the registration statement will be paid by Celgene.
Otherwise, all fees and expenses incurred in connection with the merger
agreement and the transactions contemplated thereby will be paid by the party
incurring the expenses, whether or not the merger is consummated.

VOTING AND PROXY AGREEMENT

In connection with the merger agreement, Celgene entered into individual voting
and proxy agreements with certain shareholders of Signal. These shareholders
combined represented approximately 56% of Signal common stock and 79% of Signal
preferred stock then outstanding.

The shareholders signing the voting and proxy agreement, among other things,
granted to Celgene an irrevocable proxy to vote their shares of Signal capital
stock in favor of the adoption and approval of the merger agreement, the
conversion of Signal preferred stock to Signal common stock and approval of the
principal terms of the merger and any other transactions contemplated by the
merger agreement. The voting and proxy agreement provides that it will terminate
upon the effective date of the merger and, in any event, any proxy executed
pursuant to the voting and proxy agreement will automatically terminate upon
termination of the merger agreement.

OPTION AGREEMENT

In connection with the merger agreement, Signal entered into an option agreement
with Celgene in which Signal granted Celgene an option to purchase 2,000,000
shares of Signal common stock and stock appreciation rights with respect to
3,000,000 shares of Signal common stock for a cash exercise price of $6.60 per
share, subject to adjustment as described in the option agreement.


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The option agreement provides that Celgene can exercise the option to purchase
all or part of the 2,000,000 shares as follows:

o  if the merger agreement is terminated by Celgene because Signal's board of
   directors withdraws or amends its recommendation or approval of the merger or
   the merger agreement or makes a recommendation with respect to another
   acquisition transaction, Celgene can exercise the option at any time during
   the one year period beginning on the date of such termination; or

o  if the merger agreement is terminated by Celgene because Signal has
   materially breached any of its representations and warranties or covenants or
   agreements under the merger agreement or the merger is not consummated before
   December 31, 2000, or by either Celgene or Signal because the approval of
   Signal's shareholders is not obtained and Signal has directly or indirectly
   entered into a definitive agreement for or has consummated an acquisition
   transaction within one year of such termination, then Celgene can exercise
   the option from the date on which Celgene receives notice of the event
   triggering its right to exercise the option to the date that is three
   business days after the acquisition transaction occurs.

Under the option agreement, if Celgene exercises the option and then sells or
otherwise disposes of the shares, Signal will pay Celgene stock appreciation
rights in the form of an amount in cash equal to 3,000,000 multiplied by the
excess, if any, of the price per share Celgene receives in the sale or
disposition of the shares over $6.60.

The option agreement provides that it will terminate upon the effective date of
the merger or upon termination of the merger agreement other than as described
above. However, if Celgene is prohibited from exercising the option by actions
taken by the Federal Trade Commission or the Department of Justice in connection
with the Hart-Scott-Rodino Antitrust Improvements Act, the option agreement will
not terminate until the earlier of 30 days from the date such prohibition is
removed or six months after the date Celgene's right to exercise the option
would otherwise have terminated.


CONFIDENTIALITY AGREEMENT

Signal and Celgene entered into a confidentiality agreement on May 25, 2000 that
provides for, among other things, the confidential treatment of the discussions
regarding the merger and the exchange of confidential information concerning
Signal and Celgene. Signal and Celgene subsequently entered into a letter of
intent, dated June 22, 2000, that confirmed the obligations contained in the
confidentiality agreement.


AGREEMENT OF SIGNAL AFFILIATES

Rule 145 under the Securities Act of 1933 regulates the disposition of
securities of "affiliates" of Signal in connection with the merger. At least 10
days before the effective date of the merger, Signal will deliver to Celgene a
list identifying all persons who are or may be deemed to be, at the time of the
Signal meeting, "affiliates" of Signal for purposes of Rule 145 under the
Securities Act. This list may be further updated before the effective time of
the merger. Signal has agreed to use its reasonable best efforts to cause each
person who is identified as an affiliate in this list to deliver to Celgene,
before the effective time of the merger, a written affiliate agreement. Under
these affiliate agreements, each affiliate will represent that he, she or it has
been advised that the affiliate may not sell, transfer or otherwise dispose of
Celgene common stock issued to the affiliate in the merger unless the sale,
transfer or other disposition:

(1)  has been registered under the Securities Act;

(2)  complies with the requirements of Rule 145 under the Securities Act;

(3)  in the opinion of counsel reasonably acceptable to Celgene, is otherwise
     exempt from registration under the Securities Act; or

(4)  based on advice to the affiliate from the SEC, will not be the subject of
     SEC action (and the staff of the SEC would not recommend any SEC action)
     with respect to such sale, transfer or other disposition.

In addition, under these affiliate agreements each affiliate has furhter
represented that he, she or it will not sell, transfer or otherwise dispose of
any Celgene common stock  received in the merger until after the publication of
financial statements reflectiong the combined operating results of Signal and
Celgene for a period of not less than 30 days after the merger.



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                          INFORMATION REGARDING CELGENE

MANAGEMENT AND ADDITIONAL INFORMATION

Certain information relating to directors and executive compensation, various
benefit plans, voting securities and principal holders thereof, certain
relationships and related transactions and other related matters as to Celgene
is incorporated by reference or set forth in Celgene's Annual Report on Form
10-K for the year ended December 31, 1999, and its Quarterly Report on Form 10-Q
for the quarterly period ended March 31, 2000, incorporated herein by reference.
Shareholders desiring copies of such documents may contact Celgene at its
address or telephone number indicated under "Where You Can Find More
Information."


                          INFORMATION REGARDING SIGNAL

                          OVERVIEW OF SIGNAL'S BUSINESS

Signal Pharmaceuticals is a biopharmaceutical company focused on discovering and
developing new classes of "small molecule" drugs, which are drugs that can be
taken in pill form, that regulate disease-associated genes. Signal believes its
approach can convert valuable information coming from genomics initiatives into
new classes of superior drugs. Signal's drug discovery engine enables it to
identify and pursue potential gene-regulating drug targets across multiple
diseases and to rapidly identify drugs for development. Signal's efforts are
focused in several major disease areas in which abnormal gene regulation plays
an important role in the development of disease. These disease areas include
cancer, inflammatory disease, osteoporosis, cardiovascular disease, neurological
disease and viral infections.

Signal is conducting its drug discovery and development programs both
independently and with its corporate collaborators: Serono, Byk Gulden, Pliva,
Axys Pharmaceuticals and DuPont Pharmaceuticals. Currently, Signal's corporate
collaborators fund significant portions of its research and development
expenditures. In two of its collaborative programs, Signal has retained United
States co-commercialization or profit-sharing rights for the areas of cancer and
inflammatory disease, and in another collaborative program, Signal has retained
worldwide co-development and commercialization rights.


BACKGROUND


GENES AND DISEASE

The human body contains an estimated 100,000 genes. Genes control all cellular
functions responsible for maintaining human health by serving as blueprints for
the production of proteins in cells, a process known as gene expression.
Proteins, which control a cell's biological function, include hormones, enzymes
and cytokines, which are proteins secreted by cells that regulate the
inflammatory response. Critical cell functions regulated by proteins include
growth, differentiation and survival. Recent advances in cellular and molecular
biology have shown that malfunctions in gene regulation either cause or
predispose humans to most diseases. These malfunctions cause cells to produce
inappropriate amounts or types of proteins. For example, the uncontrolled
proliferation of cells characteristic of cancer and inflammatory diseases is the
result of over-activation of multiple genes and the proteins they produce, such
as cytokines and enzymes. Conversely, under-activation of critical genes and
their protein products, such as tumor suppressors and growth factors, also may
give rise to disease, including cancer and neurological disorders. Many complex
diseases are caused by the abnormal activity of not just one but multiple genes.
Such complex diseases include cancer and inflammatory, cardiovascular and
neurological diseases.


REGULATION OF GENES BY GENE SWITCHES

Gene regulation is a highly controlled process in which specific sets of genes
are switched on and off in select tissues to maintain the body's essential
functions. Genes are controlled by networks of proteins inside cells which relay
information through pathways from a cell's surface to its nucleus


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where genes are expressed. These pathways consist of several large and distinct
classes of gene regulating proteins, or gene switches, which include
transcription factors, kinases and ligases. Transcription factors are molecular
switches that bind to the regions of genes that control the level and duration
of gene expression and protein production. Kinases are enzymes that transmit
information within cells and ultimately lead to gene expression. Ligases control
the proper levels of gene regulating proteins in cells. Each of these three
classes of gene switches can control not just one but multiple genes that
contribute to disease. Therefore, drugs designed to target these gene switches
at pivotal points in a gene regulating pathway can have a major impact on the
subsequent expression of entire sets of genes that contribute to disease.


Genomics is the large-scale identification and sequencing of the genes that
comprise the human genome. Currently this information is being compiled in
databases, and sequencing of the entire human genome is nearing completion. This
genomic database provides a starting point for understanding the underlying role
of genes in disease, but by itself is inadequate to identify key disease-related
gene switches. To realize the substantial potential of genomics initiatives, key
gene switches involved in disease need to be identified to permit the rapid
development of superior drug therapies that regulate disease-associated genes.


SIGNAL'S GENE REGULATING DRUGS


Signal has developed and integrated a large set of target and drug discovery
technologies to accelerate the application of genomics to the discovery of
important new classes of gene regulating drugs. Signal first maps select gene
regulating pathways to identify drug targets, or gene switches, that control
specific genes that cause disease. This information is then used to discover
novel gene regulating drugs by applying Signal's drug discovery engine. This
engine consists of:


o  Advanced cellular, molecular and genomic technologies. Signal uses
   information produced from human genomics initiatives to map gene regulating
   pathways and identify clinically important drug targets for specific
   diseases. Signal has generated proprietary human cell lines, from multiple
   tissues of the body, to create in vitro, or test tube, models of disease and
   to evaluate the activity and selectivity of drug candidates. Signal also uses
   functional genomics and proteomics, which is the large-scale linking of genes
   and their protein products to their biological functions, for mapping gene
   regulating pathways and identifying disease targets for use in drug
   discovery;


o  High throughput screening systems and diverse compound libraries. Signal has
   assembled a library of more than 200,000 distinct small molecule compounds
   and natural products which it screens using its biochemical and cell-based
   screening technologies. Signal's screening systems include a technology for
   simultaneously screening multiple kinases to provide drug activity and
   specificity data across multiple drug targets;


o  A proprietary, specially designed kinase inhibitor library. Signal identified
   the active sites, or molecular locks, on a number of gene regulating kinase
   targets using its extensive knowledge of the three dimensional structures of
   these targets. Signal believes gene regulating targets identified in the
   future will contain similar locks. Signal's kinase inhibitor library is
   designed to contain compounds expected to fit like molecular keys into these
   locks, enhancing Signal's ability to identify effective inhibitors of
   current, as well as yet-undiscovered, gene regulating targets. In addition,
   Signal designs these compounds to have attractive pharmaceutical properties,
   such as solubility, chemical stability, non-reactivity and the ability to be
   taken in pill form; and


o  Structure-based drug design. Signal uses its proprietary three-dimensional
   models of drug targets, combined with advanced chemistry technologies, to
   efficiently generate drug leads and advance drug candidates into preclinical
   and clinical development.


Signal believes that, together, these integrated target and drug discovery
capabilities enable it to proceed rapidly from target identification to
screening and optimization of drug candidates. To date, Signal alone or with its
collaborators has identified 27 drug targets in 10 gene regulating pathways



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with potential applications in at least six major disease areas. Signal also has
developed 29 drug discovery screens, identified 23 drug leads and commenced
evaluation of drug leads in 15 animal models of disease. Signal has developed
one preclinical drug candidate in its cancer program.


SIGNAL'S DRUG DEVELOPMENT PROGRAMS


Signal's drug discovery and development programs are focused in several disease
areas in which gene dysregulation plays a major role in the onset and
progression of disease. These diseases include cancer, inflammatory disease,
osteoporosis, cardiovascular disease, neurological disease and viral infections.


CANCER PROGRAMS


Cancer is a group of diseases characterized by uncontrolled growth and spread of
abnormal cells in the body. Cancer results from abnormalities in the expression
of genes that regulate cell proliferation, cell migration and cell death. Most
current anti-cancer drugs kill both cancerous and normal cells, giving rise to
serious toxic side effects. Signal is developing new classes of drugs designed
to selectively control abnormal gene regulating pathways which cause the start
or spread of cancer, with the goal of creating safer and more effective cancer
therapies.


Signal has five drug discovery and development programs focused on regulating
abnormal gene expression involved in the onset and progression of cancer. Signal
currently has one drug candidate, SP8490, in preclinical development for
preventing and treating breast cancer and other cancers. To date, Signal has not
filed an IND for this drug candidate. Signal also has three additional series of
drug leads for the potential treatment of cancer.


Estrogen Gene Regulation in Cancer


Estrogen is a hormone that has a broad spectrum of effects on tissues in both
women and men. Many of these biological effects are beneficial, including
maintenance of bone density and cardiovascular and neurological protection. In
addition to estrogen's positive effects, however, the hormone also is a potent
growth factor in the breast and uterus that has been demonstrated to increase
significantly the risk of cancer in women. In addition, estrogen contributes to
prostate cancer in men.


Two distinct estrogen receptors exist in the body, the estrogen receptor-alpha,
or ER-, and the estrogen receptor-beta, or ER-, each of which has a distinct
tissue distribution in the body. ER- is found predominantly in bone and in
cardiovascular, breast and reproductive tissue, while ER- is the predominantly
expressed estrogen receptor in the prostate and hippocampus region of the brain.
Given the tissue-selective expression of ER- and ER-, estrogen receptor
modulators potentially can be designed to mimic the positive effects and block
the negative effects of estrogen in different tissues. Drugs that modulate these
receptors are termed selective estrogen receptor modulators, or SERMs.


Unlike chemotherapeutic agents which often cause significant toxic side effects,
SERMs act through different, primarily non-toxic mechanisms. Currently two SERMs
are marketed for treatment of breast cancer. One of these SERMs, tamoxifen, is
the most widely prescribed anti-hormonal therapy for cancer today. However,
tamoxifen is associated with a number of adverse side effects, including an
increased risk for uterine cancer, blood clotting and hot flashes. In addition,
virtually all patients receiving tamoxifen become resistant to the drug.


Signal is using its gene  regulation  expertise to design new classes of ER- and
ER--selective  SERMs with efficacy and safety profiles that Signal believes will
be  superior  to those of many  current  chemotherapies  and  tamoxifen.  Signal
believes  these SERMs have  significant  potential for  preventing  and treating
breast, endometrial, prostate, colon and other cancers whose growth is dependent
on estrogen.


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SP8490 -- An ER- Modulator

Using its drug discovery engine and expertise in estrogen gene regulating
pathways, Signal has discovered and is developing a series of SERMs with
improved efficacy and safety in animal models when compared with tamoxifen. In
animal studies, these drug leads were orally effective in preventing breast
cancer and demonstrated equal or superior efficacy to tamoxifen. Additionally,
these compounds displayed a superior safety profile on uterine tissue compared
to tamoxifen. A potential drug candidate, SP8490, currently is in preclinical
development.


ER- Modulators

Signal has discovered and is developing a novel series of ER--selective SERMs
which currently are undergoing lead optimization. Signal's SERM-\S drug leads
represent a novel series of SERMs that, if successfully commercialized, may be
useful in treating the large number of cancer patients that develop ER--positive
cancers such as prostate, colon, ovarian and tamoxifen-resistant breast cancer.

In October 1999, Signal entered into a collaboration with Axys Pharmaceuticals
to discover and develop ER--selective SERMs for cancer therapy. This
collaboration and Signal's other collaborative arrangements are described below
under the heading "Corporate Collaborators."


JNK Inhibitors for Cancer

The cJun N-terminal kinase, or JNK, pathway controls the expression of specific
sets of genes involved in cancer, including:

o  cytokines and growth factors that promote the growth of cancer cells;

o  molecules on the surface of cells that are responsible for cell-to-cell
   attachment;

o  tissue-destructive enzymes that enable tumors to spread to distant sites in
   the body and invade normal tissues and organs, referred to as metastasis; and

o  factors that lead to the growth of new blood vessels and aid in establishing
   new tumors, referred to as angiogenic factors.

Signal is applying its expertise in the JNK gene regulating pathway to identify
novel cancer targets which play a fundamental role in tumor growth and to design
new classes of drugs that target abnormalities in the JNK gene regulating
pathway to inhibit the transformation, growth and spread of cancer. Using its
drug discovery engine, Signal has identified potent and selective small molecule
inhibitors of the JNK pathway which have demonstrated anti-proliferative
activity in tumor cell lines in vitro.


NF-kB Inhibitors for Cancer

The nuclear factor kappa B, or NF-kB, pathway controls the expression of
specific sets of genes involved in different stages of cancer development and
progression. These include specific cell survival factors that make cancer cells
resistant to radiation and chemotherapy. Using its gene regulating target
discovery expertise, Signal and its collaborators have mapped the NF-kB pathway
extensively and have identified multiple targets in the NF-kB gene regulating
pathway for use in drug discovery. Signal and its collaborators also have
demonstrated in vitro that inhibiting key NF-kB kinase targets significantly
increases the sensitivity of cancer cells to cancer chemotherapeutics. Signal
has identified small molecule inhibitors of a specific kinase target in the
NF-kB gene regulating pathway and is optimizing the pharmaceutical properties of
these drug leads. Signal plans to study these drug leads further in animal
models of cancer.

In November 1997, Signal entered into a collaboration with Serono to discover
and develop drugs that target the NF-kB pathway for the potential treatment of
certain cancers and other diseases.

Ligase Inhibitors for Cancer

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Signal has discovered and validated in vitro ligase drug targets in the NF-kB
and other important gene regulating pathways. Ligases represent an important new
family of gene regulating targets because of their ability to precisely maintain
normal levels of proteins in cells. In cancer, certain proteins, such as those
that suppress the growth of tumors, are lost or diminished which causes the
progression of cancer. Signal has developed novel drug screens to identify
selective ligase inhibitors which Signal believes may restore normal levels of
proteins the body uses to prevent the emergence of cancer and resistance to
chemotherapy.


INFLAMMATORY DISEASE PROGRAMS

The human immune system is comprised of cells and biochemical substances that
protect the body from infectious organisms, physical injury and abnormal
cellular events such as cancer. Key components of the immune system, such as
white blood cells, are responsible for protective or inflammatory responses at
sites of injury and disease. Inflammatory diseases arise from over-activation of
the immune system resulting in the over-production of immune cells, inflammatory
proteins and tissue-destructive enzymes. These cells and proteins attack and
destroy healthy tissue, giving rise to a number of diseases such as rheumatoid
arthritis, osteoarthritis, allergies, asthma, inflammatory bowel disease and
psoriasis, as well as transplant rejection. Many current anti-inflammatory drugs
have dose-limiting side effects and only target a single disease mechanism. More
importantly, although these current drugs alleviate many symptoms of disease,
they generally do not target the underlying mechanisms and therefore do not
effectively modify disease processes or treat the underlying disease.

Signal is identifying drug targets in key inflammation pathways and screening
for new classes of small molecule drugs that regulate inflammatory diseases at
the level of gene function. Signal is optimizing, or plans to optimize,
inhibitors of gene regulating targets in three distinct inflammation pathways,
JNK, NF-kB and p38, and has demonstrated the efficacy of one series of drug
leads in animal models of asthma and arthritis.


JNK Inhibitors for Inflammatory Diseases

Activation of the JNK gene regulating pathway increases the expression of a set
of clinically important inflammatory genes, including tumor necrosis factor
alpha, or TNF, interleukin-2, or IL-2, and gamma interferon. There are multiple
types of the JNK regulatory enzyme, each of which controls the expression of
genes in specific cells and in response to specific stimuli. Signal has eight
issued United States patents, four issued foreign patents and related patent
applications covering JNK, its use in drug discovery and JNK inhibitors.
Over-activation of JNK causes or exacerbates several inflammatory and autoimmune
diseases, including rheumatoid arthritis, asthma and multiple sclerosis.

Signal has developed and initiated high throughput screening for JNK1, JNK2 and
JNK3 inhibitors using proprietary biochemical and cell-based screens. Using its
kinase-focused inhibitor library, Signal has identified several potent compounds
that inhibit JNK1 and JNK2 activity. In addition to significantly reducing
inflammation, one of these drug leads prevents the destruction of joints in an
animal model of arthritis. This drug lead also demonstrates potent
disease-modifying activity in an animal model of asthma. Signal currently is
optimizing drug leads to improve the potency, selectivity and other
pharmaceutical properties of its JNK inhibitors. Signal also is developing
additional high throughput drug screens for several other drug targets in the
JNK pathway, including JNKK1 and JNKK2.


NF-kB Inhibitors for Inflammatory Diseases

NF-kB plays a pivotal role in inflammatory disease processes by regulating
cytokine genes, such as TNF, IL-1, IL-2, IL-6, IL-8, along with genes that code
for molecules on the surface of cells and the cyclooxygenase-2 or, COX-2,
inflammatory enzyme. Signal's researchers and collaborators have identified six
drug targets that regulate NF-kB activation. Signal's discovery of three of
these targets was reported in the journals Science, Nature and Cell. Signal
believes drugs that inhibit NF-kB and


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the activation of select disease-associated genes will have potential disease
modifying effects. Signal has been issued four United States patents and it,
along with its collaborators, has filed related patent applications for targets
in this pathway.

Signal has developed and initiated high throughput screening for NF-kB
inhibitors using proprietary biochemical and cell-based screens. Signal also has
developed technology for profiling the effects of active compounds on a number
of immune-inflammatory genes and proteins in cells and animals. Using its kinase
inhibitor library, Signal has identified several small molecule drug leads which
selectively inhibit a kinase target in the NF-kB pathway. One of these drug
leads potently inhibits expression of the TNF inflammatory response gene in an
animal model. Signal is optimizing these drug leads to further enhance potency,
specificity and bioavailability and is developing additional high throughput
drug screens for other targets in the NF-kB pathway.

In November 1997, Signal initiated a collaborative development and license
agreement with Serono to discover novel NF-kB inhibitors for inflammatory and
other diseases.


p38 Inhibitors for Inflammatory Diseases

Activation of the p38 gene regulating pathway causes the expression of multiple
cytokine genes, including IL-1, IL-6, IL-8 and TNF, which regulate the
development and proliferation of cells in response to disease and tissue injury.
When inappropriately activated, the p38 pathway is believed to play an important
role in diseases arising from abnormal production of cytokines, including heart
disease caused by harmful inflammatory events. To date, Signal and its academic
collaborators have identified five proprietary drug targets in the p38 pathway.
One of these targets is p38-2, a subtype of p38, which is highly expressed in
heart and skeletal muscle and not in most other tissues. Signal and its
collaborators have been issued four United States patents for three drug targets
in the p38 pathway, MKK3, MKK6 and p38-2, and have filed related patent
applications with regard to other potential drug targets in this pathway. In the
p38 pathway, Signal has screened two targets using its kinase inhibitor compound
library and has identified novel inhibitors which it plans to optimize as drug
leads.


OSTEOPOROSIS PROGRAM

The incidence of osteoporosis and bone fractures in women is significantly
increased during and following menopause. Estrogen has been used for hormone
replacement therapy, or HRT, for many years to prevent osteoporosis and
alleviate some of the other effects of menopause. However, HRT has several
negative side effects, including the increased risk of breast and uterine
cancer, which make it a poor treatment option for many women.

ER- Modulators for Osteoporosis

SERMs are designed to mimic the beneficial effects of estrogen by inhibiting
bone loss in postmenopausal women, while avoiding some of estrogen's negative
effects. In 1998 Eli Lilly's raloxifene became the first and only FDA-approved
SERM for osteoporosis.

Signal has developed a novel series of ER--selective SERMs with superior
efficacy and safety when compared with raloxifene in preclinical animal studies.
In three separate animal studies, four of Signal's drug leads were tested in
comparison with estrogen and raloxifene for the ability to inhibit bone loss. In
those studies, Signal's orally administered drug leads were demonstrated to be
significantly superior to raloxifene in preventing bone loss and in preserving
bone strength. Signal's drug leads also demonstrated a superior safety profile
in uterine tissues, when compared with raloxifene. An additional safety feature
of Signal's drug leads is that they do not stimulate cell proliferation in
breast tissue. Signal's ER--selective SERMs also demonstrated a favorable
cholesterol-lowering profile in animal models. The drug leads are well tolerated
in animals and have not shown any negative effects in genetic safety tests
required by the FDA. These drugs, if successfully developed, would provide
clinicians with an alternative, non-estrogen treatment for osteoporosis that
also would minimize some of the adverse effects associated with HRT, including
an increased risk of breast and uterine cancer.


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CARDIOVASCULAR DISEASE PROGRAMS

Many cardiovascular diseases, including heart attack and congestive heart
failure, occur because of abnormal expression of genes in blood vessels and in
the heart. Heart attacks can occur when the cells that line blood vessels are
activated by injury or trauma. These damaged cells overproduce inflammatory
proteins such as molecules on the surface of cells that are responsible for
cell-to-cell attachment, growth factors and cytokines that lead to a buildup of
inflammatory cells and platelets in blood vessel walls. This buildup may block
normal blood flow and lead to atherosclerosis and heart attack. Many of these
proteins are controlled by the NF-kB, JNK and p38 gene regulating pathways. In
addition, the gradual increase of cholesterol in blood vessels may also cause
atherosclerosis and heart attacks. Estrogen enhances the clearance of bad
cholesterol from the blood by regulating gene expression in the liver.

Signal has identified several selective inhibitors of gene regulating targets in
the JNK, NF-kB and estrogen pathways. Signal has developed additional screens
which use proprietary human vascular cell lines to evaluate the potential
cardioprotective effects of its drug leads. Signal plans to test these
inhibitors in various animal models of cardiovascular disease.


JNK Inhibitors for Cardiovascular Disease

Heart failure can occur when muscle cells in the heart fail due to a massive
influx of inflammatory cytokines such as TNF. As a result, the heart fails to
adequately pump blood to the body. The JNK pathway is a key regulator of TNF
gene expression and protein production. This pathway becomes over-activated in
cardiac tissue when the heart undergoes damage or other stress. Signal has
identified selective and potent inhibitors of the JNK pathway that are expected
to undergo evaluation in models of cardiovascular disease.


NF-kB and p38 Inhibitors for Cardiovascular Disease

Restenosis, or the narrowing of blood vessels that restricts blood flow, can
occur when cells that line the inside of blood vessels are over-stimulated
during balloon angioplasty procedures. This often causes the over-expression of
growth factor genes and subsequent over-proliferation of smooth muscle cells in
the blood vessel wall leading to a re-blocking of the blood vessel. NF-kB and
p38 pathways have been demonstrated to be over-activated in animal models of
angioplasty-induced restenosis. Signal has identified several inhibitors of
targets in these pathways that it intends to evaluate in models of
cardiovascular disease.

In November 1997, Signal entered into a collaboration with Serono to develop
inhibitors of NF-kB for potential treatment of cardiovascular and other
diseases.


Estrogen Gene Regulation for Cardiovascular Disease

Signal is applying multiple gene discovery technologies to identify gene
regulating drugs for preventing and treating cardiovascular diseases, including
its proprietary functional genomics technology known as PhaRMA(TM). Signal has
used these technologies to identify over 75 human genes that are regulated by
estrogen in human cardiovascular cells. Many of these genes are regulated by
estrogen in a tissue-selective manner. In addition, Signal has developed and
implemented a proprietary cell-based screening platform for profiling gene
expression in panels of estrogen-regulated genes in cardiovascular cells. These
advanced technologies have led to the discovery and development of new SERMs
which Signal believes will be cardio-protective.


NEUROLOGICAL DISEASE PROGRAMS

The human nervous system consists of two distinct components: the central
nervous system, or CNS, which includes the brain and spinal cord, and the
peripheral nervous system, or PNS, which includes all nerves outside the CNS.
Defects or damage in the CNS can lead to Parkinson's disease, Alzheimer's
disease, stroke or epilepsy, as well as psychiatric disorders such as depression
and schizophrenia. PNS disorders can lead to acute and chronic pain, and
peripheral neuropathies caused by chemotherapy and diabetes can cause chronic
sensory or motor defects.


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Signal's researchers and collaborators have developed a proprietary cell
immortalization technology for producing cloned human neuronal cells that can be
designed to mimic important features of normal and diseased neurons and can be
used for target and drug discovery. Signal has engineered human neuronal and
other cell lines of the CNS and, Signal believes, the first human sensory
neuronal cell lines of the PNS. Unlike many other approaches, Signal's cell
lines are readily renewable and therefore are amenable to the application of
advanced genomic technologies for target and drug discovery.


JNK3 Inhibitors for Neurological Disease

Signal is applying its expertise in engineering neuronal cell lines and in
mapping the JNK gene regulating pathway to identify novel drug targets and drug
leads for neurological diseases. JNK3 is known to be located primarily in the
brain and mice engineered to be deficient in JNK3 are resistant to
experimentally induced epilepsy and stroke. For these reasons, Signal believes
JNK3 inhibitors will have therapeutic value for treating epilepsy, as well as
neurodegeneration associated with Alzheimer's disease, Parkinson's disease,
stroke and head trauma. Using its high throughput screening, Signal has
identified potent and selective inhibitors of the JNK gene regulating pathway,
including the JNK3 drug target. Signal also has demonstrated that one of its
drug leads can block seizures in an animal model of epilepsy and can prevent
neuronal cell damage in a cellular model of Parkinson's disease. Current efforts
are focused on further enhancing potency, selectivity and other pharmaceutical
properties of Signal's drug leads for preclinical development.


VIROLOGY PROGRAMS

Viruses are microorganisms that infect cells and can cause serious disease.
Despite the high incidence of chronic viral infections, only a limited number of
antiviral drugs have been approved to date. New classes of antiviral treatments
are needed which act on novel, virus-specific gene regulating targets while
overcoming problems of toxicity and viral resistance.

Signal's virology program is directed toward four viral gene regulating targets:
two regulatory factors for the hepatitis C virus, or HCV, a transcription factor
for human immunodeficiency virus, or HIV, and the E2 transcription factor for
the human papilloma virus, or HPV. Signal and its collaborators have validated
each of these targets in vitro. Signal has developed a proprietary viral
infection screen for identifying novel inhibitors of HPV gene activation. Signal
has developed target-specific screens for small molecule HCV and HIV inhibitors
as part of its three-year collaboration with DuPont Pharmaceuticals initiated in
December 1997, and compounds with selective antiviral activity have been
identified. In December 1999, DuPont Pharmaceuticals paid Signal a $1 million
equity milestone for the successful development of three novel high throughput
screening drug discovery screens for HCV and HIV antivirals.


ENGINE FOR DISCOVERING GENE REGULATING TARGETS

Signal is developing and applying advanced cellular, molecular and genomic
technologies to discover clinically important targets that are the focus of its
drug discovery programs and corporate collaborations. These discovery
technologies include:

Proprietary Human Cell Lines. Signal has developed a proprietary technology to
immortalize and engineer human cells for use in its target and drug discovery
programs. These cell lines are designed to include the relevant genes and
related pathways involved in both normal and abnormal cellular functions. Signal
uses proprietary human cell lines to develop in vitro models of important
disease processes, including bone metabolism, cardiovascular and
neurodegenerative disease. Signal then uses these human cell lines to identify
and validate novel disease-related genes and specific drug targets in gene
regulating pathways and in screens for drug discovery.

Functional Genomics and Proteomics. Signal applies functional genomics and
proteomics to determine the role specific genes and their protein products play
in health and disease. Signal has implemented advanced genomic technologies to
accelerate the identification and prioritization of gene regulating


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disease targets. Signal has developed and filed a patent for its proprietary
PhaRMA(TM) genomics system, which is a technology to rapidly determine the
differences in gene expression between normal and diseased tissue and to
evaluate the effects of drug candidates on relevant genes within a cell or
tissue. To map the gene regulating pathways involved in specific diseases,
Signal is developing capabilities that integrate protein separation and
analysis. Signal uses these gene and protein discovery tools, in combination
with its proprietary cell lines, to generate a more comprehensive profile of
gene regulating pathways involved in diseases and to facilitate the rapid
identification of novel and specific therapeutic targets. For example, Signal is
applying functional genomics technologies to identify and characterize the role
of genomic targets and their regulatory pathways in cancer, inflammation, bone
metabolism, cardiovascular and neurological diseases.


Pathway Mapping and Target Identification. Signal applies cellular, molecular
and genomic techniques to elucidate the regulatory pathways of disease-related
genes. An initial step in this process involves mapping the regulatory regions
of disease-related genes to identify which transcription factors selectively
activate or inhibit each gene's expression. Signal then uses genomics and
proteomics to identify and characterize specific enzymes or other targets in a
pathway that regulate the activation of these transcription factors. When novel
gene regulating enzymes or other targets are identified, Signal applies advanced
computer programs to search proprietary and public gene databases and to
identify subtypes of these targets with distinct therapeutic applications and
specificity for different tissues. After a potential target has been identified,
Signal uses various techniques to validate the role of newly identified
molecular targets in specific disease processes and to determine their utility
for drug discovery.


ENGINE FOR DISCOVERING AND DEVELOPING GENE REGULATING DRUGS

Once key gene regulating drug targets are identified, Signal uses its advanced
drug discovery engine to rapidly discover and optimize drugs active on these
targets. These drug discovery technologies comprise:

Assay Development. Signal develops and uses biochemical and cell-based assays to
screen for compounds that regulate gene expression in a target- and
cell-specific manner. Signal's researchers have designed modular systems for
developing biochemical and cell-based assays, enabling Signal to substitute
different drug targets into standardized assay formats for use in various
discovery programs. Signal develops and uses biochemical assays to screen
compounds for activity on specific targets. These biochemical assays are
designed to mimic the functional activity of a drug target in its native
cellular environment. Signal's cell-based assays facilitate the identification
of compounds that modulate gene expression through distinct pathways and in
specific cell types. Signal has developed 29 drug discovery assays and is
continuing to develop additional high throughput screening assays.

High Throughput Screening. Signal uses automated, high-volume drug discovery
systems, known as high throughput screening, or HTS, systems for rapid,
target-specific screening of diverse compound libraries. These robotic systems
enhance the precision, reproducibility and integration of chemical and
biological data. Signal's screening library currently consists of more than
200,000 distinct compounds, which include small molecules, natural products and
compounds derived from combinatorial chemistry.

Signal's Kinase Inhibitor Library. Based on its knowledge of the three
dimensional structures of gene regulating targets, Signal has designed a large,
proprietary collection of compounds focused on kinase-binding small molecules.
This library currently consists of approximately 18,000 distinct drug-like
compounds, and Signal plans to continue expanding this proprietary
kinase-focused library. To date Signal has screened the library against seven
kinase gene regulating targets, and has successfully identified inhibitors with
attractive pharmaceutical properties for each of these targets.

Optimization and Preclinical Development of Drug Candidates. Signal develops
drug candidates by integrating its chemistry and pharmacology expertise. Signal
uses traditional medicinal chemistry approaches in conjunction with
combinatorial and computational chemistry to optimize potential drug candidates.
Signal further expedites the drug optimization process by employing
structure-based drug


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design techniques, which are techniques that use computer models of drug targets
to design drug candidates that interact more precisely with a target. Signal's
scientists have designed computer-generated three-dimensional models of the
JNK2, JNK3, ER-- and ER-- drug targets.


Throughout the drug optimization process Signal's chemists are guided by results
from efficacy, drug absorption, distribution, metabolism and safety studies
conducted by Signal's pharmacology and preclinical development group.


CORPORATE COLLABORATORS


Collaborative arrangements with pharmaceutical and biotechnology companies are
an integral part of Signal's business strategy. As of March 31, 2000, Signal had
received approximately $43.3 million in up front fees, research and development
funding, milestone payments and equity investments from its past and current
collaborators. Signal had a collaboration with Nippon Kayaku, which was
terminated in July 2000, a collaboration with Organon, which expired in July
1999, and a collaboration with Tanabe, which was terminated in March 1998. In
connection with the termination of its collaboration with Nippon Kayaku, Signal
granted Nippon Kayaku a worldwide, royalty-free license to a compound the two
parties term NSP6783 and other compounds involved in the collaboration. The
license is exclusive in the field of diagnosing, treating or preventing diseases
of the central and peripheral nervous systems and is non-exclusive in all other
fields. In connection with the termination of its collaboration with Tanabe,
Signal licensed exclusive worldwide rights for a drug lead to Tanabe. In
addition, the research phase of Signal's collaboration with Roche Bioscience
expired in August 1999, and Roche has exclusively licensed two immortalized PNS
cell lines from Signal for use in drug discovery for pain, incontinence and
peripheral vascular disease.


SERONO


In November 1997, Signal entered into a collaborative agreement with Serono,
under which Serono agreed to fund specified research for an initial three-year
period and which contained provisions for extensions to the initial research
term as further described below. The Serono collaboration is focused on
identifying compounds that modulate NF-kB gene regulating pathways to which
Serono has rights for all diseases. The original agreement granted Serono
exclusive rights to these compounds in all countries of the world except Asia.
In April 1999, Serono expanded the collaboration to include Asia by making a
$2.0 million license payment to Signal and agreeing to pay Signal milestones and
royalties for products commercialized in Asia. Under the original agreement,
Serono purchased approximately $10.1 million of Signal's Series E and Series F
preferred stock. Serono also agreed to provide Signal with annual research and
development support. In addition, Serono is obligated to make payments to Signal
based on the achievement of specified research and development milestones and to
pay Signal royalties on future sales of products licensed under the
collaboration. As of March 31, 2000, Serono had paid Signal $8.0 million in
research and development support.


Under an exclusive license that Signal granted to Serono, Serono will be
responsible for preclinical and clinical development of drug candidates and the
development of any drugs arising from the collaboration in all countries of the
world. Signal has co-promotion rights for all products marketed in the United
States, which are exercisable at any time during the term of the agreement and
up to 30 days following receipt of notice from Serono of the filing of an NDA or
equivalent regulatory application, with respect to products arising from the
collaboration. If Signal exercises its co-promotion rights, it will forego
royalties in exchange for a share of product revenue and Signal will be
obligated to reimburse Serono for Signal's share of development costs out of a
portion of revenue.


Under the original agreement, following the expiration of the initial three-year
research term, Serono's research support obligations were to continue for
additional three-year periods, unless terminated by Serono by written notice
given to Signal at least six months prior to the end of the first three-year
term or any subsequent three year term. In February 2000, the parties amended
the agreement to effectively extend the initial three-year research term by one
year and to provide


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Serono with the right to terminate the collaborative research by written notice
given to Signal at least three months prior to the end of this one-year
extension or any subsequent one-year extension. Serono may also terminate the
agreement upon six months' notice any time after the end of the initial
three-year term.


AXYS

In October 1999, Signal entered into a collaborative agreement with Axys
Pharmaceuticals, under which Axys agreed to fund specified research at Signal's
facility for two years. The agreement may be extended for an additional year at
Axys' option. The collaboration with Axys is focused on the discovery and
development of ER--selective SERMs for cancer therapy. Signal has rights for all
indications outside of cancer. Axys has exclusive worldwide development and
marketing rights to Signal's ER--selective SERMs for the treatment of cancer.
Axys will provide payments to Signal in the form of research funding at a level
approximating Signal's cost of this program, research milestones and royalties.
Signal may exercise a profit-share option in the United States and possibly
other territories at a predetermined point during development in lieu of
royalties on product sales. If Signal exercises this right, it will share
equally in the profits in the United States on product sales by Axys but will be
responsible for an equal share of the remaining development and
commercialization costs in the United States. Either party may terminate this
agreement in the event a material breach by the other party remains uncured for
90 days. As of March 31, 2000, Axys had paid Signal $2.0 million in license fees
and approximately $691,000 million in research funding.


DUPONT PHARMACEUTICALS

In December 1997, Signal entered into a collaborative agreement with DuPont
Pharmaceuticals, under which DuPont Pharmaceuticals agreed to fund specified
research at Signal's facility for three years. DuPont Pharmaceuticals has the
option to extend the research term for up to three additional years. The DuPont
Pharmaceuticals collaboration is focused on identifying compounds for the
treatment or prevention of HCV and HIV infections, and Signal has granted DuPont
Pharmaceuticals worldwide exclusive rights to these compounds. Under this
collaboration, Signal and DuPont Pharmaceuticals are responsible for developing
target-specific screening assays and are jointly responsible for identifying
lead compounds. DuPont Pharmaceuticals is solely responsible for lead
optimization and the worldwide development and commercialization of any drugs
arising from the collaboration.

DuPont Pharmaceuticals agreed to provide Signal with annual research and
development support at a level approximating Signal's cost of these programs.
DuPont Pharmaceuticals also is obligated to make payments to Signal upon the
achievement of specified research and development milestones and to pay Signal
royalties on any future product sales arising from the collaboration. This
agreement may be terminated by either party upon 60 days written notice upon a
material breach that remains uncured or upon the bankruptcy of the other party.
DuPont Pharmaceuticals paid Signal a license fee of $1.0 million and, through
March 31, 2000, had paid Signal $4.1 million to support research and development
efforts. In December 1999, DuPont Pharmaceuticals purchased 288,708 shares of
Signal's Series F-1 preferred stock for an aggregate purchase price of $1.0
million, under terms specified in the original agreement in December 1997. This
represented a milestone payment for Signal's successful development and
validation of three new antiviral drug discovery assays, each of which is
designed to identify small molecule inhibitors of key HCV and HIV viral targets.


BYK GULDEN

In June 2000, Signal entered into a collaborative agreement with Byk Gulden
Lomberg Chemische Fabrik GmbH focused on the discovery and optimization of
inhibitors of an unspecified kinase target being investigated by Byk Gulden.
Under the terms of the agreement, Signal will be responsible for constructing a
molecular model of the kinase target and for screening its proprietary kinase
inhibitor library to identify selective and specific inhibitors of this target.
Byk Gulden is obligated to pay Signal a license fee of $250,000 and has agreed
to fund specified research as part of this effort for three


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months and has the right to extend this for an additional  nine-month period. If
Byk  Gulden  extends  the  research  funding,  Signal  will be  responsible  for
optimizing  library hits using  medicinal  chemistry to generate lead compounds.
Byk Gulden also is obligated to make payments to Signal upon the  achievement of
specified pre-clinical,  clinical and commercialization milestones. In addition,
Signal will retain the right to modify any compound  discovered  or generated to
identify  inhibitors  of other  targets  in the same  kinase  family,  and those
inhibitors will be owned exclusively by Signal.  Either party may terminate this
agreement  upon the  bankruptcy,  insolvency,  dissolution  or winding up of the
other  party,  or in the event a  material  breach by the  other  party  remains
uncured for 60 days.


PLIVA

In July 2000, Signal entered into a collaborative agreement with Pliva d.d.
focused on the discovery and optimization of inhibitors of two unspecified
kinase targets being investigated by Pliva. Under the terms of the agreement,
Signal will be responsible for screening its proprietary kinase inhibitor
library, and possibly its diversity library, to identify selective and specific
inhibitors of each of these two targets. Pliva will pay Signal a license fee and
payments based on the achievement of specified research and development
milestones. In addition, if specified research milestones are achieved, Pliva
will fund specified research at Signal for one year. For each kinase target,
Signal will have the sole option at a specified stage prior to human clinical
trials and again at a specified stage during human clinical trials to negotiate
a worldwide joint development agreement with Pliva which would reflect equal
sharing by the parties of both revenue and expenses associated with development
and commercialization of a licensed product arising from the collaboration. If
Signal elects not to exercise either of these options, Pliva will be obligated
to pay Signal royalties on net sales of licensed products. Either party may
terminate this agreement upon the bankruptcy, insolvency, dissolution or winding
up of the other party, or in the event a material breach by the other party
remains uncured for 60 days.


LICENSE AGREEMENTS

Signal has established a number of license agreements with academic
institutions. Signal's principal license agreements are:


THE REGENTS OF THE UNIVERSITY OF CALIFORNIA

In October 1993, Signal entered into a license agreement with The Regents of the
University of California, as amended in June 1997 and February 1998, under which
Signal obtained a worldwide exclusive license for the JNK gene regulating enzyme
based on the research of Dr. Michael Karin, one of Signal's scientific founders
and advisors. The license also covers methods for the production and screening
of nerve cells. In February 1998, Signal also secured from The Regents exclusive
worldwide license rights to certain patents filed by Dr. Karin relating to
specified NF-kB signaling molecules, IKK1 and IKK2. Under the license agreement,
Signal paid initial license fees and extension payments and issued shares of
Signal's common stock to The Regents, and is obligated to make specified royalty
and milestone payments. The term of the license remains in effect for the life
of the last-to-expire patent covered under each agreement.


THE UNIVERSITY OF MASSACHUSETTS

In October 1996 and 1997, Signal entered into worldwide exclusive license
agreements with the University of Massachusetts. Under the license agreements,
Signal has exclusive rights under patent applications and nonexclusive worldwide
rights under unpatented know-how to develop drugs targeting JNK and three
intracellular gene regulating proteins in the p38 pathway, MKK3, MKK4 and MKK6,
based on the research of Dr. Roger J. Davis, one of Signal's scientific
advisors. Upon entering into both of the license agreements, Signal paid a
license fee and issued shares of Signal's common stock to the University of
Massachusetts and is obligated to make royalty and milestone payments. The term
of the licenses remains in effect for the longer of 10 years or the life of the
last-to-expire patent under the agreements.


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PATENTS AND PROPRIETARY RIGHTS

Signal will be able to protect its proprietary rights from unauthorized use by
third parties only to the extent that its proprietary rights are covered by
valid and enforceable patents or are effectively maintained as trade secrets.
Accordingly, Signal seeks patent protection for its proprietary technology,
targets and potential products. As of June 30, 2000, Signal owned or had
licensed 29 issued United States patents, 2 notices of allowance from the United
States Patent and Trademark Office, 9 corresponding issued foreign patents and
35 pending United States patent applications. In addition, as of that date,
Signal owned or had licensed 7 corresponding international filings under the
Patent Cooperation Treaty and 43 pending foreign national patent applications.

Signal's policy is to file patent applications and to protect technology,
inventions and improvements to inventions that are commercially important to the
development of Signal's business. Signal seeks United States and international
patent protection for the molecular targets it discovers, as well as therapeutic
products and processes, drug discovery technologies and other inventions.
Signal's commercial success will depend in part on obtaining this patent
protection. Signal also intends to seek patent protection or rely upon trade
secret rights to protect other technologies that may be used to discover and
characterize molecular targets and that may be used to develop novel drugs.
Signal seeks protection, in part, through confidentiality and proprietary
information agreements.

Signal has developed proprietary technology for use in molecular target
discovery, regulatory pathway identification and assay design and, in addition
to Signal's issued patents, has filed a number of patent applications in these
areas. Also, an increasing percentage of Signal's recent patent applications
have been related to potential product candidates, or compounds, that it has
discovered.

Signal is aware of three issued United States patents relating to specific
methods for regulating gene expression. Signal believes that it has not
infringed, and is not currently infringing, the claims of the patents.
Nonetheless, Signal may in the future have to prove it is not infringing these
patents or be required to obtain licenses to one or more of these patents, and
Signal does not know whether such licenses will be available on commercially
reasonable terms, or at all. Signal is also aware of a United States patent
which has issued to a third party claiming subject matter relating to the NF-kB
pathway which appears to overlap with technology claimed in some of Signal's
pending NF-kB patent applications. Signal believes that one or more interference
proceedings will be initiated by the U.S. Patent and Trademark Office to
determine priority of invention for this subject matter. While Signal cannot
predict the outcome of any such proceedings, in the event Signal does not
prevail Signal believes it can use alternative methods for its NF-kB drug
discovery program for which it has issued United States patents that are not
claimed by the subject matter of the third party patents.


COMPETITION

Signal faces, and will continue to face, intense competition from pharmaceutical
and biotechnology companies and other commercial enterprises, as well as
numerous academic and research institutions and governmental agencies. Other
companies are pursuing the same and similar technologies, including the
discovery of targets that regulate genes. Many of Signal's competitors and
potential competitors have substantially greater advantages in the areas of
capital resources, research and development resources, manufacturing, sales and
marketing, and production facilities. Additionally, many of Signal's competitors
have significantly greater experience than it does in undertaking target and
drug discovery, preclinical product development, testing and clinical trials of
potential pharmaceutical products, and obtaining FDA and other regulatory
clearances.

Smaller companies also may prove to be significant competitors, particularly
through proprietary research discoveries and collaborative arrangements with
large pharmaceutical and established biotechnology companies. Many of Signal's
competitors have significant products that have been approved or are in
development and operate large, well-funded research and development programs.
Signal also faces competition from academic institutions, governmental agencies
and other public and private research organizations in developing drugs and in
recruiting and retaining highly qualified scientific and management personnel.
Signal's competitors, either alone or with their collaborative


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partners, may succeed in developing technologies or drugs that are more
effective, safer, more affordable or more easily administered and may achieve
patent protection or commercialize drugs sooner than Signal. Developments by
others may render Signal's product candidates or Signal's technologies obsolete.


GOVERNMENT REGULATION

The manufacturing and marketing of Signal's potential products and ongoing
research and development activities are subject to extensive regulation by
numerous governmental authorities in the United States and other countries.
Before marketing in the United States, any drug developed by Signal must undergo
rigorous preclinical testing and clinical trials and an extensive regulatory
clearance process implemented by the FDA under the federal Food, Drug, and
Cosmetic Act. The FDA regulates, among other things, the development, testing,
manufacture, safety, efficacy, record keeping, labeling, storage, clearance,
advertising, promotion, sale and distribution of biopharmaceutical products.
None of Signal's product candidates has received marketing clearance in the
United States or any foreign market. The regulatory review and clearance
process, which includes preclinical testing and clinical trials of each product
candidate, is lengthy, expensive and uncertain. Securing FDA clearance requires
the submission of extensive preclinical and clinical data and supporting
information to the FDA for each indication to establish a product candidate's
safety and efficacy. The process takes many years, requires the expenditure of
substantial resources, involves post-marketing surveillance, and may involve
ongoing requirements for post-marketing studies. Before commencing clinical
investigations in humans, Signal must submit to, and receive clearance from, the
FDA of an Investigational New Drug application. Signal expects to rely on some
of its corporate collaborators to file INDs and generally direct the regulatory
review process for some of Signal's products.

Outside the United States, Signal's ability to market a product is contingent
upon receiving a marketing authorization from the appropriate regulatory
authorities. The requirements governing the conduct of clinical trials,
marketing authorization, pricing and reimbursement vary widely from country to
country. At present, foreign marketing authorizations are applied for at a
national level, although within the European Union registration procedures are
available to companies wishing to market a product in more than one European
Union member state. If the regulatory authority is satisfied that adequate
evidence of safety, quality and efficacy has been presented, a marketing
authorization will be granted. This foreign regulatory approval process involves
all of the risks associated with FDA clearance discussed above.


MANUFACTURING

To date, Signal has not manufactured any products for preclinical, clinical or
commercial purposes and does not have any manufacturing facilities. Signal
intends to use third-party contract manufacturers or its corporate collaborators
for the production of material for use in preclinical and clinical trials and
for the manufacture of future products for commercialization. Signal cannot
assure you that it or any outside manufacturers can produce potential products
of suitable quality in sufficient quantity in a cost-effective manner, if at
all.

Signal and its contract manufacturers also are required to comply with the
applicable FDA and other applicable domestic and foreign regulatory authorities'
current good manufacturing practice regulations. Signal or its contract
manufacturers may not be able to comply with the applicable good manufacturing
practice requirements and other FDA or other applicable domestic and foreign
regulatory requirements.


OTHER THIRD PARTY SERVICES

In addition to manufacturing arrangements with third parties, Signal has also
contracted with third parties for the performance of preclinical studies,
including studies regarding the biological activity, safety, absorption,
metabolism and elimination of Signal's drug candidates, and Signal expects to


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<PAGE>

continue to contract with third parties for these and similar services. Signal
also expects that it will contract with third parties to conduct all clinical
trials, if any, of its drug candidates. There are multiple companies capable of
performing these services, and, accordingly, Signal does not expect to be
dependent on any single company for these services.


EMPLOYEES


As of June 30, 2000, Signal had 93 full-time employees, including 42 with Ph.D.
degrees. Of Signal's workforce, 75 employees are engaged in research and
development and 18 are engaged in business development, finance and
administration. Signal has assembled a group of experienced scientists and
managers skilled in each phase of target and drug discovery. Signal also retains
outside consultants. None of Signal's employees is covered by collective
bargaining arrangements, and Signal's management considers its relationships
with its employees to be good.


FACILITIES


Signal currently leases 25,000 square feet of laboratory and office space at
5555 Oberlin Drive, San Diego, California. Signal's lease for this facility
expires on January 31, 2001, with an option to renew for two additional periods
of three years each. Signal also leases 11,000 square feet of laboratory and
office space at 5626 Oberlin Drive and 9,500 square feet of office space at 5627
Oberlin Drive, San Diego, California. Signal's leases for these facilities
expire on December 31, 2003. Signal believes that its existing facilities are
adequate to meet its business requirements for the near-term and that additional
space will be available on commercially reasonable terms, if required.


LEGAL PROCEEDINGS


Signal is not a party to any legal proceedings at this time.



                                   MANAGEMENT


EXECUTIVE OFFICERS


     Alan J. Lewis, Ph.D., age 54, has served as Signal's chief executive
officer and as a director of Signal since 1996 and as Signal's president since
1994. Prior to joining Signal, Dr. Lewis worked for 15 years at the Wyeth-Ayerst
Research Division of American Home Products Corporation, a pharmaceutical
company, where he served as vice president of research from 1990 to 1994. At
Wyeth-Ayerst, Dr. Lewis was responsible for drug discovery efforts in CNS,
cardiovascular, inflammatory, allergy and bone metabolism diseases. Dr. Lewis
currently serves as a director of Allergan Specialty Therapeutics, Inc., a
pharmaceutical company. He holds a Ph.D. in Pharmacology from the University of
Wales in Cardiff and completed his post-doctoral training at Yale University.


EXECUTIVE COMPENSATION


     Signal entered into an employment letter agreement with Alan J. Lewis,
dated December 8, 1993, providing for an annual salary, subject to adjustment
from time to time, a signing bonus of $50,000, additional bonuses and options
subject to specified performance milestones, assistance with home financing, and
an opportunity to acquire 450,000 shares of Signal common stock under Signal's
stock option plan. The term of the employment letter agreement was for one year,
renewable annually. During 1999 Alan J. Lewis received a salary in the amount of
$300,000 and a bonus in the amount of $54,000.


     Alan J. Lewis was not granted any options during the fiscal year ended
December 31, 1999.

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<PAGE>

The following table sets forth summary information regarding the number and
value of options exercised by Dr. Lewis during 1999 and held by him as of
December 31, 1999.


             AGGREGATED 1999 OPTION EXERCISES AND YEAR-END VALUES

<TABLE>
<CAPTION>
                                                    NUMBER OF SECURITIES              VALUE OF UNEXERCISED
                                                   UNDERLYING UNEXERCISED             IN-THE-MONEY OPTIONS
                                                     OPTIONS AT YEAR END                 AT YEAR-END(1)
                                               -------------------------------   ------------------------------
                      SHARES
                   ACQUIRED ON       VALUE
      NAME           EXERCISE      REALIZED     EXERCISABLE     UNEXERCISABLE     EXERCISABLE     UNEXERCISABLE
---------------   -------------   ----------   -------------   ---------------   -------------   --------------
<S>               <C>             <C>          <C>             <C>               <C>             <C>
Alan J. Lewis          --            $ --         75,000             --             $16,500            --
</TABLE>

(1)  The values of unexercised in-the-money options at year-end in the table
     above were determined using the fair market value of the securities
     underlying the option as of December 31, 1999 ($0.50 per share) minus the
     per share exercise price multiplied by the number of shares.

Dr. Lewis' stock options are immediately exercisable for shares of restricted
common stock and are subject to a right of repurchase under a vesting schedule.
As of December 31, 1999 Dr. Lewis held 79,064 shares and 39,064 exercisable
options remaining subject to a vesting schedule.


CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

In June 1994, Signal loaned $250,000 to Alan J. Lewis to assist with the
purchase of a residence in connection with Dr. Lewis' relocation to San Diego,
California. Under the terms of a Promissory Note dated June 14, 1994, as amended
on May 14, 1998 and October 27, 1999, the principal amount of the loan plus
accrued interest shall be amortized over a period of five years following June
14, 2002, with monthly payments commencing in July 2002. The principal amount of
the loan will be interest-free for eight years from the date of the Promissory
Note, and thereafter will accrue interest at the per annum rate of 7.52%,
compounded annually. Interest will also begin to accrue at the same rate in the
event that Dr. Lewis' employment is terminated for any reason. The parties also
entered into a security agreement on the same date whereby Dr. Lewis pledged all
present and future shares of our common stock held by him (plus all cash and
stock dividends attributable to such shares) as security for the loan. As of
July 13, 2000, the total amount outstanding under this loan was $250,000.

In May 1998, Signal loaned $62,000 to Alan J. Lewis in connection with the
exercise of options to purchase 425,000 shares of our common stock. Under the
terms of the promissory note, dated May 8, 1998, the principal amount of the
loan plus accrued interest at a per annum rate equal to 5.69%, compounded
annually, shall be due and payable five years from the date of the loan. Under a
stock pledge agreement entered into on the same date, Dr. Lewis pledged all
present and future shares of our common stock held by him, plus all cash and
stock dividends attributable to such shares, as security for the loan. As of
July 13, 2000, the total amount outstanding under this loan was $62,000.


                        PRINICIPAL STOCKHOLDERS OF SIGNAL

The following table sets forth information regarding the beneficial ownership of
common stock and preferred stock of Signal as of July 13, 2000 by:

o  each person who is known by Signal to own beneficially more than five percent
   of its common stock or preferred stock;

o  each of the current directors, chief executive officer and other executive
   officers of Signal who earned more than $100,000 during 1999; and

o  all directors and executive officers of Signal as a group.

Beneficial ownership is determined in accordance with the rules of the
Securities and Exchange Commission and generally includes voting or investment
power with respect to securities. Except as indicated by footnote, and subject
to community property laws where applicable, the shareholders


                                       78
<PAGE>

named in the table below have sole voting and investment power with respect to
all shares of common stock and preferred stock shown as beneficially owned by
them. Perentage ownership of common stock is based on 4,952,264 shares of common
stock outstanding as of July 13, 2000, together with applicable options and
warrants for each shareholder, and percentage ownership of preferred stock is
based on 24,492,639 shares of preferred stock outstanding as of July 13, 2000.

<TABLE>
<CAPTION>
                                                      SHARES
                                                   ISUABLE UPON
                                                    EXERCISE OF
                                       COMMON      OPTIONS THAT    PERCENTAGE OF                         PERCENTAGE OF
                                       STOCK      VEST WITHIN 60    COMMON STOCK                        PREFERRED STOCK
                                    BENEFICIALY    DAYS OF JULY     BENEFICIALLY     PREFERRED STOCK     BENEFICIALLY
     NAME OF BENEFICIAL OWNER          OWNED         13, 2000          OWNED       BENEFICIALLY OWNED        OWNED
---------------------------------- ------------- ---------------- --------------- -------------------- ----------------
<S>                                <C>           <C>              <C>             <C>                  <C>
Serono S.A.                                 --             --              *            3,708,815             15.1%
 15bis Chemin des Mines
 1202 Geneva, Switzerland
Patrick F. Latterell(1)                150,000             --            3.0%           2,822,142             11.5
 Venrock Associates
 30 Rockefeller Plaza,
 Room 5508
 New York, New York 10112
Accel Partners(2)                      135,416             --            2.7            2,832,666             11.6
 428 University Avenue
 Palo Alto, California 94301
Kleiner Perkins Caufield & Byers        33,332             --              *            2,832,670             11.6
 2750 Sand Hill Road
 Menlo Park, California 94025
Arnold Oronsky, Ph.D.(3)                41,666         41,666              *            2,222,163              9.1
 InterWest Partners
 3000 Sand Hill Road, Bldg. 3,
 Suite 255
 Menlo Park, California 94025
Lombard Oldier & Cie                        --             --              *            1,570,681              6.4
 11, rue de la Corraterie 1204
 Geneva, Switzerland
Oxford Bioscience Partners(4)               --             --              *            1,481,442              6.0
 650 Town Center Drive,
 Suite 180
 Costa Mesa, California 92626
U.S. Venture Partners(5)                    --             --              *             1,481.442             6.0
 2180 Sand Hill Road,
 Suite 300
 Menlo Park, California 94025
Alan J. Lewis, Ph.D.                   680,937          5,937           13.7                   --                *
Harry F. Hixson, Ph.D.(6)               71,666         41,666            1.4              319,520              1.3
David W. Anderson, Ph.D.               293,666         93,666            5.8                   --                *
Bradley B. Gordon                      280,000             --            5.7                   --                *
John P. Walker(7)                      150,000             --            3.0                   --                *
Douglas E. Richards                    275,000        275,000            5.3                   --                *
All directors and executive          1,942,935        457,935           35.9            5,363,825             21.9
 officers as a group (8 persons)
</TABLE>

* Less than one percent (%)

----------
(1)  Includes 77,556 shares of common stock and 1,920,853 shares of preferred
     stock held by Venrock Associates and 34,944 shares of common stock and
     901,289 shares of preferred stock held by


                                       79
<PAGE>

    Venrock Associates II, L.P., entities for which Mr. Latterell is a general
    partner. Mr. Latterell disclaims benefical ownership of all such shares,
    except to the extent of his pecuniary or pro rata interest in such shares.

(2)  Includes the following shares held by the following affiliated entities: o
     119,116 shares of common stock and 2,370,945 shares of preferred stock held
     by Accel IV L.P.; o3,700 shares of common stock and 104,807 shares of
     preferred stock held by Accel Investors '93 L.P.; o 1,800 shares of common
     stock and 50,988 shares of preferred stock held by Accel Keiretsu L.P.; o
     8,000 shares of common stock and 226,614 shares of preferred stock held by
     Accel Japan L.P.; o 2,200 shares of common stock and 62,317 shares of
     preferred stock held by Ellmore C. Patterson Partners; and o600 shares of
     common stock and 16,995 shares of preferred stock held by Prosper Partners.

(3)  Includes 2,208,274 shares held by InterWest Partners V and 13,889 shares
     held by InterWest Investors V, which are affiliated entities. Dr. Oronsky
     is a general partner of InterWest Partners V. Dr. Oronsky disclaims
     beneficial ownership of all such shares, except to the extent of his
     pecuniary or pro rata interest in such shares.

(4)  Includes the following shares held by the following affiliated entities:

     o 927,772 shares held by Oxford Bioscience Partnters L.P.;
     o 296,289 shares held by Oxford Bioscience Partners (Adjunct) L.P.; and
     o 257,381 shares held by Oxford Bioscience Partners (Bermuda) Limited
       Partnership.

(5)  Includes:
     o 1,281,448 shares held by U.S. Venture Partners IV, L.P.;
     o 155,551 shares held by Second Ventures II, L.P.; and
     o 44,443 shares held by USVP Entrepreneur Partners II, L.P.

(6)  Includes 319,520 shares held by the Harry F. Hixson, Jr. Separate Property
     Trust Dated December 15, 1995 , of which Dr. Hixson is the sole trustee.

(7)  Includes 150,000 shares held by the Walker Living Trust Dated March 3,
     1995, of which Mr. Walker is the sole trustee.


                                       80
<PAGE>

                    MANAGEMENT'S DISCUSSION AND ANALYSIS OF
                 FINANCIAL CONDITION AND RESULTS OF OPERATIONS


OVERVIEW

Signal was incorporated in July 1992 and has devoted substantially all of its
resources since that time to research and development directed toward the
discovery of proprietary drug targets and novel small molecule drugs that
regulate genes associated with disease. Through both internally funded programs
and in conjunction with Signal's corporate collaborators, Signal is working to
identify gene regulating drug targets and potential drug products for treating
cancer, inflammatory disease, bone metabolic disease, cardiovascular disease,
neurological disease and viral infections. Signal has incurred significant
losses since inception, with an accumulated deficit of approximately $41.3
million as of March 31, 2000, due primarily to ongoing expenditures related to
its internally funded research and development programs. Signal expects to
continue to incur substantial expenditures and operating losses for at least the
next several years as Signal continues its target and drug discovery and
preclinical drug development efforts and retains its research and development
programs for longer periods of time prior to licensing rights to corporate
collaborations. Such activities will result in substantial research and
development expenses, general and administrative expenses and related capital
expenditures. Signal's results of operations have fluctuated from period to
period and likely will continue to fluctuate substantially in the future based
upon the timing, duration and composition of funding under various collaborative
agreements, the initiation, expansion and termination of research and
development programs, the acquisition of technologies, compound libraries and
product rights, as well as the progress of our research and development
programs. Results of operations for any period may be unrelated to results of
operations for any other period. In addition, historical results should not be
viewed as indicative of future operating results.

A key element of Signal's strategy is to enter into collaborations with
pharmaceutical and biotechnology companies in order to enhance and accelerate
its target and drug discovery programs and to fund its capital requirements.
Signal's principal sources of revenue for the next several years are expected to
consist of license fees and upfront payments, research and development funding
and milestone payments under such collaborations, government grants, if any, and
interest income. To date, Signal's revenue has been due primarily to
arrangements with the following collaborators: Tanabe, which was entered into in
March 1996 and concluded in March 1998; Organon, which was entered into in July
1996 and concluded in August 1999; Roche Bioscience, which was entered into in
August 1996 and concluded in August 1999; Serono, which was entered into in
November 1997; DuPont Pharmaceuticals, which was entered into in December 1997;
Nippon Kayaku, which was entered into in February 1998 and concluded in July
2000; Axys Pharmaceuticals, which was entered into in October 1999; Byk Gulden,
which was entered into in June 2000; and Pliva, which was entered into in July
2000.

Under Signal's collaborative arrangements, Signal has received payments of
approximately $56.4 million to date in license fees, research and development
payments and equity investments, of which approximately $39.8 million has been
recognized as revenue. To date, Signal has received an equity milestone of $1.0
million and license fees, upfront payments and research and development payments
of approximately $43.3 million. In 1997, Signal recognized aggregate revenue of
$725,000 in license fees and upfront payments, $6.6 million in research and
development payments from our collaborators and $264,000 in government grants.
In 1998, we recognized aggregate revenue of $3.1 million in license fees and
upfront payments, $11.9 million in research and development payments from our
collaborators and $387,000 in government grants. In 1999, we recognized
aggregate revenue of $1.9 million in license fees and upfront payments, $9.4
million in research and development payments from our collaborators and $528,000
in government grants.


RESULTS OF OPERATIONS


COMPARISON OF THREE MONTHS ENDED MARCH 31, 2000 AND 1999

Revenue. Revenue for the three months ended March 31, 2000 decreased to $2.7
million from $2.9 million for the three months ended March 31, 1999. The
decrease was due primarily to the conclusion


                                       81
<PAGE>

of certain collaborative agreements resulting in decreased revenue of $1.1
million. Such decrease was partially offset by an amendment to the collaborative
and license agreement with Serono and the initiation of a new collaboration
agreement with Axys resulting in additional research and development revenue of
$300,000 and $625,000, respectively.


Research and Development Expenses. Signal's research and development expenses
for the three months ended March 31, 2000 increased to $5.2 million from $4.3
million for the three months ended March 31, 1999. The increase was due
primarily to increases in product development costs of $481,000 and deferred
compensation expense of $414,000.


General  and  Administrative  Expenses.   Signal's  general  and  administrative
expenses  for the three  months  ended March 31, 2000  increased to $1.0 million
from  $809,000 on March 31, 1999.  The  increase was due  primarily to increased
salary  expense  of  $106,000,   resulting  from  incentive  bonuses  and  merit
increases, and increased deferred compensation expense of $70,000.

In June 2000, Signal expensed all of the accumulated costs related to its Form
S-1 Registration Statement filed with the Securities and Exchange Commission in
February 2000, of which $543,000 were included in other current assets at March
31, 2000.


Interest Income (Expense), Net. Net interest income for the three months ended
March 31, 2000 increased to $53,000 from $18,000 for the three months ended
March 31, 1999. The increase in net interest income was due primarily to
decreased interest expense on lower capital lease and note obligation balances.


COMPARISON OF YEARS ENDED DECEMBER 31, 1999, 1998 AND 1997


Revenue. Revenue for the year ended December 31, 1999 decreased to $11.7 million
from $15.4 million for the year ended December 31, 1998. The decrease was due
primarily to the termination of the Tanabe agreement in 1998 that resulted in
decreased revenues of $4.1 million. Revenue for the year ended December 31, 1998
increased to $15.4 million from $7.6 million for the year ended December 31,
1997. The increase was due primarily to additional collaborative agreements that
were in place during 1998 and an amendment to the collaborative agreement with
Tanabe which events resulted in recognition of additional research and
development revenue of $6.4 million and $840,000, respectively.


Research and Development Expenses. Signal's research and development expenses
for the year ended December 31, 1999 increased to $16.7 million from $15.6
million for the year ended December 31, 1998. The increase in 1999 was due
primarily to increased salary and relocation expense of $857,000, resulting from
the hiring of additional research and development personnel and increased
product development expense of $576,000. Research and development expenses for
the year ended December 31, 1997 increased to $15.6 million from $10.3 million
for the year ended December 31, 1997. The increase was due primarily to
increased expenses for salaries and relocation of $1.7 million resulting from
the hiring of additional research and development personnel, the purchase of
laboratory materials of $1.2 million for expansion of our research programs,
facilities expansion expenses of $506,000, depreciation expense of $500,000,
amortization of deferred compensation of $376,000, increased travel expenses of
$198,000 and the initiation of additional academic research collaborations of
$184,000.


General and Administrative Expenses. Signal's general and administrative
expenses for the year ended December 31, 1999 decreased to $3.0 million from
$4.8 million in 1998. The decrease was due primarily to reductions in fees for
professional services of $1.0 million, equipment rentals of $245,000 and salary
expense of $185,000 due to lower general and administrative headcount. Signal's
general and administrative expenses for the year ended December 31, 1998
increased to $4.8 million from $2.8 million for the year ended December 31,
1997. The increase was due primarily to increased fees for professional services
of $827,000, and increased salary expense of $591,000 resulting from the hiring
of additional personnel, amortization of deferred compensation of $231,000 and
facilities expansion of $160,000.


                                       82
<PAGE>

Interest Income (Expense), Net. Net interest income (expense) for the years
ended December 31, 1999, 1998 and 1997 was $155,000, $600,000 and ($191,000),
respectively. The decrease in net interest income in 1999 form 1998 was due
primarily to lower average cash balances. The increase in net interest income in
1998 from 1997 was due primarily to higher average cash balances.

Imputed Dividend. Due to Signal's achievement of a certain milestone in 1999,
DuPont Pharmaceuticals purchased 288,708 shares of Signal's Series F-1 Preferred
Stock for total cash proceeds of $1.0 million. Signal recognized an imputed
dividend of $818,487 to reflect a beneficial conversion feature on these
preferred shares.

Income Taxes. At December 31, 1999, Signal, had federal and state net operating
loss carryforwards of approximately $30.6 million and $11.7 million,
respectively. The federal tax loss carryforwards will begin expiring in 2007,
unless previously used, and the state tax loss carryforwards will begin expiring
in 1998. Signal has provided a 100% valuation allowance against the related
deferred tax assets because realization of such tax benefits is not assured.
Future use of these carryforwards may be limited in any one fiscal year under
the Internal Revenue Code and similar state provisions; however, the annual
limitation will not prevent the entire amount of the carryforwards from being
used during the carryforward period. Therefore, Signal does not believe any such
limitation will have a material effect upon the use of these carryforwards.

LIQUIDITY AND CAPITAL RESOURCES

Since inception, Signal has funded its operations primarily through private
placements of preferred stock, funds provided under the Tanabe, Organon, Roche
Bioscience, Serono, DuPont Pharmaceuticals, Nippon Kayaku and Axys
Pharmaceuticals collaborative agreements, and, to a lesser extent, through debt
and equipment financing, interest income and government research grant revenue.
As of March 31, 2000, Signal had received $43.6 million in net proceeds from the
sales of equity securities, $43.3 million under its collaborative agreements,
$7.0 million in debt and equipment financing, $3.0 million in interest income
and $1.9 million in research grants from the NIH. As of March 31, 2000, Signal
had approximately $6.3 million in cash, cash equivalents and short-term
investments.

Net cash used in operations for the three months ended March 31, 2000 was $2.7
million, compared to $111,000 for the three months ended March 31, 1999. Net
cash used in operations increased for the three months ended March 31, 2000 over
the three months ended March 31, 1999 due primarily to internally funded
research programs, an increase in product development expenses and costs related
to the Registration Statement on Form S-1 filed by Signal during the first
quarter of 2000.

As of March 31, 2000,  Signal had  purchased  with cash $5.3 million in property
and  equipment,  primarily for facility  improvements  and laboratory and office
equipment.  Signal has  financed  approximately  $4.9  million of our  equipment
through capital leases and equipment note obligations.

Signal believes its existing capital resources, committed revenue from our
existing collaborations, committed debt financing under existing loan agreements
and interest income should be sufficient to fund its anticipated operating
expenses and capital requirements at least through the end of the year 2000.
Signal's future funding requirements include continued and increased
expenditures for research and development activities, as well as expenditures
related to facility improvements, the purchase of additional laboratory and
office equipment, the purchase of technology, compound libraries and product
rights, the repayment of debt, working capital and general corporate purposes.
Signal cannot assure you that changes in its research and development plans and
collaborations, the acquisition of additional technology, compound libraries and
product rights or other changes affecting its operating expenses or use of
capital will not result in the expenditure of available resources before such
time. The costs associated with the clinical development of new drugs are
substantial and generally increase over time. If Signal is successful in
advancing one or more drug candidates into clinical development, its need for
additional capital will increase substantially.

In any event, Signal will need to raise substantial additional capital to fund
its operations in future periods. Signal intends to seek additional funding
through collaborative arrangements, public or private equity or debt financing,
property and equipment financing or other financing sources that


                                       83
<PAGE>

may be available. If additional funds are raised through the sale of equity
securities, substantial dilution to Signal may result. Debt financing, if
available, may involve restrictive covenants. Further, Signal cannot assure you
that additional financing will be available on acceptable terms, if at all. If
adequate funds are not available, Signal may be required to delay, or reduce the
scope of, or eliminate one or more of our research and development programs or
to obtain funds through strategic collaborations that are on unfavorable terms
or that may require us to relinquish rights to some of our technologies, product
candidates, products or marketing territories that we would otherwise seek to
retain. Signal's failure to raise capital when needed could have a material
adverse effect on its business, financial condition and results of operations.


NEW ACCOUNTING PRONOUNCEMENTS.

Signal expects to adopt SFAS No. 133, Accounting for Derivative Instruments and
Hedging Activities, effective January 1, 2001. SFAS No. 133 will require Signal
to recognize all derivatives on the balance sheet at fair value. Signal does not
anticipate that the adoption of the SFAS No. 133 will have a significant effect
on its results of operations or financial positions.


QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

We invest excess cash primarily in U.S. government securities and marketable
debt securities of financial institutions and corporations with strong credit
ratings. These instruments have maturities of three months or less when
acquired. We do not utilize derivative financial instruments, derivative
commodity instruments or other market risk sensitive instruments, positions or
transactions in any material fashion. Accordingly, we believe that, while the
instruments we hold are subject to changes in the financial standing of the
issuer of such securities, we are not subject to any material risks arising from
changes in interest rates, foreign currency exchange rates, commodity prices,
equity prices or other market changes that affect market risk sensitive
instruments.


RECENT DEVELOPMENT

In June 2000, Signal entered into a secured line of credit for up to $5,000,000
that can be borrowed against through December 31, 2000, as needed. The proceeds
of any borrowings under the line of credit will be used for general corporate
purposes and working capital. The interest rate will float with the Treasury
rate as the proceeds are drawn down and then be fixed for the term, maintaining
the spread. Borrowings under the line of credit are payable in either twelve or
thirty-six monthly installments, at Signal's option, and are secured by the
assets of Signal. To date, Signal has not drawn down any proceeds from the line
of credit. In conjunction with the line of credit, Signal issued the creditor a
warrant to purchase up to 225,000 shares of Series C-2 Preferred Stock at a
price of $4.00 per share, of which 150,000 shares were issuable under the
warrant upon Signal's signing of a loan commitment letter in May 2000, and the
remaining 75,000 shares become issuable under the warrant upon any additional
borrowing against the line of credit greater than $2.5 million. The warrant
expires ten years from the date of grant.

In June 2000, Signal entered into a collaborative agreement with Byk Gulden
focused on the discovery and optimization of inhibitors of an unspecified kinase
target being investigated by Byk Gulden. Under the terms of the agreement,
Signal will be responsible for constructing a molecular model of the kinase
target and for screening its proprietary kinase inhibitor library to identify
small molecule inhibitors of this drug target. Byk Gulden is obligated to pay
Signal a license fee of $250,000 and has agreed to fund specified research as
part of this effort for three months and can extend research funding under the
agreement for an additional nine-month period. To date, Signal has received
$312,000 in research and development funding from Byk Gulden. If Byk Gulden
extends the research funding, Signal will be responsible for optimizing
screening hits using medicinal chemistry to generate lead compounds. Byk Gulden
also will make preclinical, clinical and commercialization milestone payments
for compounds licensed by Byk Gulden which arise from the collaboration. In
addition, Signal will retain the right to modify any compound discovered or
generated by the collaboration to identify inhibitors of other targets


                                       84
<PAGE>

in the same kinase family, and such inhibitors will be owned exclusively by
Signal. Either party may terminate this agreement upon the bankruptcy,
insolvency, dissolution or winding up of the other party, or in the event a
material breach by the other party remains uncured for sixty days.

In July 2000, Signal entered into a collaborative agreement with Pliva focused
on the discovery and optimization of inhibitors of two unspecified kinase
targets being investigated by Pliva. Under terms of the agreement, Signal will
be responsible for screening its proprietary kinase inhibitor library, and
potentially its diversity library, to identify small molecule inhibitors of each
of these two drug targets. Pliva will pay Signal a license fee and payments
based on the achievement of specified research and development milestones. In
addition, if specified research milestones are achieved, Pliva will fund
specified research at Signal. For each kinase target, Signal will have the sole
option at a specified stage prior to the start of human clinical trials and
again at a specified state during human clinical trials to negotiate a worldwide
joint development agreement which shall reflect equal sharing by the parties of
both revenue and expenses associated with development and commercialization of a
licensed product arising from the collaboration. If Signal elects not to
exercise either of these options, Pliva will be obligated to pay Signal a
royalty on net sales of licensed products. Either party may terminate the
collaboration agreement upon the bankruptcy, insolvency, dissolution or winding
up of the other party, or in the event a material breach by the other party
remains uncured for sixty days.


            MARKET PRICE OF AND DIVIDENDS ON SIGNAL'S COMMON EQUITY
                         AND RELATED SHAREHOLDER MATTERS

There is no established public trading market for Signal's capital stock.

Signal has never declared or paid cash dividends on its capital stock. Signal
expects to retain future earnings, if any, for the development of its business
and does not anticipate paying any cash dividends in the foreseeable future. In
addition, the terms of its secured line of credit from MMC/GATX Partnership No.
1 prohibit Signal from paying any dividends and making any distributions and
limit Signal's ability to repurchase stock.


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                      DESCRIPTION OF CELGENE CAPITAL STOCK

As of July 13, 2000, Celgene's authorized capital stock consists of 120,000,000
shares of common stock, par value $.01 per share, and 5,000,000 shares of
preferred stock, par value $.01 per share, of which 520 shares have been
designated Series A convertible preferred stock and 20,000 shares have been
designated as Series B convertible preferred stock. As of July 13, 2000, there
were 66,526,483 shares of common stock outstanding, no shares of Series A
convertible preferred stock outstanding and no shares of Series B convertible
preferred stock outstanding.


COMMON STOCK

Holders of Celgene common stock are entitled to one vote for each share held on
all matters submitted to a vote of stockholders, and do not have cumulative
voting rights. Holders of common stock are entitled to receive ratably such
dividends, if any, as may be declared by Celgene's board of directors out of
funds legally available therefor, and subject to any preferential dividend
rights of any then outstanding preferred stock. Upon liquidation, dissolution,
or winding up of Celgene, the holders of common stock are entitled to receive
ratably Celgene's net assets available after the payment of all debts and other
liabilities and subject to any liquidation preference of any then outstanding
preferred stock. Holders of common stock have no preemptive, subscription or
conversion rights. There are no redemption or sinking fund provisions applicable
to the common stock. The outstanding shares of common stock are, and the shares
issued by Celgene in the merger will be when issued and paid for, fully paid and
non-assessable.


PREFERRED STOCK

Celgene's board of directors has the authority, subject to certain restrictions,
without further stockholder approval, to issue, at any time and from time to
time, shares of preferred stock in one or more series. Each such series shall
have such number of shares, designations, preferences, voting powers,
qualifications, and special or relative rights or privileges as shall be
determined by our board of directors, which may include, among others, dividend
rights, voting rights, redemption and sinking fund provisions, liquidation
preferences, conversion rights and preemptive rights, to the full extent now or
hereafter permitted by the laws of the State of Delaware.

The rights of the holders of common stock will be subject to, and may be
adversely affected by, the rights of holders of any preferred stock that may be
issued in the future. Such rights may include voting and conversion rights which
could adversely affect the holders of the common stock. Satisfaction of any
dividend preferences of outstanding preferred stock would reduce the amount of
funds available, if any, for the payment of dividends on common stock. Holders
of preferred stock would typically be entitled to receive a preference payment.


SHAREHOLDER RIGHTS PLAN

Celgene's board of directors has adopted a shareholder rights plan. The
shareholder rights plan was adopted to give Celgene's board of directors
increased power to negotiate in Celgene's best interests and to discourage
appropriation of control of Celgene at a price that is unfair to its
stockholders. It is not intended to prevent fair offers for acquisition of
control determined by our board of directors to be in the best interests of
Celgene and its stockholders, nor is it intended to prevent a person or group
from obtaining representation on or control of Celgene's board of directors
through a proxy contest, or to relieve Celgene's board of directors of its
fiduciary duty to consider any proposal for its acquisition in good faith.

The shareholder rights plan involved the distribution of one "right" as a
dividend on each outstanding share of Celgene common stock to all holders of
record on September 26, 1996. Each right shall entitle the holder to purchase
one-tenth of a share of common stock. The rights trade in tandem with the common
stock until, and become exercisable upon, the occurrence of certain triggering
events, and the exercise price is based on the estimated long-term value of
Celgene common stock. The exercise of these rights becomes economically
attractive upon the triggering of


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certain "flip-in" or "flip-over" rights which work in conjunction with the
shareholder rights plan's basic provisions. The flip-in rights will permit their
holders to purchase shares of common stock at a discounted rate, resulting in
substantial dilution of an acquiror's voting and economic interests in Celgene.
The flip-over element of the shareholder rights plan involves some mergers or
significant asset purchasers, which trigger certain rights to purchase shares of
the acquiring or surviving company at a discount. The shareholder rights plan
contains a "permitted offer" exception which allows offers determined by
Celgene's board of directors to be in its best interests and its stockholders to
take place free of the diluting effects of the shareholder rights plan's
mechanisms. Celgene's board of directors retains the rights, at all times prior
to acquisition of 15% of Celgene's voting common stock by an acquiror, to
discontinue the shareholder rights plan through the redemption of all rights, or
to amend the shareholder rights plan in any respect.


DELAWARE LAW AND SELECTED BY-LAW PROVISIONS

Celgene's board of directors has adopted certain amendments to its by-laws
intended to strengthen its board of directors' position in the event of a
hostile takeover attempt. These by-law provisions have the following effects:

o  they provide that only persons who are nominated in accordance with the
   procedures set forth in the by-laws shall be eligible for election as Celgene
   directors, except as may be otherwise provided in the by-laws;

o  they provide that only business brought before the annual meeting by
   Celgene's board of directors or by a stockholder who complies with the
   procedures set forth in the by-laws may be transacted at an annual meeting of
   stockholders;

o  they provide that only the chairman of the board, if any, the chief executive
   officer, the president, the secretary or a majority of Celgene's board of
   directors may call special meetings of Celgene stockholders;

o  they establish a procedure for Celgene's board of directors to fix the record
   date whenever stockholder action by written consent is undertaken; and

o  they require a vote of holders of two-thirds of the outstanding share of
   common stock to amend certain by-law provisions.

Furthermore, Celgene is subject to the provisions of Section 203 of the Delaware
General Corporation Law, an anti-takeover law. In general, the statute prohibits
a publicly held Delaware corporation from engaging in a "business combination"
with an "interested stockholder" for a period of three years after the date of
the transaction in which the person became an interested stockholder, unless the
business combination is approved in a prescribed manner. For purposes of Section
203, a "business combination" included a merger, asset sale or other transaction
resulting in a financial benefit to the interested stockholder, and an
"interested stockholder" is a person who, together with affiliates and
associates, owns or within three years prior, did own, 15% or more of the
corporation's voting stock.


TRANSFER AGENT AND REGISTRAR

The transfer agent and registrar for the Celgene common stock is American Stock
Transfer & Trust Company. It is located at 40 Wall St., 46th Floor, New York,
NY, 10005, and its telephone number is (718) 921-8200.


                   COMPARATIVE RIGHTS OF CELGENE STOCKHOLDERS
                             AND SIGNAL SHAREHOLDERS

After the merger, the Signal shareholders will become stockholders of Celgene
and the Signal shareholders' rights will cease to be defined and governed by the
California General Corporation Law, and instead be defined and governed by the
Delaware General Corporation Law. In addition,


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rights of the Signal shareholders will no longer be defined and governed by
Signal's amended and restated articles of incorporation and by-laws. Instead,
each shareholder will become a stockholder of Celgene whose rights as a
stockholder will be defined and governed by Celgene's certificate of
incorporation, as amended, and by-laws. While the rights and privileges of
stockholders of a Delaware corporation (such as Celgene) are, in many instances,
comparable to those of shareholders of a California corporation (such as
Signal), there are differences. The following is a summary of the material
differences between the rights of holders of Signal capital stock and the rights
of holders of Celgene common stock at the date of this proxy
statement/prospectus. These differences arise from differences between Delaware
law and California law and between the Celgene certificate of incorporation and
the Celgene by-laws on the one hand and the Signal amended and restated articles
of incorporation and the Signal by-laws on the other.


SIZE OF THE BOARD OF DIRECTORS

Under California law, changes in the number of directors of a corporation must
generally be approved by a majority of the outstanding shares, although a board
of directors may fix the exact number of directors within a range stated in the
corporation's articles of incorporation or by-laws if that stated range has been
approved by the corporation's shareholders. Delaware law permits a corporation's
board of directors alone to change the authorized number or range of directors
by amendment of the corporation's by-laws, unless otherwise prohibited by the
corporation's certificate of incorporation (in which case a change in the number
of directors may be made only upon approval by the stockholders). In any case,
no reduction in the authorized number of directors may have the effect of
removing any director before that director's term of office expires. The ability
of the board of directors to change the number of directors without stockholder
approval enables a corporation to respond quickly to a potential opportunity to
attract the services of a qualified director or to eliminate a vacancy for which
a suitable candidate is not available.

The Signal by-laws provide for a board of directors within a range of five to
nine. The exact number of directors is currently set at seven. Directors are
elected at each annual meeting of the Signal shareholders. The stated range may
be changed only by amending the Signal by-laws, which requires the approval of
the Signal shareholders. The Celgene board currently consists of nine members.
Directors are elected at each annual meeting of Celgene stockholders. The number
of directors of the Celgene board may be changed by resolution by the Celgene
board of directors.


ELIMINATION OF CUMULATIVE VOTING

California law provides for cumulative voting in the election of directors,
unless, in the case of a listed corporation, its articles of incorporation or
by-laws provide otherwise. Because Signal is not a listed corporation, Signal
shareholders are entitled to cumulative voting in the election of directors.

Under Delaware law, cumulative voting is not mandatory, and a corporation's
certificate of incorporation must provide for cumulative voting rights if
stockholders are to be entitled to such rights. The Celgene certificate of
incorporation does not provide for cumulative voting.


REMOVAL OF DIRECTORS

Under California law, any director or the entire board of directors may be
removed, with or without cause, with the approval of a majority of the
outstanding shares entitled to vote. However, no individual director may be
removed (unless the entire board is removed) if the number of votes cast against
removal would be sufficient to elect the director under cumulative voting,
whether or not the corporation's articles of incorporation or by-laws provide
for cumulative voting. A corporation's board of directors may not remove a
director unless the director has been declared of unsound mind by an order of
court or convicted of a felony.

Stockholders of a Delaware corporation holding a majority of the outstanding
shares entitled to vote for directors may remove a director with or without
cause, except in cases involving classified boards or where cumulative voting is
permitted. The Celgene by-laws provide for removal with or without cause.


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FILLING NEW SEATS OR VACANCIES ON THE BOARD OF DIRECTORS

Unless otherwise provided in a corporation's articles of incorporation or
by-laws, under California law, any vacancy on a board of directors other than
one created by removal of a director may be filled by the remainder of the
corporation's board of directors. A vacancy created by removal of a director may
be filled by the board of directors only if the board is so authorized by the
corporation's articles of incorporation or by a by-law approved by the
corporation's shareholders.

Under Delaware law, vacancies and newly created directorships may be filled by a
majority of the directors then in office (even though less than a quorum),
unless (i) otherwise provided in the corporation's certificate of incorporation
or by-laws, or (ii) the certificate of incorporation directs that a particular
class is to elect the director, in which case any other directors elected by
that class, or a sole remaining director, must fill the vacancy.

The Signal by-laws provide that vacancies in the Signal board of directors may
be filled by a majority of the remaining directors, even if less than a quorum,
or by a sole remaining director; however, a vacancy created by the removal of a
director by the shareholders may be filled only by a vote of the shareholders.

The Celgene by-laws provides that new seats on the Celgene board of directors or
vacancies occurring for any cause may be filled by an affirmative vote of the
majority of stockholders generally entitled to vote in the election of
directors, or by the affirmative vote of a majority of the directors then in
office, even though less than a quorum. Newly created directorships resulting
from any increase in the authorized number of directors are filled only by the
affirmative vote of the directors then in office, even though less than a quorum
of the board.

INDEMNIFICATION AND LIMITATION OF LIABILITY

California and Delaware have similar laws governing indemnification by a
corporation of its officers, directors, employees and other agents. The laws of
both states also permit, with exceptions, a corporation to adopt charter
provisions eliminating the liability of its directors to the corporation or its
stockholders for monetary damages for breach of the directors' fiduciary duty of
care. There are nonetheless certain differences between the laws of the two
states respecting indemnification and limitation of liability, which are
summarized below.

The Signal articles of incorporation eliminate the liability of directors to the
corporation to the fullest extent permissible under California law. California
law does not permit the elimination of monetary liability based on:

   o intentional misconduct or knowing and culpable violation of law;

   o acts or omissions that a director believes to be contrary to the best
     interests of the corporation or its shareholders or that involve the
     absence of good faith on the part of the director;

   o receipt of an improper personal benefit;

   o acts or omissions that show reckless disregard for the director's duty to
     the corporation or its shareholders, where the director in the ordinary
     course of performing a director's duties should be aware of a risk of
     serious injury to the corporation or its shareholders;

   o acts or omissions that constitute an unexcused pattern of inattention that
     amounts to an abdication of the director's duty to the corporation and its
     shareholders;

   o transactions between the corporation and a director who has a material
     financial interest in the transaction; and

   o liability for improper distributions, loans or guarantees.

The Celgene certificate of incorporation eliminates the liability of directors
to Celgene or its stockholders for monetary damages for breach of fiduciary duty
as a director to the fullest extent permissible under Delaware law. Under
Delaware law, such provision may not eliminate or limit director monetary
liability for:


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   o breaches of the director's duty of loyalty to the corporation or its
     stockholders;

   o acts or omissions not in good faith or involving intentional misconduct or
     knowing violations of law;

   o the payment of unlawful dividends or unlawful stock repurchases or
     redemptions; or

   o transactions in which the director received an improper personal benefit.
     The limitation of liability provisions also may not limit a director's
     liability for violation of, or otherwise relieve Celgene or its directors
     from the necessity of complying with, federal or state securities laws, or
     affect the availability of nonmonetary remedies such as injunctive relief
     or rescission.

California law permits a California corporation to provide rights to
indemnification beyond those provided by law to the extent the additional
indemnification is authorized in the corporation's articles of incorporation.
Thus, California corporations may, by agreements or by-law provisions, make
mandatory the permissive indemnification provided by California law. The Signal
articles of incorporation permit indemnification beyond that expressly mandated
by California law, subject only to the limits on excess indemnification under
California law.

The Signal by-laws also contain indemnification provisions consistent with those
set forth in its charter. Both Delaware and California law state that the
indemnification provided by statute is not exclusive of any other rights under
any by-law, agreement, vote of shareholders, or of disinterested directors, or
otherwise.


INTERESTED DIRECTOR TRANSACTIONS

Under both California and Delaware law, contracts or transactions in which one
or more of a corporation's directors have an interest are not void or voidable
because of that interest if certain conditions are met. The conditions are
generally similar under California and Delaware law. Under California and
Delaware law, (a) either the shareholders or the board of directors must approve
the contract or transaction after full disclosure of the material facts, and, in
the case of board approval, the contract or transaction must also be "just and
reasonable" (in California) or "fair" (in Delaware) to the corporation, or (b)
the contract or transaction must have been "just and reasonable" or "fair" (as
applicable) as to the corporation at the time it was approved. In the latter
case, California law explicitly places the burden of proof on the interested
director. Under California law, if shareholder approval is sought, the
interested director is not entitled to vote his shares on any action regarding
the contract or transaction. If board approval is sought, the contract or
transaction must be approved by a majority vote of a quorum of the directors,
without counting the vote of any interested directors (except that interested
directors may be counted for purposes of establishing a quorum). Under Delaware
law, if stockholder approval is sought generally, the contract or transaction
must be approved in good faith by a majority of disinterested stockholders. If
board approval is sought, the contract or transaction must be approved by a
majority of the disinterested directors (even though less than a majority of a
quorum). Therefore, transactions that the Signal board of directors might not be
able to approve because of the number of interested directors could be approved
by a majority of the disinterested directors of Celgene, although less than a
majority of a quorum.


LOANS TO OFFICERS AND EMPLOYEES

Under California law, a corporation cannot make any loan or guaranty to or for
the benefit of a director or officer of the corporation or its parent unless the
loan or guaranty, or a plan providing for the loan or guaranty, is approved by
shareholders owning a majority of the outstanding shares of the corporation.
However, under California law, any corporation with 100 or more shareholders of
record may seek shareholder approval of a by-law provision authorizing the board
of directors alone to approve loans or guarantees to or on behalf of officers
(whether or not the officers are directors) if the board determines that any
loan or guaranty may reasonably be expected to benefit the corporation. The
Signal by-laws currently authorize the Signal board of directors to approve such
loans or guarantees.


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Under Delaware law, a corporation may make loans to, guaranty the obligations
of, or otherwise assist its officers or other employees and those of its
subsidiaries (including directors who are also officers or employees) when such
action, in the judgement of the directors, may reasonably be expected to benefit
the corporation.


STOCKHOLDER DERIVATIVE SUITS

California law provides that a shareholder bringing a derivative action on
behalf of a corporation need not have been a shareholder at the time of the
transaction in question, provided that certain tests are met. Under Delaware
law, a stockholder may bring a derivative action on behalf of the corporation
only if the stockholder was a stockholder of the corporation at the time of the
transaction in question or his or her stock thereafter devolved upon him or her
by operation of law. California law also provides that the corporation or the
defendant in a derivative suit may make a motion to the court for an order
requiring the plaintiff shareholder to furnish a security bond. Delaware does
not have a similar bond requirement.


ELIMINATION OF ACTIONS BY WRITTEN CONSENT OF STOCKHOLDERS

Under both California and Delaware law, shareholders may act by written consent
in lieu of a shareholder meeting. Both California and Delaware law permit a
corporation in its charter to eliminate actions by written consent. Neither
Signal nor Celgene has eliminated actions by written consent.


POWER TO CALL SPECIAL MEETINGS OF STOCKHOLDERS

Under California law and the Signal by-laws, a special meeting of shareholders
may be called by the board of directors, the chairman of the board, the
president, two or more members of the board, or by one or more holders of shares
entitled to cast not less than 10% of the votes at such meeting.

Under Delaware law, special meetings of stockholders may be called by a
corporation's board of directors or by the other person or persons authorized by
the corporation's certificate of incorporation or by-laws. Celgene's by-laws
provide that special meetings of stockholders may be called by the chairman of
the board, the chief executive officer, the president, the secretary or a
majority of directors.


STOCKHOLDER APPROVAL OF CERTAIN BUSINESS COMBINATIONS

In recent years, a number of states have adopted special laws designed to make
certain kinds of "unfriendly" corporate takeovers, or other transactions
involving a corporation and one or more of its significant shareholders, more
difficult. Under Section 203 of the Delaware law, certain "business
combinations" with "interested stockholders" of Delaware corporations are
subject to a three-year moratorium unless specified conditions are met. Under
Section 203 of the Delaware law, certain business combinations with a majority
shareholder require the delivery of a fairness opinion; however, there is no
equivalent provision in California law to Section 203, which addresses business
combinations with a significant but not majority holder.

Section 203 prohibits a Delaware corporation from engaging in a "business
combination" with an "interested stockholder" for three years following the date
that the person becomes an interested stockholder. With certain exceptions, an
interested stockholder is a person or group who or which owns 15% or more of the
corporation's outstanding voting stock (including any rights to acquire stock
under an option, warrant, agreement, arrangement or understanding, or upon the
exercise of conversion or exchange rights, and stock with respect to which the
person has voting rights only), or is an affiliate or associate of the
corporation and was the owner of 15% or more of the voting stock at any time
within the previous three years.

For purposes of Section 203, the term "business combination" is defined broadly
to include mergers with or caused by the interested stockholder; sales or other
dispositions to the interested stockholder (except proportionately with the
corporation's other stockholders) of assets of the corporation or a


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subsidiary equal to 10% or more of the total market value of the corporation's
consolidated assets or its outstanding stock; the issuance or transfer by the
corporation or a subsidiary of stock of the corporation or the subsidiary to the
interested stockholder (except for transfers in a conversion or exchange or a
pro rata distribution or certain other transactions, none of which increase the
interested stockholder's proportionate ownership of any class or series of the
corporation's or such subsidiary's stock); or receipt by the interested
stockholder of the benefit (except proportionately as a stockholder), directly
or indirectly, of any loans, advances, guarantees, pledges, or other financial
benefits provided by or through the corporation or a subsidiary.

The three-year moratorium imposed on business combinations by Section 203 does
not apply if (a) before the stockholder becomes an interested stockholder, the
board of directors approves either the business combination or the transaction
which resulted in the person becoming an interested stockholder; (b) the
interested stockholder owns 85% of the corporation's voting stock upon
completion of the transaction which made him or her an interested stockholder
(excluding from the 85% calculation shares owned by directors who are also
officers of the target corporation and shares held by employee stock plans which
do not permit employees to decide confidentially whether to accept a tender or
exchange offer); or (c) after the person becomes an interested stockholder, the
board approves the business combination, and it is also approved at a
stockholder meeting by 66 2/3% of the voting stock not owned by the interested
stockholder.

Section 203 only applies to Delaware corporations which, like Celgene, (a) have
a class of voting stock that is listed on a national securities exchange, are
quoted on an interdealer quotation system such as the Nasdaq National Market or
(b) are held of record by more than 2,000 shareholders. However, a Delaware
corporation may elect not to be governed by Section 203 by a provision in its
original certificate of incorporation or an amendment or in its by-laws, which
amendment must be approved by majority shareholder vote and may not be further
amended by the board of directors. Celgene has not elected not to be governed by
Section 203; therefore, Section 203 will apply to Celgene.

Section 203 has been challenged in lawsuits arising out of ongoing takeover
disputes, and it is not yet clear whether and to what extent its
constitutionality will be upheld by the courts. Although the United States
District Court for the District of Delaware has consistently upheld the
constitutionality of Section 203, the Delaware Supreme Court has not yet
considered the issue. Section 203 has the effect of limiting the ability of a
potential acquiror to make a two-tiered bid for Celgene in which all
stockholders would not be treated equally. Signal shareholders should note that
the application of Section 203 to Celgene will confer upon the Celgene board the
power to reject a proposed business combination, even though a potential
acquiror could be offering a substantial premium for Celgene's shares over the
then current market price (assuming the stock is then publicly traded). Section
203 may also discourage certain potential acquirors unwilling to comply with its
provisions.


MERGERS

Both California and Delaware law generally require that a majority of the
holders of the stock of each of the acquiring and target corporations approve
statutory mergers. Delaware law does not require a stockholder vote of the
surviving corporation in a merger (unless the corporation provides otherwise in
its certificate of incorporation) if:

     o the merger agreement does not amend the existing certificate of
       incorporation,

     o each share of the surviving corporation outstanding before the merger is
       an identical outstanding share after the merger, and

     o the number of shares to be issued by the surviving corporation in the
       merger does not exceed 20% of the shares outstanding immediately before
       the merger. California law contains a similar exception to its voting
       requirements for reorganizations where shareholders or the corporation
       itself, or both, immediately before the reorganization own immediately
       after the reorganization equity securities constituting more than
       five-sixths of the voting power of the surviving or acquiring corporation
       or its parent entity.


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Both California and Delaware law also require that a sale of all or
substantially all of the assets of a corporation be approved by a majority of
the voting shares of the corporation transferring such assets.

With exceptions, California law also requires that mergers, reorganizations,
certain sales of assets and similar transactions be approved by a majority vote
of each class of shares outstanding. The Signal Amended and Restated Articles of
Incorporation and California law require the approval of the holders of at least
a majority of the Signal common stock and at least a majority of the Signal
preferred stock.

By contrast, Delaware law generally does not require class voting, except in
certain transactions involving an amendment to the certificate of incorporation
which adversely affects a specific class of shares. The Celgene certificate of
incorporation does not require class voting.


DISSENTERS' RIGHTS

Under both California and Delaware law, a stockholder of a corporation
participating in major corporate transactions may, under varying circumstances,
be entitled to dissenters' rights under which the shareholder may receive cash
in the amount of the fair market value of his, her or its shares in lieu of the
consideration paid in the transaction.

The limitations on the availability of dissenters' rights under California law
are different from those under Delaware law. Shareholders of a California
corporation whose shares are not listed on a national securities exchange or on
a list of over-the-counter margin stocks issued by the Board of Governors of the
Federal Reserve System generally have dissenters' rights in certain instances.
As a result, dissenters' rights are available to the Signal shareholders with
respect to the merger. See "Dissenters' Rights" below and the California General
Corporation Law, Sections 1300 through 1312, a copy of which is attached to this
proxy statement/prospectus as Appendix B.

Under Delaware law, dissenters' rights are not available (a) with respect to the
sale, lease or exchange of all or substantially all of the assets of a
corporation, (b) with respect to a merger or consolidation by a corporation
whose shares are either listed on a national securities exchange or are held of
record by more than 2,000 holders if the stockholders receive only shares of the
surviving corporation or shares of any other corporation which are either listed
on a national securities exchange or held of record by more than 2,000 holders,
plus cash in lieu of fractional shares, or (c) to stockholders of a corporation
surviving a merger if, among other conditions, no vote of the stockholders of
the surviving corporation is required to approve the merger.

THIS SUMMARY OF THE MATERIAL DIFFERENCES IN THE CORPORATION LAWS OF CALIFORNIA
AND DELAWARE, THE SIGNAL ARTICLES AND THE CELGENE CERTIFICATE AND THE SIGNAL
BY-LAWS AND THE CELGENE BY-LAWS DOES NOT PURPORT TO BE A COMPLETE LISTING OF
DIFFERENCES IN THE RIGHTS AND REMEDIES OF HOLDERS OF SHARES OF CALIFORNIA, AS
OPPOSED TO DELAWARE, CORPORATIONS AND SHAREHOLDERS OF SIGNAL AND STOCKHOLDERS OF
CELGENE IN PARTICULAR. THE DIFFERENCES CAN BE DETERMINED IN FULL BY REFERENCE TO
CALIFORNIA LAW, TO DELAWARE LAW AND THE SIGNAL ARTICLES AND THE CELGENE
CERTIFICATE AND THE SIGNAL BY-LAWS AND THE CELGENE BY-LAWS. IN ADDITION, THE
LAWS OF CALIFORNIA AND DELAWARE PROVIDE THAT SOME OF THE STATUTORY PROVISIONS AS
THEY AFFECT VARIOUS RIGHTS OF HOLDERS OF SHARES MAY BE MODIFIED BY PROVISIONS IN
THE ARTICLES OF INCORPORATION OR BY-LAWS OF THE CORPORATION.



                                  OTHER MATTERS

As of the date of this proxy statement/prospectus, the Signal board knows of no
matters that will be presented for consideration at the Signal meeting, other
than as described in this proxy statement/prospectus. If any other matters
properly come before the Signal meeting and are voted


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upon, the enclosed proxies will be deemed to confer discretionary authority on
the individuals named as proxies therein to vote the shares represented by such
proxies as to any such matters. The individuals named as proxies intend to vote
or not to vote in accordance with the recommendation of the management of
Signal.



                                  LEGAL MATTERS

The validity of the Celgene common stock issuable under the merger and certain
legal matters relating to the merger and the transactions contemplated thereby
have been passed upon for Celgene by Proskauer Rose LLP, New York, New York.
Cooley Godward, LLP, San Diego, California, is acting as counsel to Signal in
connection with the merger and the transactions contemplated thereby.


                                     EXPERTS

The consolidated financial statements and schedule of Celgene Corporation and
subsidiary as of December 31, 1999 and 1998, and for each of the years in the
three-year period ended December 31, 1999, have been incorporated by reference
herein and in the registration statement, in reliance upon the report of KPMG
LLP, independent certified public accountants, and upon the authority of said
firm as experts in accounting and auditing.

Ernst & Young LLP, independent  auditors,  have audited Signal  Pharmaceuticals,
Inc.'s  financial  statements at December 31, 1999 and 1998, and for each of the
three years in the period ended December 31, 1999, as set forth in their report.
Signal's    financial    statements   have   been   included   in   this   proxy
statement/prospectus and elsewhere in this registration statement in reliance on
Ernst & Young LLP's  report,  given on their  authority as experts in accounting
and auditing.

The statements in this prospectus under the caption "Risk Factors--The combined
company may not be able to protect its intellectual property" have been reviewed
and approved by Mathews, Collins, Shepherd & Gould, P.A. and are included herein
in reliance upon such review and approval.

The statements in this prospectus that relate to thalidomide U.S. patent rights
licensed from The Rockefeller University and EntreMed/Children's Medical Center
Corp. under the caption "Risk Factors--The combined company may not be able to
protect its intellectual property" have been reviewed and approved by Pennie &
Edmonds LLP as special patent counsel to Celgene Corporation for these matters,
and are included herein in reliance upon their review and approval as experts in
U.S. patent law.

The statements in this prospectus under the caption "Risks Relating to Investing
in the Pharmaceutical Industry--The pharmaceutical and agrochemical industries
are subject to extensive government regulation and there is no assurance of
regulatory approval" have been reviewed and approved by Kleinfeld, Kaplan &
Becker, as experts in such matters, and are included herein in reliance upon
such review and approval as experts in U.S. patent law.


                       WHERE YOU CAN FIND MORE INFORMATION

Celgene files reports with the SEC on a regular basis that contain financial
information about it and its results of operations. You may read or copy any
document that Celgene files with the SEC at the SEC's Public Reference Room at
450 Fifth Street, N.W., Washington, D.C. 20549 and 7 World Trade Center, Suite
1300, New York, New York 10048. You may obtain information about the Public
Reference Room by calling the SEC for more information at 1-800-SEC-0330.
Celgene's SEC filings are also available at the SEC's web site at
http://www.sec.gov.

The SEC allows Celgene to "incorporate by reference" the information it files
with them, which means that Celgene can disclose important information to you by
referring you to those documents. The information incorporated by reference is
considered to be part of this prospectus, and


                                       94
<PAGE>

information that Celgene files later with the SEC will automatically update and
supersede this information. Celgene is incorporating by reference the documents
listed below and any future filings that Celgene will make with the SEC under
Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934:

o Annual Report on Form 10-K for the fiscal year ended December 31, 1999,

o Quarterly Report on Form 10-Q for the fiscal quarter ended March 31, 2000;

o Current Report on Form 8-K filed January 27, 2000;

o Current Report on Form 8-K filed February 10, 2000;

o Current Report on Form 8-K filed February 10, 2000;

o Current Report on Form 8-K filed February 22, 2000; and

o Proxy Statement for 2000 Annual Meeting filed May 5, 2000.

You may request a copy of these filings, at no cost, by writing or telephoning
Celgene's Secretary at the following address:

   Celgene Corporation
   7 Powder Horn Drive
   Warren, NJ 07059
   (732) 271-1001

This prospectus is part of a registration statement on Form S-4 Celgene filed
with the Securities and Exchange Commission. You should rely only on the
information or representations provided in this prospectus. Celgene has
authorized no one to provide you with different information. Celgene is not
making an offer of these securities in any state where the offer is not
permitted. You should not assume that the information in this prospectus is
accurate as of any date other than the date on the front of the document.


                           FORWARD-LOOKING STATEMENTS

Each of Signal and Celgene has made forward-looking statements in this proxy
statement/ prospectus, and in documents that are incorporated by reference in
this proxy statement/prospectus, that are subject to risks and uncertainties.
All statements included or incorporated by reference in this proxy
statement/prospectus or made by management of Celgene or Signal other than
statements of historical fact regarding Celgene, Signal or the combined company
are forward-looking statements. Examples of forward-looking statements include
statements regarding Celgene's, Signal's or the combined company's future
financial results, operating results, product successes, business strategies,
projected costs, future products, competitive positions and plans and objectives
of management for future operations. In some cases, you can identify
forward-looking statements by terminology, such as "may," "will," "should,"
"would," "expects," "plans," "anticipates," "believes," "estimates," "predicts,"
"potential," or "continue" or the negative of these terms or other comparable
terminology. Any expectations based on these forward-looking statements are
subject to risks and uncertainties and other important factors, including those
discussed in the "Risk Factors" section of this proxy statement/prospectus.
These and many other factors could affect the future financial and operating
results of Celgene, Signal or the combined company. These factors could cause
actual results to differ materially from expectations based on forward-looking
statements made in this document or elsewhere by or on behalf of Celgene, Signal
or the combined company.


                                       95
<PAGE>
*********


                                   APPENDIX A


                          AGREEMENT AND PLAN OF MERGER


                                  BY AND AMONG



                              CELGENE CORPORATION,



                           CELGENE ACQUISITION CORP.



                                       AND



                          SIGNAL PHARMACEUTICALS, INC.



                              DATED JUNE 29, 2000
<PAGE>

                                TABLE OF CONTENTS



<TABLE>
<CAPTION>
                                                                                   PAGE
                                                                                  -----
<S>             <C>                                                               <C>
ARTICLE I

 THE MERGER                                                                         1
 Section 1.1    The Merger                                                          1
 Section 1.2.   Effective Time of the Merger                                        1
 Section 1.3.   Closing                                                             2
 Section 1.4.   Plan of Reorganization                                              2

ARTICLE II

 THE SURVIVING CORPORATION                                                          2
 Section 2.1    Articles of Incorporation                                           2
 Section 2.2    Bylaws                                                              2
 Section 2.3    Directors and Officers of Surviving Corporation                     2

ARTICLE III

 CONVERSION OF SHARES                                                               2
 Section 3.1    Exchange Ratio                                                      2
 Section 3.2    Exchange of Company Common Stock; Procedures                        3
 Section 3.3    Dividends; Transfer Taxes; Escheat                                  3
 Section 3.4    No Fractional Securities                                            4
 Section 3.5    Closing of Company Transfer Books                                   4
 Section 3.6    Further Assurances                                                  4

ARTICLE IV

 REPRESENTATIONS AND WARRANTIES OF THE COMPANY                                      5
 Section 4.1    Organization                                                        5
 Section 4.2    Capitalization                                                      5
 Section 4.3    Authority Relative to this Agreement                                6
 Section 4.4    Consents and Approvals; No Violations                               6
 Section 4.5    Financial Statements                                                6
 Section 4.6    Absence of Certain Changes or Events; Material Contracts            7
 Section 4.7    Litigation                                                          7
 Section 4.8    Absence of Undisclosed Liabilities                                  7
 Section 4.9    No Default                                                          7
 Section 4.10   Taxes                                                               7
 Section 4.11   Title to Properties; Encumbrances                                   8
 Section 4.12   Intellectual Property                                               9
 Section 4.13   Compliance with Applicable Law                                      9
 Section 4.14   Material Contracts                                                  9
 Section 4.15   FDA Matters                                                        10
 Section 4.16   Information in Disclosure Documents and Registration Statements    10
 Section 4.17   Employee Benefit Plans; ERISA                                      11
 Section 4.18   Environmental Laws and Regulations                                 12
 Section 4.19   Vote Required                                                      13
 Section 4.20   Opinion of Financial Advisor                                       13
 Section 4.21   Accounting Matters                                                 13
 Section 4.22   Labor Matters                                                      13
 Section 4.23   Affiliate Transactions                                             13
</TABLE>

                                        i
<PAGE>


<TABLE>
<CAPTION>
                                                                                     PAGE
                                                                                    -----
<S>              <C>                                                                <C>
 Section 4.24    Brokers                                                             13
 Section 4.25    Tax Matters                                                         13
ARTICLE V

 REPRESENTATIONS AND WARRANTIES OF PARENT AND MERGER SUB                             14
 Section 5.1     Organization                                                        14
 Section 5.2     Capitalization                                                      14
 Section 5.3     Authority Relative to this Agreement                                14
 Section 5.4     Consents and Approvals; No Violations                               15
 Section 5.5     Reports and Financial Statements                                    15
 Section 5.6     Absence of Certain Changes or Events                                15
 Section 5.7     Information in Disclosure Documents and Registration Statement      15
 Section 5.8     Compliance with Applicable Law                                      16
 Section 5.9     Litigation                                                          16
 Section 5.10    Opinion of Financial Advisor                                        16
 Section 5.11    Accounting Matters                                                  16
 Section 5.12    Tax Matters                                                         16
 Section 5.13    Brokers                                                             16
ARTICLE VI

 CONDUCT OF COMPANY BUSINESS PENDING THE MERGER                                      16

ARTICLE VII

 ADDITIONAL AGREEMENTS                                                               18
 Section 7.1     Access and Information                                              18
 Section 7.2     No Solicitation                                                     18
 Section 7.3     Registration Statement                                              18
 Section 7.4     Tax Matters                                                         19
 Section 7.5     Proxy Statements; Stockholder Approval                              19
 Section 7.6     Compliance with the Securities Act                                  19
 Section 7.7     Reasonable Best Efforts                                             20
 Section 7.8     Voting and Proxy Agreement; Option Agreement                        20
 Section 7.9     Company Stock Options                                               20
 Section 7.10    Public Announcements                                                21
 Section 7.11    Expenses                                                            21
 Section 7.12    Listing Application                                                 21
 Section 7.13    Supplemental Disclosure                                             21
 Section 7.14    Letters of Accountants                                              21
 Section 7.15    Indemnification                                                     22
 Section 7.16.   Other Agreements                                                    22
ARTICLE VIII

 CONDITIONS  TO  CONSUMMATION  OF THE MERGER 22 Section 8.1  Conditions  to Each
 Party's   Obligation  to  Effect  the  Merger  22  Section  8.2  Conditions  to
 Obligations of Parent and Sub to Effect the Merger 23 Section 8.3 Conditions to
 Obligation of the Company to Effect the Merger 24

</TABLE>

                                       ii
<PAGE>


<TABLE>
<CAPTION>
                                                                                    PAGE
                                                                                   -----
<S>                     <C>                                                        <C>
ARTICLE IX

 TERMINATION                                                                        25
 Section 9.1            Termination                                                 25
 Section 9.2            Effect of Termination                                       25
ARTICLE X

 GENERAL PROVISIONS                                                                 26
 Section 10.1           Amendment and Modification                                  26
 Section 10.2           Waiver                                                      26
 Section 10.3           Survivability; Investigations                               26
 Section 10.4           Notices                                                     26
 Section 10.5           Descriptive Headings; Interpretation                        27
 Section 10.6           Entire Agreement; Assignment                                27
 Section 10.7           Governing Law                                               27
 Section 10.8           Severability                                                27
 Section 10.9           Counterparts                                                27

EXHIBITS
 Exhibit A-1            Form of Voting and Proxy Agreement
 Exhibit A-2            Form of Options Agreement
 Exhibit B              Form of Tax Representation Letters
 Exhibit C              Form of Affiliate Agreement
 Exhibit D              Opinion of Cooley Godward LLP
 Exhibit E              Form of Tax Opinion of Proskauer Rose LLP
 Exhibit F              Form of Opinion of Proskauer Rose LLP
 Exhibit G              Form of Tax Opinion of Cooley Godward LLP
SCHEDULES

 REPRESENTATIONS AND WARRANTIES OF THE COMPANY
 Schedule 4.1           Organization
 Schedule 4.2(b)(i)     Capitalization
 Schedule 4.2(b)(ii)    Capitalization
 Schedule 4.2(b)(iii)   Capitalization
 Schedule 4.2(c)        Capitalization
 Schedule 4.3           Authority Relative to Agreement
 Schedule 4.4           Consents and Approvals; No Violations
 Schedule 4.5           Financial Statements
 Schedule 4.6           Absence of Certain Changes or Events; Material Contracts
 Schedule 4.7           Litigation
 Schedule 4.8           Absence of Undisclosed Liabilities
 Schedule 4.9           No Default
 Schedule 4.10          Taxes
 Schedule 4.11          Title to Properties; Encumbrances
 Schedule 4.12(a)(i)    Intellectual Property
 Schedule 4.12(a)(ii)   Intellectual Property
 Schedule 4.12(b)       Intellectual Property
 Schedule 4.12(c)       Intellectual Property
 Schedule 4.12(d)       Intellectual Property
 Schedule 4.13          Compliance with Applicable Law
</TABLE>

                                       iii
<PAGE>


<TABLE>
<CAPTION>
                                                                                          PAGE
                                                                                         -----
<S>                     <C>                                                              <C>
 Schedule 4.14          Material Contracts
 Schedule 4.15          FDA Matters
 Schedule 4.16          Information in Disclosure Documents and RegistrationStatements
 Schedule 4.17          Employee Benefit Plans; ERISA
 Schedule 4.18          Environmental Laws and Regulations
 Schedule 4.19          Vote Required
 Schedule 4.21          Accounting Matters
 Schedule 4.22          GCL Chapter 13
 Schedule 4.23          Labor Matters
 Schedule 4.24          Affiliate Transactions
 Schedule 4.25          Brokers
 Schedule 4.26          Tax Matters
SCHEDULES

 REPRESENTATIONS  AND  WARRANTIES  OF PARENT AND MERGER SUB  Schedule  5.2(c)(i)
 Capitalization   Schedule  5.2(c)(ii)   Capitalization   Schedule   5.2(c)(iii)
 Capitalization  Schedule 5.4 Consents and Approvals; No Violations Schedule 5.5
 Absence of Certain Changes or Events
 Schedule 5.6           Information in Disclosure Documents and Registration
 Schedule 5.7           Compliance with Applicable Law
 Schedule 5.8           Litigation
 Schedule 5.10          Accounting Matters
 Schedule 5.11          Tax Matters
 Schedule 5.12          Brokers

</TABLE>

                                       iv
<PAGE>

                          AGREEMENT AND PLAN OF MERGER

     AGREEMENT AND PLAN OF MERGER dated June 29, 2000, by and among Celgene
Corporation, a Delaware corporation ("Parent"), Celgene Acquisition Corp., a
California corporation and wholly-owned subsidiary of Parent ("Sub"), and Signal
Pharmaceuticals, Inc., a California corporation (the "Company").

     The Boards of Directors of Parent, Sub and the Company deem it advisable
and in the best interests of their respective stockholders that Parent acquire
the Company pursuant to the terms and conditions of this Agreement, and, in
furtherance of such acquisition, such Boards of Directors have unanimously
approved the merger of Sub with and into the Company in accordance with the
terms of this Agreement and the California General Corporation Law (the "GCL").


     Concurrently with the execution and delivery of this Agreement and as a
condition and inducement to Parent's willingness to enter into this Agreement,
(i) the holders of the shares of the Common Stock of the Company (the "Company
Common Stock"), the Series A Preferred Stock of the Company, the Series B
Preferred Stock of the Company, the Series C Preferred Stock of the Company, the
Series D Preferred Stock of the Company, the Series E Preferred Stock of the
Company, the Series F Preferred Stock of the Company, and the Series F-1
Preferred Stock of the Company, (collectively, the "Company Preferred Stock"),
with sufficient voting power to approve the Merger (as defined in Section 1.1
hereof) and the conversion of the Company Preferred Stock to Company Common
Stock, are entering into an agreement with Parent in the form attached hereto as
Exhibit A-1 (the "Voting and Proxy Agreement") granting Parent the right to vote
such shares of the Company Common Stock and Company Preferred Stock in
accordance with the terms set forth in the Voting and Proxy Agreement; and (ii)
the Company is entering into an agreement with the Parent in the form attached
hereto as Exhibit A-2 (the "Option Agreement") granting Parent an option to
purchase 2,000,000 shares of Company Common Stock and stock appreciation rights
with respect to 3,000,000 shares of Company Common Stock in accordance with the
terms set forth in the Option Agreement.

     For federal income tax purposes, it is intended that the Merger (as defined
in Section 1.1) shall qualify as a reorganization within the meaning of Section
368(a) of the Internal Revenue Code of 1986, as amended (the "Code").

     For accounting purposes, it is intended that the Merger shall be accounted
for as a pooling of interests.

     In consideration of the foregoing and the respective representations,
warranties, covenants and agreements set forth herein, the parties hereto agree
as follows:



                                    ARTICLE I



                                   THE MERGER

     Section 1.1. The Merger. In accordance with the provisions of this
Agreement and the GCL, at the Effective Time (as defined in Section 1.2), Sub
shall be merged with and into the Company (the "Merger"), the separate existence
of Sub shall thereupon cease, and the Company shall be the surviving corporation
in the Merger (sometimes hereinafter called the "Surviving Corporation") and
shall continue its corporate existence under the laws of the State of
California. The Merger shall have the effects set forth in Chapter 13 of the
GCL.

     Section 1.2. Effective Time of the Merger. The Merger shall become
effective at the time of filing of, or at such later time specified in, a
properly executed Agreement of Merger, in the form required by and executed in
accordance with the GCL, filed with the Secretary of State of the State of
California in accordance with the provisions of the GCL. Such filing shall be
made as soon as practicable (and in any event within two business days) after
the Closing (as defined in Section 1.3). When used in this Agreement, the term
"Effective Time" shall mean the date and time at which the Merger shall become
effective.


                                       A-1
<PAGE>

     Section 1.3. Closing. The closing of the transactions contemplated by this
Agreement (the "Closing") shall take place at the offices of Proskauer Rose LLP,
1585 Broadway, New York, New York, at 10:00 a.m., as soon as practicable (and in
any event within two business days) after the day on which all of the conditions
set forth in Article VIII are satisfied or waived or on such other date and at
such other time and place as Parent and the Company shall agree (such date, the
"Closing Date").

     Section 1.4. Plan of Reorganization. The parties to this Agreement hereby
adopt this Agreement as a "plan of reorganization" within the meaning of
Sections 1.368-2(g) and 1.368-2(a) of the United States Treasury Regulations.


                                   ARTICLE II


                            THE SURVIVING CORPORATION

     Section 2.1. Articles of Incorporation. The Articles of Incorporation of
the Company shall be the Articles of Incorporation of the Surviving Corporation
and shall be amended and restated in accordance with applicable law in such form
as Parent, in its sole discretion, shall determine.

     Section 2.2. Bylaws. The Bylaws of Sub as in effect at the Effective Time
shall be the Bylaws of the Surviving Corporation until amended in accordance
with applicable law.

     Section 2.3 Directors and Officers of Surviving Corporation.

     (a) The directors of Sub at the Effective Time shall be the initial
directors of the Surviving Corporation and shall hold office from the Effective
Time until their respective successors are duly elected or appointed and
qualified in the manner provided in the Articles of Incorporation or Bylaws of
the Surviving Corporation or as otherwise provided by law.

     (b) The officers of the Company at the Effective Time shall be the initial
officers of the Surviving Corporation and shall hold office from the Effective
Time until their respective successors are duly elected or appointed and
qualified in the manner provided in the Articles of Incorporation or Bylaws of
the Surviving Corporation, or as otherwise provided by law.


                                   ARTICLE III


                              CONVERSION OF SHARES

     Section 3.1. Exchange Ratio. At the Effective Time, by virtue of the Merger
and without any action on the part of the holder thereof:

     (a) Each share of Company Common Stock issued and outstanding immediately
prior to the Effective Time (other than shares to be canceled in accordance with
Section 3.1(b) and other than shares of Company Common Stock as to which
appraisal rights shall have been duly demanded under the GCL ("Dissenting
Shares")) shall be converted into the right to receive 0.1257 (the "Exchange
Ratio") of a share of the common stock, $.01 par value per share, of Parent
("Parent Common Stock"), payable upon the surrender of the certificate formerly
representing such share of Company Common Stock.

     (b) All shares of Company Common Stock and shares of Company Preferred
Stock that are held by the Company as treasury shares shall be canceled and
retired and cease to exist, and no securities of Parent or other consideration
shall be delivered in exchange therefor.

     (c) Each share of Common Stock of Sub ("Sub Common Stock") issued and
outstanding immediately prior to the Effective Time shall be converted into and
become one fully paid and nonassessable share of Common Stock of the Surviving
Corporation.

     (d) Each outstanding option to purchase Company Common Stock (each, a
"Company Stock Option"), and each warrant to purchase Company Common Stock or
Company Preferred Stock (each, a "Company Warrant") shall be assumed by Parent
as more specifically provided in Section 7.9 hereof.


                                       A-2
<PAGE>

     (e) The holders of Dissenting Shares, if any, shall be entitled to payment
by the Surviving Corporation of the appraised value of such shares to the extent
permitted by and in accordance with the provisions of Chapter 13 of the GCL;
provided, however, that (i) if any holder of the Dissenting Shares shall, under
the circumstances permitted by the GCL, subsequently deliver a written
withdrawal of such holder's demand for appraisal of such shares, or (ii) if any
holder fails to establish such holder's entitlement to rights to payment as
provided in such Chapter 13, or (iii) if neither any holder of Dissenting Shares
nor the Surviving Corporation has filed a petition demanding a determination of
the value of all Dissenting Shares within the time provided in such Chapter 13,
such holder or holders (as the case may be) shall forfeit such right to payment
for such shares and such shares shall thereupon be deemed to have been converted
into Parent Common Stock pursuant to Section 3.1(a) as of the Effective Time.
The Surviving Corporation shall be solely responsible for, and shall pay out of
its own funds, any amounts which become due and payable to holders of Dissenting
Shares, and such amounts shall not be paid directly or indirectly by Parent.

     Section 3.2. Exchange of Company Common Stock; Procedures.

     (a) Prior to the Closing Date, Parent shall designate its stock transfer
agent and registrar, or other agent reasonably acceptable to the Company, to act
as Exchange Agent hereunder (the "Exchange Agent"). As soon as practicable after
the Effective Time, Parent shall deposit with or for the account of the Exchange
Agent stock certificates representing the number of shares of Parent Common
Stock issuable pursuant to Section 3.1, which shares of Parent Common Stock
shall be deemed to have been issued at the Effective Time.

     (b) As soon as practicable after the Effective Time, Parent shall cause the
Exchange Agent to mail to each holder of record of a certificate or certificates
which immediately prior to the Effective Time represented outstanding shares of
Company Common Stock, including certificates representing Company Preferred
Stock that was converted into Company Common Stock in connection with the Merger
(the "Certificates") that were converted pursuant to Section 3.1 into the right
to receive shares of Parent Common Stock (i) a form of letter of transmittal
specifying that delivery shall be effected, and risk of loss and title to the
Certificates shall pass, only upon proper delivery of the Certificates to the
Exchange Agent and (ii) instructions for use in surrendering such Certificates
in exchange for certificates representing shares of Parent Common Stock. Upon
surrender of a Certificate for cancellation to the Exchange Agent, together with
such letter of transmittal, duly executed, the holder of such Certificate shall
be entitled to receive in exchange therefor (x) a certificate representing that
number of whole shares of Parent Common Stock which such holder has the right to
receive pursuant to the provisions of this Article III and (y) cash in lieu of
any fractional shares of Parent Common Stock to which such holder is entitled
pursuant to Section 3.4, after giving effect to any required tax withholdings,
and the Certificate so surrendered shall forthwith be canceled. In the event of
a transfer of ownership of Company Common Stock which is not registered in the
transfer records of the Company, a certificate representing the proper number of
shares of Parent Common Stock may be issued to a transferee if the Certificate
representing such Company Common Stock is presented to the Exchange Agent,
accompanied by all documents required to evidence and effect such transfer, and
by evidence that any applicable stock transfer taxes have been paid. Until
surrendered as contemplated by this Section 3.2(b), each Certificate shall be
deemed at any time after the Effective Time to represent only the right to
receive upon such surrender a certificate representing shares of Parent Common
Stock and cash in lieu of any fractional shares of Parent Common Stock as
contemplated by this Article III.

     (c) If any Certificate shall have been lost, stolen or destroyed, the
person in whose name the shares of Company Common Stock represented by such
Certificate are registered on the books of the Company shall be entitled to
receive a certificate representing shares of Parent Common Stock and cash in
lieu of any fractional shares of Parent Common Stock as contemplated by this
Article III upon delivery of a duly executed letter of transmittal and an
appropriate affidavit and, if required by Parent, a bond (in such sum as Parent
may reasonably direct) as indemnity against any claim that may be made against
Parent or the Surviving Corporation with respect to such Certificate.

     Section 3.3. Dividends; Transfer Taxes; Escheat. No dividends or
distributions that are declared on shares of Parent Common Stock will be paid to
persons entitled to receive certificates representing shares of Parent Common
Stock until such persons surrender their Certificates. Upon such surrender,
there shall


                                       A-3
<PAGE>

be paid, to the person in whose name the certificates representing such shares
of Parent Common Stock shall be issued, any dividends or distributions with
respect to such shares of Parent Common Stock which have a record date after the
Effective Time and shall have become payable between the Effective Time and the
time of such surrender. In no event shall the person entitled to receive such
dividends or distributions be entitled to receive interest thereon. Promptly
following the date which is six months after the Effective Time, the Exchange
Agent shall deliver to the Surviving Corporation all cash, certificates and
other documents in its possession relating to the transactions described in this
Agreement, and any holders of Company Common Stock who have not theretofore
complied with this Article III shall look thereafter only to the Surviving
Corporation for the shares of Parent Common Stock, any dividends or
distributions thereon, and any cash in lieu of fractional shares thereof to
which they are entitled pursuant to this Article III. Notwithstanding the
foregoing, neither the Exchange Agent nor any party hereto shall be liable to a
holder of Company Common Stock for any shares of Parent Common Stock, any
dividends or distributions thereon or any cash in lieu of fractional shares
thereof delivered to a public official pursuant to applicable abandoned
property, escheat or similar laws upon the lapse of the applicable time periods
provided for therein.

     Section 3.4. No Fractional Securities. No certificates or scrip
representing fractional shares of Parent Common Stock shall be issued upon the
surrender for exchange of Certificates, and such fractional interests shall not
entitle the owner thereof to vote or to any rights of a security holder. In lieu
of any such fractional securities, each holder of Company Common Stock who would
otherwise have been entitled to a fraction of a share of Parent Common Stock
upon surrender of such holder's Certificates (after aggregating all fractional
shares of Parent Common Stock issuable to such holder) will be entitled to
receive, and Parent will timely provide (or cause to be provided) to the
Exchange Agent sufficient funds to make, a cash payment (without interest)
determined by multiplying (i) the fractional interest to which such holder would
otherwise be entitled (after taking into account all shares of Company Common
Stock then held of record by such holder) and (ii) the average of the per share
closing prices for Parent Common Stock on the Nasdaq National Market ("Nasdaq")
for the five trading days immediately preceding the Effective Time. It is
understood (i) that the payment of cash in lieu of fractional shares of Parent
Common Stock is solely for the purpose of avoiding the expense and inconvenience
to Parent of issuing fractional shares and does not represent separately
bargained-for consideration and (ii) that no holder of Company Common Stock will
receive cash in lieu of fractional shares of Parent Common Stock in an amount
greater than the value of one full share of Parent Common Stock.

     Section 3.5. Closing of Company Transfer Books. At the Effective Time, the
stock transfer books of the Company shall be closed, and no transfer of shares
of Company Common Stock shall thereafter be made on such stock transfer books.
If, after the Effective Time, Certificates are presented to the Surviving
Corporation, they shall be canceled and exchanged as provided in this Article
III.

     Section 3.6. Further Assurances. If, at any time after the Effective Time,
the Surviving Corporation shall consider or be advised that any deeds, bills of
sale, assignments, assurances or any other actions or things are necessary or
desirable to vest, perfect or confirm of record or otherwise in the Surviving
Corporation its right, title or interest in, to or under any of the rights,
properties or assets of either of Sub or the Company acquired or to be acquired
by the Surviving Corporation as a result of, or in connection with, the Merger
or otherwise to carry out this Agreement, the officers of the Surviving
Corporation shall be authorized to execute and deliver, in the name and on
behalf of each of Sub and the Company or otherwise, all such deeds, bills of
sale, assignments and assurances and to take and do, in such names and on such
behalf or otherwise, all such other actions and things as may be necessary or
desirable to vest, perfect or confirm any and all right, title and interest in,
to and under such rights, properties or assets in the Surviving Corporation or
otherwise to carry out the purposes of this Agreement.


                                       A-4
<PAGE>

                                   ARTICLE IV



                 REPRESENTATIONS AND WARRANTIES OF THE COMPANY

     The Company represents and warrants to Parent and Sub as follows:

     Section 4.1. Organization. The Company is a corporation duly organized,
validly existing and in good standing under the laws of the State of California
and has the corporate power to carry on its business as it is now being
conducted or presently proposed to be conducted. The Company is duly qualified
as a foreign corporation to do business, and is in good standing, in each
jurisdiction where the character of its properties owned or held under lease or
the nature of its activities makes such qualification necessary, except where
the failure to be so qualified will not have a Company Material Adverse Effect.
A "Company Material Adverse Effect" means any event or condition (excluding
general economic conditions) that has a material adverse effect, individually or
in the aggregate, on the financial condition, results of operations, business,
assets, liabilities, prospects or properties of the Company or the ability of
the Company to perform any of its material obligations under, or to consummate
the Merger and the other transactions contemplated by, this Agreement. The
Company does not have any Subsidiaries. As used in this Agreement, the term
"Subsidiary" means, with respect to any party, any corporation or other
organization, whether incorporated or unincorporated, of which (x) such party or
any other Subsidiary of such party is a general partner (excluding partnerships,
the general partnership interests of which held by such party or any Subsidiary
of such party do not have a majority of the voting interest in such partnership)
or (y) at least a majority of the securities or other interests having by their
terms ordinary voting power to elect a majority of the board of directors or
others performing similar functions with respect to such corporation or other
organization is directly or indirectly owned or controlled by such party and/or
one or more of its Subsidiaries.

     Section 4.2. Capitalization.

     (a) The authorized capital stock of the Company consists of 37,563,708
shares of Company Common Stock and 24,967,639 shares of Preferred Stock, of
which 2,626,892 shares are designated as Series A Preferred Stock, 2,875,000
shares are designated as Series B Preferred Stock, 8,791,432 shares are
designated as Series C Preferred Stock, 250,000 shares are designated as Series
C-1 Preferred Stock, 225,000 shares are designated as Series C-2 Preferred
Stock, 732,601 shares are designated as Series D Preferred Stock, 6,455,493
shares are designated as Series E Preferred Stock, 2,722,513 shares are
designated as Series F Preferred Stock, and 288,708 shares are designated as
Series F-1 Preferred Stock. As of the date hereof, there are issued and
outstanding 4,874,722 shares of Company Common Stock, 2,626,892 shares of
Company Series A Preferred Stock, 2,875,000 shares of Company Series B Preferred
Stock, 8,791,432 shares of Company Series C Preferred Stock, 732,601 shares of
Company Series D Preferred Stock, 6,455,493 shares of Company Series E Preferred
Stock, 2,722,513 shares of Company Series F Preferred Stock, and 288,708 shares
of Company Series F-1 Preferred Stock. As of the date hereof there are
outstanding (i) Company Stock Options to acquire 3,034,058 shares of Company
Common Stock under all stock option plans of the Company or otherwise, of which
options to acquire 3,034,058 shares of Company Common Stock are exercisable as
of the date hereof, and (ii) Company Warrants to acquire 475,000 shares of
Company Preferred Stock, of which Company Warrants to acquire 400,000 shares of
Company Preferred Stock are exercisable as of the date hereof. 28,001,697 shares
of Company Common Stock are reserved for issuance pursuant to the Company Stock
Options, the Company Warrants and all other Rights (as hereinafter defined) to
purchase or otherwise receive from the Company capital stock or other securities
of the Company. All of the issued and outstanding shares of Company Common Stock
and Company Preferred Stock are validly issued, fully paid and nonassessable.

     (b) Except as set forth on Schedule 4.2(b), (i) there is no outstanding
right, subscription, warrant, call, option or other agreement or arrangement
(including, without limitation, pursuant to any employee benefit plan) of any
kind (collectively, "Rights") to purchase or otherwise to receive from the
Company any of the authorized but unissued or treasury shares of the capital
stock or any other security of the Company or to require the Company to purchase
any such security, (ii) there is no outstanding security


                                       A-5
<PAGE>

of any kind convertible into or exchangeable for such capital stock, and (iii)
there is no voting trust or other agreement or understanding to which the
Company is a party or is bound with respect to the voting of the capital stock
of the Company. The conversion of the Company Stock Options and the Company
Warrants provided for in Section 7.9 of this Agreement is in accordance with the
respective terms of the Company Stock Options and the plans under which they
were issued and the instruments governing the Company Warrants, as the case may
be.

     (c) Since December 31, 1999, except as set forth on Schedule 4.2(c), the
Company has not in any manner accelerated or provided for the acceleration of
the vesting or exercisability of, or otherwise modified the terms and conditions
applicable to, any of the Company Stock Options or the Company Warrants, whether
set forth in the governing stock option plans of the Company, a stock option
grant, award or other agreement or otherwise. Except as set forth on Schedule
4.2(c), none of the awards, grants or other agreements pursuant to which Company
Stock Options or the Company Warrants were issued have provisions which
accelerate the vesting or right to exercise such options or warrants upon the
execution of this Agreement (including the documents attached as Exhibits
hereto), the consummation of the transactions contemplated hereby (or thereby)
or any other "change of control" events.

     Section 4.3. Authority Relative to this Agreement. The Company has the
requisite corporate power and authority to execute and deliver this Agreement
and the Option Agreement and to consummate the transactions contemplated hereby
and thereby. The execution and delivery of this Agreement and the Option
Agreement by the Company and the consummation by the Company of the transactions
contemplated on its part hereby and thereby have been duly authorized by the
Company's Board of Directors and, except for the approval of its shareholders to
be sought at the shareholders meeting contemplated by Section 7.5(a) with
respect to this Agreement, no other corporate proceedings on the part of the
Company are necessary to authorize this Agreement or the Option Agreement or for
the Company to consummate the transactions contemplated hereby or thereby. This
Agreement and the Option Agreement have been duly and validly executed and
delivered by the Company and each constitutes a valid and binding agreement of
the Company, enforceable against the Company in accordance with its terms,
subject to (i) laws of general application relating to bankruptcy, insolvency
and the relief of debtors, and (ii) rules of law governing specific performance,
injunctive relief and other equitable remedies.


     Section 4.4. Consents and Approvals; No Violations. Neither the execution,
delivery and performance of this Agreement or the Option Agreement by the
Company, nor the consummation by the Company of the transactions contemplated
hereby or thereby, will (i) conflict with or result in any breach of any
provisions of the charter, by-laws or other organizational documents of the
Company, (ii) require a filing with, or a permit, authorization, consent or
approval of, any federal, state, local or foreign court, arbitral tribunal,
administrative agency or commission or other governmental or other regulatory
authority or administrative agency or commission (a "Governmental Entity"),
except in connection with or in order to comply with the applicable provisions
of the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the
"HSR Act"), the Securities Act of 1933, as amended (the "Securities Act"), state
securities or "blue sky" laws, and the filing and recordation of an Agreement of
Merger as required by the GCL, (iii) except as set forth on Schedule 4.5, result
in a violation or breach of, or constitute (with or without due notice or lapse
of time or both) a default (or give rise to any right of termination,
cancellation or acceleration) under, or result in the creation of liens,
pledges, security interests, claims, charges or other encumbrances of any kind
whatsoever ("Liens") on any property or asset of the Company pursuant to, any of
the terms, conditions or provisions of any Material Contract (as defined below),
or (iv) violate any law, order, writ, injunction, decree, statute, rule or
regulation of any Governmental Entity applicable to the Company or any of its
properties or assets.

     Section 4.5. Financial Statements. The (a) audited balance sheets of the
Company as of December 31, 1998 and 1999, the related statements of operations,
stockholders' equity, and cash flows for each of the three years in the period
ended December 31, 1999, and (b) unaudited balance sheets of the Company as of
March 31, 1999 and 2000, the related statements of operations, stockholders'
equity, and cash flows for each of the three-month periods ended March 31, 1999
and March 31, 2000 are set forth as Schedule 4.5 hereto (collectively, the
"Financial Statements"). The Financial Statements have been prepared in


                                       A-6
<PAGE>

accordance with generally accepted accounting principles ("GAAP") consistently
applied throughout the periods indicated and fairly present the consolidated
financial position of the Company as at the dates thereof and the results of
operations and cash flows of the Company for each of the periods then ended.
Except as set forth on Schedule 4.5, since January 1, 1997, there has been no
change in any of the significant accounting (including tax accounting) policies,
practices or procedures of the Company.

     Section 4.6. Absence of Certain Changes or Events; Material Contracts.
Except as set forth on Schedule 4.6, since December 31, 1999, (i) the Company
has not conducted its business and operations other than in the ordinary course
of business and consistent with past practices or taken any actions that, if it
had been in effect, would have violated or been inconsistent with the provisions
of Article VI and (ii) other than general economic conditions, there has not
been any fact, event, circumstance or change affecting or relating to the
Company which has had or is reasonably likely to have a Company Material Adverse
Effect. Except as set forth on Schedule 4.6, the transactions contemplated by
this Agreement will not constitute a change of control under or require the
consent from or the giving of notice to a third party pursuant to the terms,
conditions or provisions of any Material Contract (as defined below), or require
any payment to be made under any Contract to which the Company is a party.

     Section 4.7. Litigation. Except as set forth on Schedule 4.7 hereto, there
is no suit, action, proceeding or investigation pending or, to the knowledge of
the Company, threatened against the Company; nor is there any judgment, decree,
injunction, ruling or order of any Governmental Entity outstanding against the
Company.

     Section 4.8. Section Absence of Undisclosed Liabilities. Except for
liabilities or obligations which are accrued or reserved against in the
Financial Statements (or reflected in the notes thereto) or which were incurred
after March 31, 2000 in the ordinary course of business and consistent with past
practice, and except as set forth on Schedule 4.8, the Company does not have any
liabilities or obligations (whether absolute, accrued, contingent or otherwise)
of a nature required by GAAP to be reflected in a balance sheet (or reflected in
the notes thereto) or which would reasonably be expected to have a Company
Material Adverse Effect.

     Section 4.9. No Default. Except as set forth on Schedule 4.9, the Company
is not in default or violation (and no event has occurred which with notice or
the lapse of time or both would constitute a default or violation) of (i) any
term, condition or provision of its charter, by-laws or comparable
organizational documents, (ii) any material term, condition or provision of any
Material Contract (as defined below), or (iii) any term, condition or provision
of any material order, writ, injunction or decree, or any material statute, rule
or regulation, of any Governmental Entity applicable to the Company.

     Section 4.10. Taxes.

     (a) The Company has heretofore delivered or made available to Parent true,
correct and complete copies of the federal, state, local and foreign Tax Returns
(as hereinafter defined) filed by the Company for each of the years ended
December 31, 1998, 1997, 1996, 1995 and 1994 inclusive. Except as set forth on
Schedule 4.10, the Company has duly filed, all material federal, state, local
and foreign income, franchise, sales and other Tax Returns required to be filed
by the Company. All such Tax Returns are true, correct and complete, in all
material respects, and the Company has paid all Taxes (as hereinafter defined)
shown on such Tax Returns and has made adequate provision for payment of all
accrued but unpaid material Taxes anticipated in respect of all periods since
the periods covered by such Tax Returns. Except as set forth on Schedule 4.10,
all material deficiencies assessed as a result of any examination of Tax Returns
of the Company by federal, state, local or foreign tax authorities have been
paid or reserved on the financial statements of the Company in accordance with
GAAP consistently applied, and true, correct and complete copies of all revenue
agent's reports, "30-day letters," or "90-day letters" or similar written
statements proposing or asserting any Tax deficiency against the Company for any
open year have been heretofore delivered to Parent. The Company has heretofore
delivered or will make available to Parent true, correct and complete copies of
all written tax-sharing agreements and written descriptions of all such
unwritten agreements or arrangements to which the Company is a party. Except as
set forth in Schedule 4.10, no material Tax issue has been raised during the
past five years by any federal, state, local or foreign taxing authority which,
if raised with regard to any subsequent period, could reasonably


                                       A-7
<PAGE>

be expected to result in a proposed material Tax deficiency for any such
subsequent period. Except as disclosed in Schedule 4.10 hereof, the Company has
not granted any extension or waiver of the statutory period of limitations
applicable to any claim for any material Taxes. Schedule 4.10 lists the
consolidated federal income tax returns of the Company that have been examined
by and settled with the Internal Revenue Service (the "Service"). Except as set
forth in Schedule 4.10, (i) no consent has been filed under Section 341(f) of
the Code with respect to the Company; (ii) the Company has not participated in,
or cooperated with, an international boycott within the meaning of Section 999
of the Code; and (iii) the Company has not issued or assumed any corporate
acquisition indebtedness, as defined in Section 279(b) of the Code. The Company
has complied (and until the Effective Time will comply) in all material respects
with all applicable laws, rules and regulations relating to the payment and
withholding of Taxes (including, without limitation, withholding of Taxes
pursuant to Sections 1441 and 1442 of the Code or similar provisions under any
foreign laws) and has, within the time and in the manner prescribed by law,
withheld from employee wages and paid over to the proper governmental
authorities all amounts required to be so withheld and paid over under all
applicable laws. Except as disclosed in Schedule 4.10 hereof, there are no
examinations being conducted of the Company's Tax Returns. Except as set foth on
Schedule 4.10, the Company will not be required to include in a taxable period
ending after the Effective Time material income attributable to a prior taxable
period that was not recognized in that prior taxable period or a result of the
installment method of accounting, the cash method of accounting, the completed
contract method of accounting, the long-term contract method of accounting or a
change in accounting method. No jurisdiction in which the Company does not file
Tax Returns has claimed in writing that, or questioned in writing whether, the
Company is obligated to file Tax Returns in that jurisdiction.

     (b) For purposes of this Agreement, the term "Taxes" shall mean all taxes,
charges, fees, levies, duties, imposts or other assessments, including, without
limitation, income, gross receipts, excise, property, sales, use, transfer,
gains, license, payroll, withholding, capital stock and franchise taxes, imposed
by the United States, or any state, local or foreign government or subdivision
or agency thereof, including any interest, penalties or additions thereto. For
purposes of this Agreement, the term "Tax Return" shall mean any report, return
or other information or document required to be supplied to a taxing authority
in connection with Taxes.

     Section 4.11 Title to Properties; Encumbrances. Except as described in the
following sentence, the Company has good, valid and marketable title to, or a
valid leasehold interest in, all of its material properties and assets (real,
personal and mixed, tangible and intangible), including, without limitation, all
the properties and assets reflected in the balance sheet of the Company as of
March 31, 2000 (except for properties and assets disposed of in the ordinary
course of business and consistent with past practices since March 31, 2000).
Except as set forth on Schedule 4.11, none of such properties or assets are
subject to any Liens (whether absolute, accrued, contingent or otherwise),
except (i) Liens for taxes, assessments or other governmental charges not
delinquent or being contested in good faith and by appropriate proceedings and
with respect to which proper reserves have been taken by the Company and have
been duly reflected on its books and records and, with respect to reserves taken
on or prior to March 31, 2000, the Financial Statements ("Proper Reserves");
(ii) deposits or pledges to secure obligations under workmen's compensation,
social security or similar laws, or under unemployment insurance as to which the
Company is not in default; (iii) deposits or pledges to secure bids, tenders,
contracts (other than contracts for the payment of money), leases, statutory
obligations, surety and appeal bonds and other obligations of like nature
arising in the ordinary course of business of the Company; (iv) judgment Liens
listed on Schedule 4.11 that have been stayed or bonded and mechanics',
workmen's, materialmen's or other like liens with respect to obligations which
are not due or which are being contested in good faith by the Company and as to
which they have taken Proper Reserves; and (v) minor imperfections of title and
encumbrances, if any, which are not substantial in amount, do not materially
detract from the value of the property or assets subject thereto and do not
materially impair the operations of any of the Company.


                                       A-8
<PAGE>

     Section 4.12 Intellectual Property .

     (a) Schedule 4.12 sets forth a list of (i) all patents, patent
applications, registered trademarks, trademark applications, registered
copyrights and copyright applications that are owned by the Company and (ii) all
agreements under which the Company is licensed or otherwise permitted, or
licenses or otherwise permits a third party, to use any of the following (each,
an "Intellectual Property Right"): patent, patent application, trademark
(whether registered or unregistered), trademark application, trade name, service
mark (whether registered or unregistered), service mark application, copyright
(whether registered or unregistered), copyright application, trade secret,
know-how, computer software, invention, design, proprietary right or
intellectual property right (collectively, the "Company Intellectual Property").

     (b) (i) The Company directly or indirectly owns, or is licensed or
otherwise possesses valid rights to use, all Company Intellectual Property
(including, without limitation, in connection with potential products under
development by the Company), (ii) no person is challenging the validity or
enforceability of, or to the knowledge of the Company, infringing or otherwise
violating, the Company Intellectual Property, and (iii) the Company is not and
will not be as a result of the execution and delivery of this Agreement or the
performance of its obligations hereunder, infringing or otherwise violating any
Intellectual Property Rights that are owned by any third party (collectively,
"Third Party Intellectual Property Rights").

     (c) The Company Intellectual Property constitutes all the Intellectual
Property Rights necessary for the business of the Company as currently conducted
and as proposed to be conducted.

     (d) All outstanding registrations and applications for Company Intellectual
Property (i) are valid, subsisting, in proper form and enforceable, and have
been duly maintained, including the submission of all necessary filings and fees
in accordance with the legal and administrative requirements of the appropriate
jurisdictions and (ii) have not lapsed, expired or been abandoned, and no
application or registration therefor is the subject of any pending, or, to the
knowledge of the Company, threatened legal or governmental proceeding before any
registration authority in any jurisdiction.

     Section 4.13 Compliance with Applicable Law. Except as set forth on
Schedule 4.13, (i) the Company holds, and is in compliance with the terms of,
all material permits, licenses, exemptions, orders and approvals of all
Governmental Entities necessary for the current and presently proposed conduct
of its business ("Company Permits"), (ii) no fact exists or event has occurred,
and no action or proceeding is pending or, to the Company's knowledge,
threatened, that has a reasonable possibility of resulting in a revocation,
nonrenewal, termination, suspension or other material impairment of any material
Company Permits, (iii) the business of the Company is not being conducted in
violation, in any material respect, of any applicable law, ordinance,
regulation, judgment, decree or order of any Governmental Entity ("Applicable
Law"), and (iv) to the knowledge of the Company, (x) no investigation or review
by any Governmental Entity with respect to the Company is pending or threatened
or has been undertaken within the past six years, and (y) no Governmental Entity
has indicated an intention to conduct the same.

     Section 4.14 Material Contracts. Schedule 4.14 contains a true, complete
and correct list of all Material Contracts (as hereinafter defined) of the
Company, complete and correct copies of which have been provided to Parent.
Except as set forth in Schedule 4.14, all of the Material Contracts are valid,
binding and in full force and effect, and the Company is not in default (nor has
any event occurred that with notice or lapse of time or both would become a
default) of any of its material obligations under any of the Material Contracts.
Except as set forth in Schedule 4.14, to the Company's knowledge, no contracting
party to any Material Contract (other than the Company) is in default (nor has
any event occurred that with notice or lapse of time or both would become a
default) of any of its obligations under any of the Material Contracts. Except
as set forth in Schedule 4.14, no contracting party to any Material Contract has
notified (whether orally or in writing) the Company of its intention to
terminate, cancel or modify such Material Contract or otherwise to reduce or
change its activity thereunder so as to affect adversely the benefits derived,
or currently expected to be derived, by the Company under such Material
Contract. For purposes of this Agreement, "Material Contracts" shall mean any
written, oral or other agreement, contract, subcontract, lease, understanding,
instrument, note, option, warranty, purchase order, license, sublicense,
insurance policy, benefit plan or legally binding commitment or undertaking of
any nature (each, a "Contract") to which the Company is a party or by which the
Company or any of its properties or assets is bound:


                                       A-9
<PAGE>

     (a) relating to the acquisition, transfer, development, sharing or license
of any Company Intellectual Property (except for any Contract pursuant to which
any Company Intellectual Property is licensed to the Company under any third
party software license generally available to the public);

     (b) that provides for indemnification by the Company of any officer,
director, employee or agent of the Company;

     (c) imposing any restriction on the right or ability of the Company (A) to
compete with any other person, (B) to acquire any product or other asset or any
services from any other person or (C) to develop, sell, supply, distribute,
offer, support or service any product or any technology or other asset to or for
any other person;

     (d) relating to any currency hedging;

     (e) containing standstill or similar provisions;

     (f) (A) to which any Governmental Entity is a party or under which any
Governmental Entity has any rights or obligations, or (B) directly or indirectly
benefitting any Governmental Entity;

     (g) requiring that the Company give any notice or provide any information
to any person prior to considering or accepting any proposal, or prior to
entering into any discussions, agreement, arrangement or understanding relating
to any Acquisition Transaction (as defined below);

     (h) that contemplates or involves the payment or delivery of cash or other
consideration in an amount or having a value in excess of $250,000 annually, or
contemplates or involves the performance of services having a value in excess of
$250,000 annually;

     (i) that would be required to be filed as an exhibit to an annual report on
Form 10-K pursuant to Item 601 of Regulation S-K of the SEC; and

     (j) that has had or could reasonably be expected to have a Company Material
Adverse Effect.

     Section 4.15 FDA Matters.

     (a) The Company is in compliance in all material respects with, and current
in the performance of, any obligation arising under any consent decree, consent
agreement, warning letter, Form 483 issued by or entered into with the FDA or
other notice, response or commitment made to the FDA or any comparable state or
Government Entity.

     (b) The Company has disclosed to Parent any warning letters or material
Form 483s or similar notices, or other correspondence relating to the Company's
compliance status under applicable legal requirements from the FDA within the
last three years.

     (c) Neither the Company nor, to the Company's knowledge, any of its
officers, employees or agents has knowingly committed any act, made any
statement, or failed to make any statement, that would reasonably be expected to
provide a basis for the FDA to invoke its policy respecting "Fraud, Untrue
Statements of Material Facts, Bribery, and Illegal Gratuities," set forth in 56
Fed. Reg. 46191 (September 10, 1991) and any amendments thereto.

     (d) The Company has not been convicted of any crime or engaged in any
conduct which could result in debarment under 21 U.S.C. (section) 335a or any
similar state law or regulation.

     (e) There are no proceedings pending with respect to a violation by the
Company of the Food, Drug and Cosmetic Act, FDA regulations adopted thereunder,
the Controlled Substance Act or any other legislation or regulation promulgated
by any other U.S. federal or state Governmental Entity that reasonably might be
expected to result in criminal liability.

     Section 4.16 Information in Disclosure Documents and Registration
Statements. Except as otherwise set forth in this Article IV and Schedule 4.16
hereto, the information contained in the sections entitled "Business" and
"Management's Discussion and Analysis of Financial Condition and Results of
Operations" of the Company's registration statement on Form S-1, as amended (No.
333-30730), filed with the Securities and Exchange Commission ("SEC") does not
contain any untrue statement of a material fact or omit to state any material
fact required to be stated therein or necessary in order to make the statements
therein, in light of


                                      A-10
<PAGE>

the circumstances under which they are made, not misleading. None of the
information to be supplied by the Company for inclusion in (i) the Registration
Statement to be filed with the SEC by Parent on Form S-4 under the Securities
Act for the purpose of registering the shares of Parent Common Stock to be
issued in connection with the Merger (the "Registration Statement") or (ii) the
proxy statement to be distributed in connection with the Company's meeting of
shareholders to vote upon this Agreement (the "Proxy Statement") will, in the
case of the Registration Statement, at the time it becomes effective and at the
Effective Time, or, in the case of the Proxy Statement or any amendments thereof
or supplements thereto, at the time of the mailing of the Proxy Statement and
any amendments or supplements thereto, and at the time of the meeting of
shareholders of the Company to be held in connection with the Merger, contain
any untrue statement of a material fact or omit to state any material fact
required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they are made, not
misleading. The Proxy Statement will comply as to form in all material respects
with the applicable provisions of the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), and the rules and regulations promulgated
thereunder, except that no representation is made by the Company with respect to
statements made therein based on information supplied by Parent or its
representatives for inclusion in the Proxy Statement or with respect to
information concerning Parent or any of its Subsidiaries incorporated by
reference in the Proxy Statement.

     Section 4.17 Employee Benefit Plans; ERISA.

     (a) Schedule 4.17 hereto sets forth a true and complete list of all
"employee benefit plans" within the meaning of Section 3(3) of the Employee
Retirement Income Security Act of 1974, as amended ("ERISA"), and any other
bonus, profit sharing, compensation, pension, severance, deferred compensation,
fringe benefit, insurance, welfare, post-retirement, health, life, stock option,
stock purchase, restricted stock, tuition refund, service award, company car,
scholarship, relocation, disability, accident, sick, vacation, holiday,
termination, unemployment, individual employment, consulting, executive
compensation, incentive, commission, payroll practices, retention, change in
control, noncompetition, and other plans, agreements, policies, trust funds, or
arrangements (whether written or unwritten, insured or self-insured) (1)
established, maintained, sponsored, or contributed to (or with respect to which
any obligation to contribute has been undertaken) by the Company or any entity
that would be deemed a "single employer" with the Company under Section 414(b),
(c), (m), or (o) of the Code or Section 4001 of ERISA (an "ERISA Affiliate") on
behalf of any employee, director or shareholder of the Company (whether current,
former, or retired) or their beneficiaries or (2) with respect to which the
Company or any ERISA Affiliate has or has had any obligation on behalf of any
such employee, director, shareholder or beneficiary (each a "Company Plan" and,
collectively, the "Company Plans"). True and complete copies of each of the
Company Plans and related documents have been delivered to Parent.

     (b) None of the Company, any ERISA Affiliate, or any of their respective
predecessors has ever contributed to, contributes to, has ever been required to
contribute to, or otherwise participated in or participates in or in any way,
directly or indirectly, has any liability with respect to any plan subject to
Section 412 of the Code, Section 302 of ERISA or Title IV of ERISA, including,
without limitation any, "multiemployer plan" (within the meaning of Sections
(3)(37) or 4001(a)(3) of ERISA or Section 414(f) of the Code), or any single
employer pension plan (within the meaning of Section 4001(a)(15) of ERISA) which
is subject to Sections 4063 and 4064 of ERISA.

     (c) With respect to each of the Company Plans: (1) each Company Plan
intended to qualify under Section 401(a) of the Code is qualified and has
received a determination letter from the IRS to the effect that the Company Plan
is qualified under Section 401 of the Code and any trust maintained pursuant
thereto is exempt from federal income taxation under Section 501 of the Code and
nothing has occurred or is expected to occur through the date of the Effective
Time that caused or could cause the loss of such qualification or exemption or
the imposition of any penalty or tax liability; (2) all payments required by any
Company Plan, any collective bargaining agreement or other agreement, or by law
(including, without limitation, all contributions, insurance premiums, or
intercompany charges) with respect to all periods through the date of the
Effective Time shall have been made prior to the Effective Time (on a pro rata
basis where such payments are otherwise discretionary at year end) or provided
for by the


                                      A-11
<PAGE>

Company as applicable, by full accruals as if all targets required by such
Company Plan had been or will be met at maximum levels on its financial
statements; (3) no claim, lawsuit, arbitration or other action relating to any
Company Plan has been threatened, asserted, instituted, or, to the knowledge of
the Company, is anticipated against the Company Plans (other than non-material
routine claims for benefits, and appeals of such claims), any trustee or
fiduciaries thereof, the Company, any ERISA Affiliate, any director, officer, or
employee thereof, or any of the assets of any trust of the Company Plans; (4)
the Company Plan complies and has been maintained and operated in accordance
with its terms and applicable law, including, without limitation, ERISA and the
Code; (5) no "prohibited transaction," within the meaning of Section 4975 of the
Code and Section 406 of ERISA, has occurred or is expected to occur with respect
to the Company Plan (and the consummation of the transactions contemplated by
this Agreement will not constitute or directly or indirectly result in such a
"prohibited transaction"); (6) no Company Plan is or expected to be under audit
or investigation by the Service, U.S. Department of Labor, or any other
governmental authority and no such completed audit, if any, has resulted in the
imposition of any tax or penalty; (7) with respect to each Company Plan that is
funded mostly or partially through an insurance policy, neither the Company nor
any ERISA Affiliate has any liability in the nature of retroactive rate
adjustment, loss sharing arrangement or other actual or contingent liability
arising wholly or partially out of events occurring on or before the Effective
Time.

     (d) Except as set forth in Schedule 4.17, the consummation of the
transactions contemplated by this Agreement will not give rise to any liability,
including, without limitation, liability for severance pay, unemployment
compensation, termination pay, or withdrawal liability, or accelerate the time
of payment or vesting or increase the amount of compensation or benefits due to
any employee, director, or shareholder of the Company (whether current, former,
or retired) or their beneficiaries solely by reason of such transactions or by
reason of a termination following such transactions. No amounts payable under
any Company Plan will fail to be deductible for federal income tax purposes by
virtue of Sections 280G or 162(m) of the Code. Neither the Company nor any ERISA
Affiliate maintains, contributes to, or in any way provides for any benefits of
any kind whatsoever (other than under Section 4980B of the Code, the Federal
Social Security Act, or a plan qualified under Section 401(a) of the Code) to
any current or future retiree or terminee. Neither the Company, any ERISA
Affiliate, nor any officer or employee thereof, has made any promises or
commitments, whether legally binding or not, to create any additional plan,
agreement, or arrangement, or to modify or change any existing Company Plan. No
event, condition, or circumstance exists that could result in an increase of the
benefits provided under any Company Plan or the expense of maintaining any
Company Plan from the level of benefits or expense incurred for the most recent
fiscal year ended before the Effective Time. Neither the Company nor any ERISA
Affiliate has any unfunded liabilities pursuant to any Company Plan that is not
intended to be qualified under Section 401(a) of the Code and is an employee
pension benefit plan within the meaning of Section 3(2) of ERISA, a nonqualified
deferred compensation plan or an excess benefit plan. No event, condition, or
circumstance exists that would prevent the amendment or termination of any
Company Plan.

     Section 4.18 Environmental Laws and Regulations. Except as set forth on
Schedule 4.18(a): (i) the Company is and has been, in all material respects, in
compliance with, and there are no outstanding allegations by any person or
entity that the Company has not been in compliance with, all applicable laws,
rules, regulations, common law, ordinances, decrees, orders or other binding
legal requirements relating to pollution (including the treatment, storage and
disposal of wastes and the remediation of releases and threatened releases of
materials), the preservation of the environment, and the exposure to materials
in the environment or work place ("Environmental Laws") and (ii) the Company
currently holds all permits, licenses, registrations and other governmental
authorizations (including exemptions, waivers, and the like) and financial
assurance required under Environmental Laws for the Company to operate its
businesses as currently conducted.

     (b) Except as set forth on Schedule 4.18(b), (i) there is no friable
asbestos-containing material in or on any real property currently owned, leased
or operated by the Company, and (ii) there are and, to the knowledge of the
Company, have been no underground storage tanks (whether or not required to be
registered under any applicable law), dumps, landfills, lagoons, surface
impoundments, injection wells or other land disposal units in or on any property
currently owned, leased or operated by the Company.


                                      A-12
<PAGE>

     (c) Except as set forth on Schedule 4.18(c), (i) the Company has not
received (x) any written communication from any person stating or alleging that
the Company may be a potentially responsible party under any Environmental Law
(including, without limitation, the Federal Comprehensive Environmental
Response, Compensation, and Liability Act of 1980, as amended) with respect to
any actual or alleged environmental contamination or (y) any request for
information under any Environmental Law from any Governmental Entity with
respect to any actual or alleged material environmental contamination; and (ii)
neither the Company nor any Governmental Entity is conducting or has conducted
(or, to the knowledge of the Company, is threatening to conduct) any
environmental remediation or investigation with respect to the Company or any
real property owned, leased or operated by the Company.

     Section 4.19 Vote Required. The affirmative vote of the holders of (a) a
majority of the outstanding shares of the Company Common Stock,(b) a majority of
the outstanding shares of Company Preferred Stock, are the only votes of the
holders of any class or series of the Company's capital stock necessary to
approve the Merger and (c) 75% of the Company Preferred Stock as a class is
required to approve the conversion of the Company Common Stock into the Company
Preferred Stock. The Board of Directors of the Company, at a meeting duly called
and held on June 28, 2000, unanimously (i) approved this Agreement, the Voting
and Proxy Agreement and the Option Agreement, (ii) determined that the
transactions contemplated hereby and thereby are fair to and in the best
interests of the holders of Company Common Stock and Company Preferred Stock and
(iii) determined to recommend this Agreement, the Merger and the other
transactions contemplated hereby to such holders for approval and adoption. The
resolutions of the Company's Board of Directors taking the actions described in
the preceding sentence have not been rescinded, withdrawn, amended or otherwise
modified, remain in full force and effect, and constitute the only action of
such Board of Directors with respect to the Merger or the other transactions
contemplated by this Agreement.

     Section 4.20 Opinion of Financial Advisor. The Company has received the
opinion of FleetBoston Robertson Stephens Inc., dated June 28, 2000,
substantially to the effect that the Exchange Ratio is fair to the holders of
the Company Common Stock from a financial point of view, a copy of which opinion
has been delivered to Parent.

     Section 4.21 Accounting Matters. None of the Company or, to the Company's
knowledge, any of its directors, officers or stockholders has taken any action
or is aware of any condition which would prevent the accounting for the Merger
as a pooling of interests in accordance with Accounting Principles Board Opinion
No. 16, the interpretative releases pursuant thereto and the pronouncements of
the SEC.

     Section 4.22 Labor Matters. The Company is not a party to, or bound by, any
collective bargaining agreement, contract or other understanding with a labor
union or labor organization, and, to the knowledge of the Company, there is no
activity involving any employees of the Company seeking to certify a collective
bargaining unit or engaging in any other organizational activity.

     Section 4.23 Affiliate Transactions. Except as set forth in Schedule 4.24,
there are no Contracts or other transactions between the Company, on the one
hand, and any (i) officer or director of the Company, (ii) record or beneficial
owner of five percent or more of the voting securities of the Company or (iii)
affiliate (as such term is defined in Regulation 12b-2 promulgated under the
Exchange Act) of any such officer, director or beneficial owner, on the other
hand.

     Section 4.24 Brokers. Except for its financial advisors, Robertson
Stephens, no broker, finder or financial advisor is entitled to any brokerage,
finder's or other fee or commission in connection with the Merger or the
transactions contemplated by this Agreement based upon arrangements made by or
on behalf of the Company, and the Company has delivered to the Parent true,
complete and correct copies of (or, in the case of any oral agreement or
arrangement, a true, complete and correct summary of) each agreement or
arrangement pursuant to which any of such advisors is entitled to any such fee
or commission.

     Section 4.25 Tax Matters. The Company knows of no fact or circumstance
which is reasonably likely to cause the Merger to be treated other than as a
tax-free reorganization under Section 368(a) of the Code.


                                      A-13
<PAGE>

                                    ARTICLE V

            REPRESENTATIONS AND WARRANTIES OF PARENT AND MERGER SUB


     Parent and Merger Sub represent and warrant to the Company as follows:


     Section 5.1 Organization. Parent is a corporation duly organized, validly
existing and in good standing under the laws of the State of Delaware and has
the corporate power to carry on its business as it is now being conducted or
presently proposed to be conducted. Parent is duly qualified as a foreign
corporation to do business, and is in good standing, in each jurisdiction where
the character of its properties owned or held under lease or the nature of its
activities make such qualification necessary, except where the failure to be so
qualified will not have a Parent Material Adverse Effect. A "Parent Material
Adverse Effect" means any event or condition (excluding general economic
conditions) that has a material adverse effect individually or in the aggregate,
on the financial condition, results of operations, business, assets,
liabilities, prospects or properties of Parent and its Subsidiaries taken as a
whole or on the ability of Parent to perform any of its material obligations
under, or to consummate the Merger and the other transactions contemplated by
this Agreement. Sub is a corporation duly organized, validly existing and in
good standing under the laws of the State of California. Sub has not engaged in
any business (other than in connection with this Agreement and the transactions
contemplated hereby) since the date of its incorporation.


     Section 5.2 Capitalization.


     (a) The authorized capital stock of Parent consists of 120,000,000 shares
of Parent Common Stock and 5,000,000 shares of Preferred Stock, par value $.01
per share, of Parent ("Parent Preferred Stock"). As of June 27, 2000, (i) based
on information provided by Parent's transfer agent, 65,743,753 shares of Parent
Common Stock are issued and outstanding, (ii) no shares of Parent Preferred
Stock are issued and outstanding, (iii) options to acquire 7,227,670 shares of
Parent Common Stock (the "Parent Stock Options") are outstanding under all stock
option plans of Parent, and (iv) 10,139,826 shares of Parent Common Stock are
reserved for issuance pursuant to the Parent Stock Options and all other Rights
to purchase or otherwise receive from Parent capital stock or other securities
of Parent. All of the outstanding shares of capital stock of Parent are, and the
shares of Parent Common Stock issuable in the Merger in accordance with this
Agreement (including, without limitation, shares of Parent Common Stock issuable
upon exercise of Converted Options and Converted Warrants) will be, when so
issued, duly authorized, validly issued, fully paid and nonassessable.


     (b) The authorized capital stock of Sub consists of 1,000 shares of Sub
Common Stock, of which 1,000 shares, as of the date hereof, were issued and
outstanding. All of such outstanding shares are owned by Parent and are validly
issued, fully paid and nonassessable.


     (c) Except as disclosed in Schedule 5.2, (i) there are no outstanding
Rights to purchase or otherwise to receive from Parent or Sub any of the
outstanding authorized but unissued or treasury shares of the capital stock or
any other security of Parent or Sub, (ii) there is no outstanding security of
any kind convertible into or exchangeable for such capital stock, and (iii)
there is no voting trust or other agreement or understanding to which Parent or
Sub is a party or is bound with respect to the voting of the capital stock of
Parent or Sub.


     Section 5.3 Authority Relative to this Agreement. Each of Parent and Sub
has the requisite corporate power and authority to execute and deliver this
Agreement and the Option Agreement and to consummate the transactions
contemplated hereby and thereby. The execution and delivery of this Agreement
and the Option Agreement by each of Parent and Sub and the consummation by
Parent and Sub of the transactions contemplated on its part hereby and thereby
have been duly authorized by their respective Boards of Directors, and by Parent
as the sole stockholder of Sub, and no other corporate proceedings on the part
of Parent or Sub are necessary to authorize this Agreement or the Option
Agreement or for Parent and Sub to consummate the transactions contemplated
hereby or thereby. This Agreement and the Option Agreement each have been duly
and validly executed and delivered by each of Parent and Sub and constitutes a
valid and binding agreement of each of Parent and Sub, enforceable


                                      A-14
<PAGE>

against Parent and Sub in accordance with its terms, subject to (i) laws of
general application relating to bankruptcy, insolvency and the relief of
debtors, and (ii) rules of law governing specific performance, injunctive relief
and other equitable remedies.

     Section 5.4 Consents and Approvals; No Violations. Neither the execution,
delivery and performance of this Agreement or the Option Agreement by Parent or
Sub, nor the consummation by Parent or Sub of the transactions contemplated
hereby or thereby will (i) conflict with or result in any breach of any
provisions of the Certificate of Incorporation or By-Laws of Parent or of Sub,
(ii) require a filing with, or a permit, authorization, consent or approval of,
any Governmental Entity except in connection with or in order to comply with the
applicable provisions of the HSR Act, the Securities Act, the Exchange Act,
state securities or "blue sky" laws, and the filing and recordation of an
Agreement of Merger as required by the GCL, (iii) except as set forth on
Schedule 5.4 hereto, result in a violation or breach of, or constitute (with or
without due notice or lapse of time or both) a default (or give rise to any
right of termination, cancellation or acceleration) under, or result in the
creation of a Lien on any property or asset of Parent or any of its Subsidiaries
pursuant to, any of the terms, conditions or provisions of any material Contract
to which Parent or Sub is a party or by which either of them or any of their
properties or assets may be bound or (iv) violate any law, order, writ,
injunction, decree, statute, rule or regulation of any Governmental Entity
applicable to Parent, Sub or any of their properties or assets.

     Section 5.5 Reports and Financial Statements. Parent has timely filed all
reports required to be filed with the SEC pursuant to the Exchange Act or the
Securities Act since December 31, 1997 (collectively, the "Parent SEC Reports"),
and has previously made available to the Company true and complete copies of all
such Parent SEC Reports. Such Parent SEC Reports, as of their respective dates,
complied in all material respects with the applicable requirements of the
Securities Act and the Exchange Act, as the case may be, and none of such SEC
Reports contained any untrue statement of a material fact or omitted to state a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading. The financial statements of Parent included in the Parent SEC
Reports have been prepared in accordance with GAAP consistently applied
throughout the periods indicated (except as otherwise noted therein) and fairly
present the consolidated financial position of Parent and its consolidated
Subsidiaries as at the dates thereof and the consolidated results of operations
and cash flows of Parent and its consolidated Subsidiaries for each of the
periods then ended, except that in the case of the unaudited consolidated
financial statements included in any Form 10-Q, the presentation and disclosures
conform with the applicable rules of the Exchange Act, but include all
adjustments necessary to conform to GAAP requirements with respect to interim
financial statements. Since December 31, 1997, there has been no change in any
of the significant accounting (including tax accounting) policies, practices or
procedures of the Parent or, except as set forth on Schedule 5.5, any of its
consolidated Subsidiaries.

     Section 5.6 Absence of Certain Changes or Events. Except as set forth in
the Parent SEC Reports, since March 31, 2000, (i) Parent has not conducted its
business and operations other than in the ordinary course of business and
consistent with past practices and (ii) there has not been any fact, event,
circumstance or change affecting or relating to Parent and its Subsidiaries
which has had or is reasonably likely to have a Parent Material Adverse Effect.


     Section 5.7 Information in Disclosure Documents and Registration Statement.
None of the information to be supplied by Parent or Sub for inclusion in (i) the
Registration Statement or (ii) the Proxy Statement will in the case of the
Registration Statement, at the time it becomes effective and at the Effective
Time, or, in the case of the Proxy Statement or any amendments thereof or
supplements thereto, at the time of the mailing of the Proxy Statement and any
amendments or supplements thereto, and at the time of the meeting of
stockholders of the Company to be held in connection with the Merger, contain
any untrue statement of a material fact or omit to state any material fact
required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they are made, not
misleading. The Registration Statement will comply as to form in all material
respects with the applicable provisions of the Securities Act and the Exchange
Act, and the rules and regulations promulgated thereunder, except that no
representation is made by Parent with respect to statements


                                      A-15
<PAGE>

made therein based on information supplied by the Company or its representatives
for inclusion in the Registration Statement or the Proxy Statement.

     Section 5.8 Compliance with Applicable Law. Except as set forth on Schedule
5.8 or as disclosed in the Parent SEC Reports, (i) the Parent and its
Subsidiaries hold, and are in compliance with the terms of, all material
permits, licenses, exemptions, orders and approvals of all Governmental Entities
necessary for the current and presently proposed conduct of their respective
businesses ("Parent Permits"), (ii) no fact exists or event has occurred, and no
action or proceeding is pending or, to Parent's knowledge, threatened, that has
a reasonable possibility of resulting in a revocation, nonrenewal, termination,
suspension or other material impairment of any material Parent Permits, (iii)
the businesses of Parent and its Subsidiaries are not being conducted in
violation of Applicable Law, and (iv) to the knowledge of Parent, (x) no
investigation or review by any Governmental Entity with respect to Parent or its
Subsidiaries is pending or threatened and (y) no Governmental Entity has
indicated an intention to conduct the same.

     Section 5.9 Litigation. There is no suit, action, proceeding or
investigation pending or, to the knowledge of Parent, threatened against or
affecting Parent or any of its Subsidiaries, the outcome of which, in the
reasonable judgment of Parent, is likely to have a Parent Material Adverse
Effect; nor is there any judgment, decree, injunction, ruling or order of any
Governmental Entity outstanding against Parent or any of its Subsidiaries
having, or which is reasonably likely to have, a Parent Material Adverse Effect.

     Section 5.10 Opinion of Financial Advisor. Parent has received the opinion
of Prudential Securities, dated June 28, 2000, substantially to the effect that
the Exchange Ratio is fair to the holders of Parent Common Stock from a
financial point of view, a copy of which opinion has been delivered to the
Company.

     Section 5.11 Accounting Matters. None of the Parent, any of its
Subsidiaries or, to Parent's knowledge, any of their respective directors,
officers or stockholders has taken any action or is aware of any condition which
would prevent the accounting for the Merger as a pooling of interests in
accordance with Accounting Principles Board Opinion No. 16, the interpretative
releases pursuant thereto and the pronouncements of the SEC.

     Section 5.12 Tax Matters. Parent knows of no fact or circumstance which is
reasonably likely to cause the Merger to be treated other than as a tax-free
reorganization under Section 368(a) of the Code.

     Section 5.13 Brokers. Except for its financial advisor, Prudential
Securities, no broker, finder or financial advisor is entitled to any brokerage,
finder's or other fee or commission in connection with the Merger or the
transactions contemplated by this Agreement based upon arrangements made by or
on behalf of Parent or Sub.



                                  ARTICLE VI
                CONDUCT OF COMPANY BUSINESS PENDING THE MERGER

     From the date of this Agreement until the earlier of the Effective Time or
the termination of this Agreement, unless Parent shall otherwise agree in
writing, or as otherwise expressly contemplated by this Agreement:

     (a) the Company shall conduct its business only in the ordinary and usual
course consistent with past practice, and the Company shall use its reasonable
efforts to preserve intact the present business organization, keep available the
services of its present officers and key employees, and preserve the goodwill of
those having business relationships with it;

     (b) the Company shall not (i) amend its charter, bylaws or other
organizational documents, (ii) split, combine or reclassify any shares of its
outstanding capital stock, (iii) declare, set aside or pay any dividend or other
distribution payable in cash, stock or property, or (iv) directly or indirectly
redeem or otherwise acquire any shares of its capital stock;


                                      A-16
<PAGE>

     (c) the Company shall not, (i) authorize for issuance, issue or sell or
agree to issue or sell any shares of, or Rights to acquire or convertible into
any shares of, its capital stock (whether through the issuance or granting of
options, warrants, commitments, subscriptions, rights to purchase or otherwise),
except for the issuance of shares of Company Common Stock upon the exercise of
Company Stock Options outstanding on the date of this Agreement, or amend any
outstanding Company Stock Option, Company Warrant or other Right; (ii) merge or
consolidate with another entity; (iii) acquire or purchase an equity interest in
or a substantial portion of the assets of another corporation, partnership or
other business organization or otherwise acquire any assets outside the ordinary
and usual course of business and consistent with past practice or otherwise
enter into any material Contract, commitment or transaction outside the ordinary
and usual course of business consistent with past practice; (iv) sell, lease,
license, waive, release, transfer, encumber or otherwise dispose of any of its
material assets; (v) incur, assume or prepay any material indebtedness or any
other material liabilities other than in the ordinary course of business and
consistent with past practice and other than in connection with borrowing up to
$2 million under a secured line of credit with MMC/GATX Partnership No. I; (vi)
assume, guarantee, endorse or otherwise become liable or responsible (whether
directly, contingently or otherwise) for the obligations of any other person
other than customers, in each case in the ordinary course of business and
consistent with past practice; (vii) make, extend or modify in any material
respect any loans, advances or capital contributions to, or investments in, any
other person; (viii) authorize or make capital expenditures in excess of the
respective amounts set forth on Schedule 6 hereto; (ix) permit any insurance
policy naming the Company as a beneficiary or a loss payee to be canceled or
terminated other than in the ordinary course of business; (x) form any
Subsidiary; or (xi) enter into any contract, agreement, commitment or
arrangement with respect to any of the foregoing;

     (d) the Company shall not (i) adopt, enter into, terminate or amend (except
as may be required by Applicable Law) any Company Plan or other arrangement for
the current or future benefit or welfare of any director, officer or current or
former employee, (ii) increase in any manner the compensation or fringe benefits
of, or pay any bonus to, any director, officer or employee (except for normal
increases in compensation in the ordinary course of business consistent with
past practice and accrued and unpaid bonuses in respect of the Company's fiscal
year ended December 31, 1999 that are consistent with past practice and have
been properly accrued and reflected on the Company's books and records), or
(iii) take any action to fund or in any other way secure, or to accelerate or
otherwise remove restrictions with respect to, the payment of compensation or
benefits under any employee plan, agreement, contract, arrangement or other
Company Plan (including the Company Stock Options);

     (e) the Company shall not take any action with respect to, or make any
material change in, its accounting or tax policies or procedures, except as
required by law or to comply with GAAP; and

     (f) the Company shall not (i) take any action or allow any action to be
taken by any of its affiliates which would jeopardize the treatment of Parent's
acquisition of the Company as a pooling of interests for accounting purposes; or
(ii) take any action which would jeopardize qualification of the Merger as a
reorganization within the meaning of Section 368(a) of the Code.


                                      A-17
<PAGE>

                                   ARTICLE VII

                              ADDITIONAL AGREEMENTS

     Section 7.1 Access and Information. Each of the Company and Parent shall
(and shall cause its Subsidiaries and its and their respective officers,
directors, employees, auditors and agents to) afford to the other and to the
other's officers, employees, financial advisors, legal counsel, accountants,
consultants and other representatives reasonable access, during normal business
hours throughout the period from the date hereof until the earlier of the
Effective Time and the termination of this Agreement, to all of its books and
records and its properties, plants and personnel and, during such period, each
shall furnish promptly to the other a copy of each report, schedule and other
document filed or received by it pursuant to the requirements of federal
securities laws, provided that no investigation pursuant to this Section 7.1
shall affect any representations or warranties made herein or the conditions to
the obligations of the respective parties to consummate the Merger. Unless
otherwise required by law, each of Parent and the Company agrees that it (and
its respective Subsidiaries and its and their respective representatives) shall
hold in confidence all non-public information so acquired in accordance with the
terms of the confidentiality agreement between Parent and the Company executed
May 25, 2000 (the "Confidentiality Agreement").


     Section 7.2 No Solicitation. Prior to the Effective Time, the Company
agrees that neither it, any of its affiliates, nor any of the respective
directors, officers, employees, affiliates, agents or representatives of the
foregoing (including, without limitation, any investment banker, attorney or
accountant retained by the Company) will, directly or indirectly, solicit,
initiate, facilitate or encourage (including by way of furnishing or disclosing
non-public information) any inquiries or the making of any proposal with respect
to or which may reasonably be expected to lead to, any merger, consolidation or
other business combination involving the Company or the acquisition of all or
any significant portion of the assets or capital stock of the Company, other
than the Merger (an "Acquisition Transaction") or negotiate, explore or
otherwise engage in discussions with any corporation, partnership, person, other
entity or group (as defined in Section 13(d)(2) of the Exchange Act) (other than
Parent and its representatives) in furtherance of such inquiries or with respect
to any Acquisition Transaction, or endorse any Acquisition Transaction, or enter
into any agreement, arrangement or understanding with respect to any such
Acquisition Transaction or which would require it to abandon, terminate or fail
to consummate the Merger or any other transaction contemplated by this
Agreement. The Company agrees that as of the date hereof, it, its affiliates,
and the respective directors, officers, employees, agents and representatives of
the foregoing, shall immediately cease and cause to be terminated any existing
activities, discussions or negotiations with any person (other than Parent and
its representatives) conducted heretofore with respect to any Acquisition
Transaction. The Company agrees to immediately advise Parent in writing of any
inquiries or proposals (or desire to make a proposal) received by (or indicated
to), any such information requested from, or any such negotiations or
discussions sought to be initiated or continued with, any of it, its affiliates,
or any of the respective directors, officers, employees, agents or
representatives of the foregoing, in each case from a corporation, partnership,
person or other entity or group (other than Parent and its representatives) with
respect to an Acquisition Transaction, and the terms thereof, including the
identity of such third party, and to update on an ongoing basis or upon Parent's
request, the status thereof, as well as any actions taken or other developments
pursuant to this Section 7.2(a).


     Section 7.3 Registration Statement. As promptly as practicable, Parent
shall in consultation with the Company, prepare and file with the SEC the Proxy
Statement and the Registration Statement. Parent shall use its reasonable best
efforts to have the Registration Statement declared effective as soon as
practicable. Parent shall also use its reasonable best efforts to take any
action required to be taken under state securities or "blue sky" laws in
connection with the issuance of the shares of Parent Common Stock pursuant to
this Agreement in the Merger. The Company shall furnish Parent with all
information concerning the Company and the holders of its capital stock and
shall take such other action as Parent may reasonably request in connection with
the Registration Statement and the issuance of shares of Parent Common Stock. If
at any time prior to the Effective Time any event or circumstance relating to
Parent, any Subsidiary of Parent, the Company or their respective officers or
directors, should be


                                      A-18
<PAGE>

discovered by such party which should be set forth in an amendment or a
supplement to the Registration Statement or Proxy Statement, such party shall
promptly inform the other thereof and take appropriate action in respect
thereof. As part of the Registration Statement, Parent shall include a reoffer
prospectus to enable resales of Parent Common Stock by holders of Parent Common
Stock who are not Affiliates (as defined in Section 7.6) and have executed and
delivered a Voting and Proxy Agreement.

     Section 7.4 Tax Matters. At or prior to the filing of the Form S-4
Registration Statement, the Parent, Merger Sub and the Company shall execute and
deliver to Proskauer Rose LLP and to Cooley Godward LLP tax representation
letters substantially in the form of Exhibit B hereto. Parent, Merger Sub and
the Company shall each confirm to Proskauer Rose LLP and to Cooley Godward LLP
the accuracy and completeness as of the Effective Time of the tax representation
letters delivered pursuant to the immediately preceding sentence. Parent and the
Company shall use all reasonable efforts prior to and following the Effective
Time to cause the Merger to qualify as a tax free reorganization under Section
368(a) of the Code. Following delivery of the tax representation letters
pursuant to the first sentence of this Section 7.4, each of Parent and the
Company shall use its reasonable efforts to cause Proskauer Rose LLP and Cooley
Godward LLP, respectively, to deliver to it a tax opinion satisfying the
requirements of Item 601 of Regulation S-K promulgated under the Securities Act.
In rendering such opinions, each of such counsel shall be entitled to rely on
the tax representation letters referred to in this Section 7.4.

     Section 7.5 Proxy Statements; Stockholder Approval.

     (a) The Company, acting through its Board of Directors, shall, subject to
and in accordance with applicable law and its Articles of Incorporation and
Bylaws, (i) promptly and duly call, give notice of and, as soon as practicable
following the date upon which the Registration Statement becomes effective, hold
a meeting of the holders of Company Common Stock and the holders of Company
Preferred Stock for the purpose of voting to (x) approve the principal terms of
the Merger, (y) adopt and approve the Merger, and (z) approve the conversion of
all outstanding shares of Company Preferred Stock, with such conversion to be
effective immediately prior to the Effective Time and subject to the Effective
Time occurring, (ii) recommend to the shareholders of the Company that they vote
in favor of the matters described in the preceding clause (i), (iii) include in
the Proxy Statement such recommendation and (iv) take all reasonable and lawful
action to solicit and obtain such vote in favor of the matters described in
clause (i) above.

     (b) The Company, as promptly as practicable, shall cause the definitive
Proxy Statement to be mailed to its shareholders.

     (c) At or prior to the Closing, the Company shall deliver to Parent a
certificate of its Secretary setting forth the voting results from its
shareholder meeting.

     Section 7.6 Compliance with the Securities Act.

     (a) At least 10 days prior to the Effective Time, the Company shall cause
to be delivered to Parent a list identifying all persons who were at the record
date for its shareholders' meeting convened in accordance with Section 7.5
hereof, "affiliates" of the Company, as that term is used in paragraphs (c) and
(d) of Rule 145 under the Securities Act (the "Affiliates").

     (b) The Company shall use its reasonable best efforts to cause each person
who is identified as one of its Affiliates in its list referred to in Section
7.6(a) above to deliver to Parent (with a copy to the Company), at least 10 days
prior to the Effective Time, a written agreement, in the form attached hereto as
Exhibit C (the "Affiliate Agreement").

     (c) If any Affiliate of the Company refuses to provide an Affiliate
Agreement, Parent may place appropriate legends on the certificates evidencing
the shares of Parent Common Stock to be received by such Affiliate pursuant to
the terms of this Agreement and may issue appropriate stop transfer instructions
to the transfer agent for shares of Parent Common Stock to the effect that the
shares of Parent Common Stock received by such Affiliate pursuant to this
Agreement only may be sold, transferred or otherwise conveyed (i) pursuant to an
effective registration statement under the Securities Act, (ii) in compliance
with Rule 145 promulgated under the Securities Act, or (iii) pursuant to another
exemption under the Securities Act.


                                      A-19
<PAGE>

     Section 7.7 Reasonable Best Efforts. Subject to the terms and conditions
herein provided, each of the parties hereto agrees to use its reasonable best
efforts to take, or cause to be taken, all action and to do, or cause to be
done, all things necessary, proper or advisable under applicable laws and
regulations to consummate and make effective the transactions contemplated by
this Agreement, including, without limitation, the obtaining of all necessary
waivers, consents and approvals and the effecting of all necessary registrations
and filings. Without limiting the generality of the foregoing, as promptly as
practicable, the Company, Parent and Sub shall make all filings and submissions
under the HSR Act as may be reasonably required to be made in connection with
this Agreement and the transactions contemplated hereby. Subject to the
Confidentiality Agreement, the Company will furnish to Parent and Sub, and
Parent and Sub will furnish to the Company, such information and assistance as
the other may reasonably request in connection with the preparation of any such
filings or submissions. Subject to the Confidentiality Agreement, the Company
will provide Parent and Sub, and Parent and Sub will provide the Company, with
copies of all material written correspondence, filings and communications (or
memoranda setting forth the substance thereof) between such party or any of its
representatives and any Governmental Entity, with respect to the obtaining of
any waivers, consent or approvals and the making of any registrations or
filings, in each case that is necessary to consummate the Merger and the other
transactions contemplated hereby. In case at any time after the Effective Time
any further action is necessary or desirable to carry out the purposes of this
Agreement, the proper officers or directors of Parent and the Surviving
Corporation shall take all such necessary action.


     Section 7.8 Voting and Proxy Agreement; Option Agreement. Concurrently
herewith, and as an essential inducement for Parent's entering into this
Agreement, Parent is entering into the (a) Voting and Proxy Agreement with
certain holders of Company Common Stock with respect to all such shares of
Company Common Stock held by such holders and (b) Option Agreement with the
Company. Parent shall exercise its rights under the Voting and Proxy Agreement
to vote all such shares in the manner provided in the Voting and Proxy
Agreement.


     Section 7.9 Company Stock Options. To the extent permitted by the
respective terms of the Company Stock Options and the plans under which they
were issued and the respective terms of the Company Warrants, at the Effective
Time, each of the Company Stock Options (and, solely with respect to such
options, the applicable option plans pursuant to which such options were issued)
and each of the Company Warrants which is outstanding immediately prior to the
Effective Time shall be assumed by Parent on the terms set forth herein and
converted automatically into an option or a warrant, as the case may be, to
purchase shares of Parent Common Stock (each, a "Converted Option" or a
"Converted Warrant," as the case may be) in an amount and at an exercise price
determined as provided below:


     (a) The number of shares of Parent Common Stock to be subject to a
Converted Option or a Converted Warrant shall be equal to the product of the
number of shares of Company Common Stock or Company Preferred Stock remaining
subject (as of immediately prior to the Effective Time) to the original option
or warrant and the Exchange Ratio, provided that any fractional shares of Parent
Common Stock resulting from such multiplication shall be rounded down to the
nearest share; and


     (b) The exercise price per share of Parent Common Stock under a Converted
Option or a Converted Warrant shall be equal to the exercise price per share of
Company Common Stock or Company Preferred Stock under the original option or
warrant divided by the Exchange Ratio, provided that such exercise price shall
be rounded up to the nearest cent.


     The adjustment provided herein with respect to any options which are
"incentive stock options" (as defined in Section 422 of the Code) shall be
modified to the extent required to comply with Section 424(a) of the Code and
the applicable Treasury Regulations. After the Effective Time, each Converted
Option shall be exercisable and shall vest upon the same terms and conditions as
were applicable to the related Company Stock Option immediately prior to the
Effective Time, except that all references to the Company shall be deemed to be
references to Parent. Parent shall file with the SEC a registration statement on
Form S-8 (or other appropriate form) as soon as practicable (and in any event
within thirty (30) business days) after the Closing Date and shall take any
action required to be taken under state securities "blue sky" laws for purposes
of registering all shares of Parent Common Stock issuable after


                                      A-20
<PAGE>

the Effective Time upon exercise of the Converted Options, and use all
reasonable efforts to have such registration statement (or a successor or
replacement registration statement) become effective with respect thereto as
promptly as practicable after the Effective Time and to remain in effect while
any of the Converted Options remain exercisable. Following the Closing, Parent
will send to each holder of a Converted Option or Converted Warrant a written
notice setting forth (i) the number of shares of Parent Common Stock subject to
such Converted Option or Converted Warrant and (ii) the exercise price per share
of Parent Common Stock issuable upon exercise of such Converted Option or
Converted Warrant. Promptly following the Closing, Parent shall reserve for
issuance in connection with the exercise of Converted Options and Converted
Warrants such number of shares of Parent Common Stock as shall be required to be
issued upon such exercise.

     Section 7.10 Public Announcements. Each of Parent, Sub and the Company
agrees that it will not issue any press release or otherwise make any public
statement with respect to this Agreement (including the Exhibits hereto) or the
transactions contemplated hereby (or thereby) without the prior consent of the
other party, which consent shall not be unreasonably withheld or delayed;
provided, however, that such disclosure can be made without obtaining such prior
consent if (i) the disclosure is required by law or by obligations imposed
pursuant to any listing agreement with any national securities exchange or
quotation system and (ii) the party making such disclosure has first used its
reasonable best efforts to consult with (but not obtain the consent of) the
other party about the form and substance of such disclosure.

     Section 7.11 Expenses. Except as otherwise set forth in Section 9.2,
whether or not the Merger is consummated, all costs and expenses incurred in
connection with this Agreement (including the Exhibits hereto) and the
transactions contemplated hereby (and thereby) shall be paid by the party
incurring such expenses, except that (i) the filing fee in connection with
filings under the HSR Act, (ii) the expenses incurred in connection with
printing the Registration Statement and the Proxy Statement and (iii) the filing
fee with the SEC relating to the Registration Statement or the Proxy Statement
will be paid by Parent.

     Section 7.12 Listing Application. Parent will use its reasonable best
efforts to cause the shares of Parent Common Stock to be issued pursuant to this
Agreement in the Merger (as well as the shares of Parent Common Stock issuable
after the Effective Time upon exercise of the Converted Options and Converted
Warrants) to be listed for quotation and trading on the Nasdaq National Market.

     Section 7.13 Supplemental Disclosure. The Company shall give prompt notice
to Parent, and Parent shall give prompt notice to the Company, of (i) the
occurrence, or non-occurrence, of any event the occurrence, or non-occurrence,
of which would be likely to cause (x) any representation or warranty contained
in this Agreement to be untrue or inaccurate or (y) any covenant, condition or
agreement contained in this Agreement not to be complied with or satisfied and
(ii) any failure of the Company or Parent, as the case may be, to comply with or
satisfy any covenant, condition or agreement to be complied with or satisfied by
it hereunder; provided, however, that the delivery of any notice pursuant to
this Section 7.13 shall not have any effect for the purpose of determining the
satisfaction of the conditions set forth in Article VIII of this Agreement or
otherwise limit or affect the remedies available hereunder to any party.

     Section 7.14 Letters of Accountants.

     (a) Parent shall use reasonable best efforts to cause to be delivered to
the Company a letter of KPMG LLP, Parent's independent auditors, dated a date
within two business days before the date on which the Registration Statement
shall become effective and addressed to the Company, in form and substance
reasonably satisfactory to the Company and customary in scope and substance for
letters delivered by independent public accountants in connection with
registration statements similar to the Registration Statement, which letter
shall be brought down to a date within two business days prior to the Effective
Time.

     (b) The Company shall use reasonable best efforts to cause to be delivered
to Parent a letter of Ernst & Young LLP, the Company's independent auditors,
dated a date within two business days before the date on which the Registration
Statement shall become effective and addressed to Parent, in form and


                                      A-21
<PAGE>

substance reasonably satisfactory to Parent and customary in scope and substance
for letters delivered by independent public accountants in connection with
registration statements similar to the Registration Statement, which letter
shall be brought down to a date within two business days prior to the Effective
Time.

     Section 7.15 Indemnification.

     (a) For a period of six years after the Effective Time, Parent shall cause
the Surviving Corporation to, indemnify, defend and hold harmless the present
and former directors, officers, employees and agents of the Company (each, an
"Indemnified Party") against any and all losses, costs, damages, claims and
liabilities (including reasonable attorneys' fees) arising out of the
Indemnified Party's service or services as a director, officer, employee or
agent of the Company or, if at the Company's request, of another corporation,
partnership, joint venture, trust or other enterprise occurring at or prior to
the Effective Time (including the transactions contemplated by or related to
this Agreement) to the fullest extent permitted under the Company's Articles of
Incorporation and Bylaws as in effect on the date hereof, including provisions
relating to advances of expenses incurred in the defense of any litigation,
action, claim or proceeding and whether or not Surviving Corporation is insured
against any such matter.

     (b) The provisions of this Section 7.15 are intended to be for the benefit
of and shall be enforceable by, each Indemnified Party and his or her respective
heirs and representatives.

     Section 7.16. Other Agreements. Prior to the Effective Time, the Company
will use its best efforts (a) to enter into consulting agreements with each of
the Company's non-employee directors on terms reasonably acceptable to Parent
and (b) terminate, effective as of the Effective Time, any and all provisions of
agreements with the Company's stockholders which give stockholders rights to
consult with and advise management of the Company on significant business
issues, examine the books and records of the Company (except as required by
applicable law), attend meetings of the Company's board of directors and submit
proposals or suggestions to management of the Company, other than in connection
with any collaboration agreements between the Company and the Company's
stockholders.



                                  ARTICLE VIII

                   CONDITIONS TO CONSUMMATION OF THE MERGER

     Section 8.1 Conditions to Each Party's Obligation to Effect the Merger. The
respective obligations of each party to effect the Merger shall be subject to
the satisfaction at or prior to the Effective Time of the following conditions:

     (a) HSR Approval. Any waiting period applicable to the consummation of the
Merger under the HSR Act shall have expired or been terminated, and no action
shall have been instituted by the Department of Justice or Federal Trade
Commission challenging or seeking to enjoin the consummation of this
transaction, which action shall have not been withdrawn or terminated.

     (b) Stockholder Approvals. This Agreement and the transactions contemplated
hereby shall have been approved and adopted by the requisite vote (as described
in Section 4.19) of the shareholders of the Company, in accordance with
applicable law.

     (c) Nasdaq Listing. The shares of Parent Common Stock issuable to the
holders of Company Common Stock pursuant to this Agreement in the Merger or upon
exercise of Converted Options and Converted Warrants shall have been authorized
for listing on the Nasdaq National Market, upon official notice of issuance.

     (d) Registration Statement. The Registration Statement shall have become
effective under the Securities Act and shall not be the subject of any stop
order or proceeding by the SEC seeking a stop order.

     (e) No Order. No Governmental Entity (including a federal or state court)
of competent jurisdiction shall have enacted, issued, promulgated, enforced or
entered any statute, rule, regulation, executive order, decree, injunction or
other order (whether temporary, preliminary or permanent) which is in effect


                                      A-22
<PAGE>

and which materially restricts, prevents or prohibits consummation of the Merger
or any transaction contemplated by this Agreement or has the effect of making
the Merger illegal; provided, however, that the parties shall use their
reasonable best efforts to cause any such decree, judgment, injunction or other
order to be vacated or lifted.


     (f) Approvals. Other than the filing of Merger documents in accordance with
the GCL, all authorizations, consents, waivers, orders or approvals of, or
declarations or filings with, or expirations of waiting periods imposed by, any
Governmental Entity the failure of which to obtain, make or occur would,
individually or in the aggregate, have a material adverse effect at or after the
Effective Time on Parent and its Subsidiaries including the Surviving
Corporation and its Subsidiaries, shall have been obtained, been filed or have
occurred. Parent shall have received all state securities or "blue sky" permits
and other authorizations necessary to issue the shares of Parent Common Stock
pursuant to this Agreement in the Merger.


     (g) Litigation. No preliminary or permanent injunction or other order shall
have been issued by any court or by any governmental or regulatory agency, body
or authority which enjoins, restrains or prohibits the transactions contemplated
hereby, including the consummation of the Merger or has the effect of making the
Merger illegal and which is in effect at the Effective Time (each party agreeing
to use its best efforts to have any such injunction or order lifted).


     Section 8.2 Conditions to Obligations of Parent and Sub to Effect the
Merger. The obligations of Parent and Sub to effect the Merger shall be subject
to the satisfaction at or prior to the Effective Time of the following
additional conditions, unless waived in writing by Parent:


     (a) Representations and Warranties. (i) The aggregate effect of all
inaccuracies in the representations and warranties of the Company set forth in
this Agreement does not and will not have a Company Material Adverse Effect and
(ii) the representations and warranties of the Company that are qualified with
reference to a Company Material Adverse Effect or materiality shall, subject to
such qualification, be true and correct and the representations and warranties
that are not so qualified shall be true and correct in all material respects, in
each case as of the date hereof, and, except to the extent such representations
and warranties speak as of an earlier date, as of the Effective Time as though
made at and as of the Effective Time, and Parent shall have received a
certificate signed on behalf of the Company by the chief executive officer or
the chief financial officer of the Company to such effect.


     (b) Performance of Obligations of the Company. The Company shall have
performed in all material respects all obligations required to be performed by
it under this Agreement at or prior to the Effective Time, and Parent shall have
received a certificate signed on behalf of the Company by the chief executive
officer or the chief financial officer of the Company to such effect.



     (c) Affiliate Agreements. Parent shall have received the Affiliate
Agreements from each of the Affiliates of the Company, as contemplated in
Section 7.6.


     (d) "Pooling Letter." Parent shall have received from KPMG LLP a letter,
dated the Closing Date and addressed to Parent, to the effect that, subject to
customary qualifications, KPMG LLP concurs with management's conclusion that the
Merger qualifies for pooling of interests treatment for financial reporting
purposes in accordance with GAAP, and Parent shall have received from the
Company, with the consent of Ernst & Young LLP, a copy of a letter, dated the
Closing Date, of Ernst & Young LLP addressed to the Company to the effect that,
subject to customary qualifications, the Merger qualifies for pooling of
interests for financial reporting purposes in accordance with GAAP.


     (e) Dissenting Shares. The aggregate number of shares of Company Common
Stock into which all Dissenting Shares are convertible shall not constitute more
than 5% of the number of shares of Company Common Stock outstanding as of
immediately prior to the Effective Time (calculated assuming no dilution).


     (f) Legal Opinion. Parent shall have received the opinion, dated the
Closing Date, of Cooley Godward LLP substantially to the effect set forth in
Exhibit D hereto.


                                      A-23
<PAGE>

     (g) Tax Opinion. Parent shall have received the legal opinion of Proskauer
Rose LLP dated as of the Closing Date and addressed to Parent, substantially to
the effect that the Merger will be treated for United States federal income tax
purposes as a reorganization within the meaning of Section 368 (a) of the Code
set forth in Exhibit E hereto (it being understood that, (i) in rendering such
opinion, Proskauer Rose LLP may rely upon the tax representation letters
referred to in Section 7.4, and (ii) if Proskauer Rose LLP does not render such
opinion or withdraws or modifies such opinion, this condition shall nonetheless
be deemed to be satisfied if Cooley Godward LLP renders such opinion, which
opinion shall not contain paragraph (g) on page 2 thereof).

     (h) Employment Agreements. The Company shall have entered into employment
agreements with such of its key employees as are deemed sufficient by Parent in
the exercise of its reasonable judgment and on terms reasonably acceptable to
Parent (it being understood that the Company will not be required to enter into
any employment agreement with any employee that voluntarily elects to leave
employment with the Company); and

     (i) Agreement with Nippon Kayaku Co., Ltd. The Company shall have
terminated or modified any and all agreements with Nippon Kayaku Co., Ltd. on
terms acceptable to Parent.

     Section 8.3 Conditions to Obligation of the Company to Effect the Merger.
The obligation of the Company to effect the Merger shall be subject to the
satisfaction at or prior to the Effective Time of the following additional
conditions:

     (a) Representations and Warranties. (i) The aggregate effect of all
inaccuracies in the representations and warranties of Parent set forth in this
Agreement does not and will not have a Parent Material Adverse Effect and (ii)
the representations and warranties of Parent contained in this Agreement that
are qualified with reference to a Parent Material Adverse Effect or materiality
shall be true and correct and the representations and warranties that are not so
qualified shall be true and correct in all material respects as of the date
hereof, and, except to the extent such representations and warranties speak as
of an earlier date, as of the Effective Time as though made on and as of the
Effective Time, and the Company shall have received a certificate signed on
behalf of Parent by the chief executive officer or the chief financial officer
of Parent to such effect.

     (b) Performance of Obligations of Parent and Sub. Each of Parent and Sub
shall have performed in all material respects all obligations required to be
performed by it under this Agreement at or prior to the Effective Time, and the
Company shall have received a certificate signed on behalf of Parent by the
chief executive officer or the chief financial officer of Parent to such effect.

     (c) Legal Opinion. The Company shall have received an opinion, dated the
Closing Date, of Proskauer Rose LLP, reasonably satisfactory to the Company,
substantially to the effect set forth in Exhibit F hereto.

     (d) Tax Opinion. The Company shall have received the legal opinion of
Cooley Godward LLP dated as of the Closing Date and addressed to the Company,
substantially to the effect that the Merger will be treated for United States
federal income tax purposes as a reorganization within the meaning of Section
368(a) of the Code set forth in Exhibit G hereto (it being understood that, (i)
in rendering such opinion, Cooley Godward LLP may rely upon the tax
representation letters referred to in Section 7.4, and (ii) if Cooley Godward
LLP does not render such opinion or withdraws or modified such opinion, this
condition shall nonetheless be deemed to be satisfied if Proskauer Rose LLP
renders such opinion, which opinion shall not contain paragraph (g) on page 2
thereof).


                                      A-24
<PAGE>

                                   ARTICLE IX

                                   TERMINATION


     Section 9.1 Termination. This Agreement may be terminated at any time prior
to the Effective Time, whether before or after approval by the shareholders of
the Company:


     (a) by mutual consent of Parent and the Company;


     (b) by either Parent or the Company, if (i) the Merger shall not have been
consummated before December 31, 2000, or (ii) the approval of the shareholders
of the Company required by Section 4.19 shall not have been obtained at a
meeting duly convened therefor or any adjournment thereof (unless, in the case
of any such termination pursuant to this Section 9.1(b), the failure to so
consummate the Merger by such date or to obtain such shareholder approval shall
have been caused by the action or failure to act of the party (or its
Subsidiaries) seeking to terminate this Agreement, which action or failure to
act constitutes a breach of this Agreement);


     (c) by either Parent or the Company, if any permanent injunction or action
by any Governmental Entity of competent jurisdiction preventing the consummation
of the Merger shall have become final and nonappealable; provided, however, that
the party seeking to terminate this Agreement pursuant to this Section 9.1(c)
shall have used all reasonable efforts to remove such injunction or overturn
such action;


     (d) by Parent, if (i) there has been a breach of any representations or
warranties (as of the time such representations or warranties were made) of the
Company set forth herein the effect of which, individually or together with all
other such breaches, is a Company Material Adverse Effect, (ii) there has been a
breach in any material respect of any of the covenants or agreements set forth
in this Agreement on the part of the Company, which breach is not curable or, if
curable, is not cured within 30 days after written notice of such breach is
given by Parent to the Company, or (iii) the Board of Directors of the Company
(x) withdraws or amends or modifies in a manner materially adverse to Parent or
Sub its recommendation or approval in respect of this Agreement or the Merger,
(y) makes any recommendation with respect to an Acquisition Transaction
(including making no recommendation or stating an inability to make a
recommendation), other than a recommendation to reject such Acquisition
Transaction, or (z) takes any action that would be prohibited by Section 7.2;
and


     (e) by the Company, if (i) there has been a breach of any representations
or warranties (as of the time such representations or warranties were made) of
Parent set forth herein the effect of which, individually or together with all
other such breaches, is a Parent Material Adverse Effect, or (ii) there has been
a breach in any material respect of any of the covenants or agreements set forth
in this Agreement on the part of Parent, which breach is not curable or, if
curable, is not cured within 30 days after written notice of such breach is
given by the Company to Parent.


     Section 9.2 Effect of Termination.


     (a) In the event of termination of this Agreement pursuant to this Article
IX, the Merger shall be deemed abandoned and this Agreement shall forthwith
become void, without liability on the part of any party hereto, except as
provided in this Section 9.2, Section 7.1 and Section 7.11.


     (b) If (x) Parent shall have terminated this Agreement pursuant to Sections
9.1(d)(iii) or (y) either (1) Parent shall have terminated this Agreement
pursuant to Section 9.1(b)(i) or Parent or the Company shall have terminated
this Agreement pursuant to Section 9.1(b)(ii) or (2) Parent shall have
terminated this Agreement pursuant to Section 9.1(d)(i) or 9.1(d)(ii) and, prior
to or within one (1) year after any termination described in this clause (y),
the Company (or any of its Subsidiaries) shall have directly or indirectly
entered into a definitive agreement for, or shall have consummated, an
Acquisition Transaction, then, in any of such cases, the Company shall pay
Parent a termination fee of ten million dollars ($10,000,000); provided,
however, that any liquidated damage amounts previously paid by the Company to
Parent pursuant to Section 9.2(c) shall be credited against the termination fee
payable under this Section 9.2(b). Any fees or amounts payable under this
Section 9.2(b) shall be paid in same day funds

                                      A-25
<PAGE>

no later than: (i) two business days after a termination described in clause (x)
of this Section 9.2(b); or (ii) concurrently with or prior to the entering into
of the definitive agreement for, or the consummation of, such Acquisition
Transaction, in the case of a termination described in clause (y) of this
Section 9.2(b).

     (c) If Parent shall have terminated this Agreement pursuant to Sections
9.1(d)(i) or 9.1(d)(ii), then, in any of such cases, the Company shall pay to
Parent as liquidated damages and not as a penalty, five million dollars
($5,000,000). Such liquidated damage amount shall be payable no later than two
business days after such termination.

     (d) If Company shall have terminated this Agreement pursuant to Sections
9.1(e)(i) or 9.1(e)(ii), then, in any of such cases, the Parent shall pay to
Company as liquidated damages and not as a penalty, five million dollars
($5,000,000). Such liquidated damage amount shall be payable no later than two
business days after such termination.


                                    ARTICLE X

                               GENERAL PROVISIONS

     Section 10.1 Amendment and Modification. At any time prior to the Effective
Time, this Agreement may be amended, modified or supplemented only by written
agreement (referring specifically to this Agreement) of Parent, Sub and the
Company with respect to any of the terms contained herein; provided, however,
that after any approval and adoption of this Agreement by the shareholders of
the Company, no such amendment, modification or supplementation shall be made
which under applicable law requires the approval of such shareholders, without
the further approval of such shareholders.

     Section 10.2 Waiver. At any time prior to the Effective Time, Parent and
Sub, on the one hand, and the Company, on the other hand, may (i) extend the
time for the performance of any of the obligations or other acts of the other,
(ii) waive any inaccuracies in the representations and warranties of the other
contained herein or in any documents delivered pursuant hereto and (iii) waive
compliance by the other with any of the agreements or conditions contained
herein which may legally be waived. Any such extension or waiver shall be valid
only if set forth in an instrument in writing specifically referring to this
Agreement and signed on behalf of such party.

     Section 10.3 Survivability; Investigations. The respective representations
and warranties of Parent and the Company contained herein or in any certificates
or other documents delivered prior to or as of the Effective Time (i) shall not
be deemed waived or otherwise affected by any investigation made by any party
hereto and (ii) shall not survive beyond the Effective Time. The covenants and
agreements of the parties hereto (including the Surviving Corporation after the
Merger) shall survive the Effective Time without limitation (except for those
which, by their terms, contemplate a shorter survival period).

     Section 10.4 Notices. All notices and other communications hereunder shall
be in writing and shall be delivered personally or by next-day courier or
telecopied with confirmation of receipt, to the parties at the addresses
specified below (or at such other address for a party as shall be specified by
like notice; provided that notices of a change of address shall be effective
only upon receipt thereof. Any such notice shall be effective upon receipt, if
personally delivered or telecopied, or one day after delivery to a courier for
next-day delivery.

   (a) If to Parent or Sub, to:

       Celgene Corporation
       7 Powder Horn Drive
       Warren, NJ 07059
       Fax: (732) 805-3931

       Attention:
                  ----------------

       with a copy to:

       Proskauer Rose LLP
       1585 Broadway


                                      A-26
<PAGE>

       New York, New York 10036
       Fax: (212) 969-2900

       Attention: Robert A. Cantone, Esq.


   (b) if to the Company, to:

       Signal Pharmaceuticals, Inc.
       5555 Oberlin Drive
       San Diego, CA 92121
       Fax:
            ----------------

       Attention:
                  ----------------


       with a copy to: Cooley Godward LLP
       4365 Executive Drive, Suite 1100
       San Diego, CA 92121
       Fax: (858) 453-3555

       Attention: L. Kay Chandler, Esq.


     Section 10.5 Descriptive Headings; Interpretation. The headings contained
in this Agreement are for reference purposes only and shall not affect in any
way the meaning or interpretation of this Agreement. References in this
Agreement to Sections, Schedules, Exhibits or Articles mean a Section, Schedule,
Exhibit or Article of this Agreement unless otherwise indicated. The term
"person" shall mean and include an individual, a partnership, a joint venture, a
limited liability company, a corporation, a trust, a Governmental Entity or an
unincorporated organization.

     Section 10.6 Entire Agreement; Assignment. This Agreement (including the
Schedules and other documents and instruments referred to herein), together with
the Proxy and Option Agreement and the Confidentiality Agreement, constitute the
entire agreement, and supersede all other prior agreements and understandings,
both written and oral, among the parties or any of them, with respect to the
subject matter hereof. This Agreement is not intended to confer upon any person
not a party hereto any rights or remedies hereunder, except as provided in
Section 7.15. This Agreement shall not be assigned by operation of law or
otherwise; provided that Parent or Sub may assign its rights and obligations
hereunder to a direct or indirect subsidiary of Parent, but no such assignment
shall relieve Parent or Sub, as the case may be, of its obligations hereunder.

     Section 10.7 Governing Law. This Agreement shall be governed by and
construed in accordance with the laws of the State of California without giving
effect to the provisions thereof relating to conflicts of law, except to the
extent relating to matters governed by the General Corporation Law of the State
of California.

     Section 10.8 Severability. In case any one or more of the provisions
contained in this Agreement should be invalid, illegal or unenforceable in any
respect against a party hereto, the validity, legality and enforceability of the
remaining provisions contained herein shall not in any way be affected or
impaired thereby and such invalidity, illegality or unenforceability shall only
apply as to such party in the specific jurisdiction where such judgment shall be
made.

     Section 10.9 Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original but all of which
shall constitute one and the same agreement.


                                      A-27
<PAGE>

     IN WITNESS WHEREFORE, each of Parent, Sub and the Company has caused this
Agreement to be executed on its behalf by its officers thereunto duly
authorized, all as of the date first above written.

                                        CELGENE CORPORATION




                                        By: /s/ John W. Jackson
                                           ------------------------------------

                                           Name: John W. Jackson
                                           Title: Chairman & CEO



                                        SIGNAL PHARMACEUTICALS, INC.




                                        By: /s/ Alan J. Lewis
                                           ------------------------------------

                                           Name: Alan J. Lewis
                                           Title: President and CEO



                                        CELGENE ACQUISITION CORP.




                                        By: /s/ Sol J. Barer
                                           ------------------------------------

                                           Name: Sol J. Barer, Ph.D.
                                           Title: President


                                      A-28
<PAGE>

                                    EXHIBIT A-1 TO AGREEMENT AND PLAN OF MERGER


                           VOTING AND PROXY AGREEMENT

     VOTING AND PROXY AGREEMENT dated as of __________, 2000, by and among
Celgene Corporation, a Delaware corporation ("Parent"), and the persons listed
on Schedule A hereto (collectively, the "Stockholders" and each a
"Stockholder"), each a stockholder of Signal Pharmaceuticals, Inc., a California
corporation (the "Company").

     Contemporaneously with the execution of this Agreement, the Company, Parent
and Cape May Acquisition Corp., a Delaware corporation and wholly-owned
subsidiary of Parent ("Sub"), are entering into an Agreement and Plan of Merger
(the "Merger Agreement") pursuant to which it is contemplated that Sub will be
merged with and into the Company (the "Merger") and the holders of the Company's
common stock (the "Company Common Stock") will be entitled to receive shares of
Parent's Common Stock, par value $.01 per share ("Parent Common Stock"), for
such shares of Company Common Stock.

     Parent, as a condition to its willingness to enter into the Merger
Agreement, has required the Stockholders to grant Parent an irrevocable proxy
with respect to all of the shares of Company Common Stock and the Company's
Preferred Stock, par value $____ per shares (the "Company Preferred Stock")
owned by the Stockholders, together with any additional shares of Company Common
Stock hereafter acquired by the Stockholders (pursuant to Section 7, by exercise
of options or warrants, by conversion of debentures or otherwise, acquired by
such Stockholder) (such specified number of shares, and any additional shares
when and if acquired, being referred to as the "Shares") on the terms and
conditions hereinafter set forth.

     The parties hereto agree as follows:

     1. Irrevocable Proxy. Each Stockholder hereby irrevocably constitutes and
appoints Parent or any designee of Parent the lawful agent, attorney and proxy
of such Stockholder during the term of this Agreement, to vote all of such
Stockholder's Shares that such Stockholder has an irrevocable proxy to vote at
any meeting or in connection with any written consent of the Company's
stockholders (a) in favor of the Merger, (b) in favor of the Merger Agreement,
as such may be modified or amended from time to time, (c) in favor of the
conversion of the Company Preferred Stock to Company Common Stock, such
conversion to be (i) on the terms provided for in the Certificate of
Incorporation of the Company, (ii) effective immediately prior to the date and
time the Merger becomes effective and (iii) subject to the Merger becoming
effective, (d) against any Acquisition Transaction (other than the Merger) or
other merger, sale, or other business combination between the Company and any
other person or entity or any other action which would make it impractical for
Parent to effect a merger or other business combination of the Company with
Parent or Sub, and (e) against any other action or agreement that would result
in a breach of any covenant, representation or warranty or any other obligation
or agreement of the Company under the Merger Agreement or which would result in
any of the Company's obligations under the Merger Agreement not being fulfilled.
This power of attorney is irrevocable, is granted in consideration of Parent
entering into the Merger Agreement and is coupled with an interest sufficient in
law to support an irrevocable power. This appointment shall revoke all prior
attorneys and proxies appointed by any Stockholder at any time with respect to
the Shares and the matters set forth in clauses (a) through (d) above and no
subsequent attorneys or proxies will be appointed by such Stockholder, or be
effective, with respect thereto.

     2. Representations and Warranties of the Stockholders. Each Stockholder
represents and warrants to Parent as follows:

     (a) Ownership of Shares. That Stockholder is the sole beneficial owner of
the number of Shares set forth as being granted to that Stockholder on Schedule
A. The Shares set forth opposite that Stockholder's name on Schedule A
constitute all the RightsShares owned beneficially or of record by that
Stockholder. The Shares owned by that Stockholder are validly issued, fully paid
and

<PAGE>

nonassessable and such Shares set forth opposite that Stockholder's name on
Schedule A, are held by that Stockholder, or by a nominee or custodian for the
benefit of that Stockholder, free and clear of all liens, claims, security
interests, agreements and other encumbrances, except for encumbrances arising
under this Agreement.

     (b) Power; Binding Agreement. That Stockholder has the legal capacity to
enter into and perform all of that Stockholder's obligations under this
Agreement. The execution, delivery and performance of this Agreement by that
Stockholder will not violate any other agreement to which that Stockholder is a
party, including, without limitation, any voting agreement, stockholders
agreement or voting trust. This Agreement has been duly and validly executed and
delivered by that Stockholder and constitutes a valid and binding obligation of
that Stockholder, enforceable against that Stockholder in accordance with its
terms, except as enforceability may be limited by applicable bankruptcy,
insolvency and similar laws affecting creditors' rights generally and subject to
general principles of equity. If that Stockholder is married and that
Stockholder's Shares constitute community property, this Agreement has been duly
authorized, executed and delivered by, and constitutes a valid and binding
obligation of, that Stockholder's spouse, enforceable against that spouse in
accordance with its terms, except as enforceability may be limited by applicable
bankruptcy, insolvency and similar laws affecting creditors' rights generally
and subject to general principles of equity.


     (c) Consents and Approvals; No Violation. Neither the execution and
delivery of this Agreement by that Stockholder nor the consummation of the
transactions contemplated by this Agreement will: (i) require any consent,
approval, authorization or permit of, or filing with or notification to, any
person or entity or any governmental or regulatory authority, except in
connection with the HSR Act or pursuant to the Securities Exchange Act of 1934;
(ii) conflict with, result in a breach of, or result in a default (or give rise
to a right of termination, cancellation or acceleration) under any of the terms,
conditions or provisions of any note, license, agreement or other instrument or
obligation to which that Stockholder is a party or by which that Stockholder or
any of that Stockholder's assets may be bound; or (iii) violate any order, writ,
injunction, decree, statute, rule or regulation applicable to that Stockholder
or by which any of that Stockholder's assets are bound.


     3. Representations and Warranties of Parent. Parent represents and warrants
to each Stockholder that:


     (a) Power; Binding Agreement. Parent has the corporate power and authority
to enter into and perform all its obligations under this Agreement. The
execution, delivery and performance of this Agreement by Parent will not violate
any other agreement to which Parent is a party. This Agreement has been duly and
validly authorized, executed and delivered by Parent and constitutes a valid and
binding obligation of Parent, enforceable against Parent in accordance with its
terms, except as enforceability may be limited by applicable bankruptcy,
insolvency and similar laws affecting creditors' rights generally and subject to
general principles of equity.


     (b) Consents and Approvals; No Violation. Neither the execution and
delivery of this Agreement by Parent nor the consummation by Parent of the
transactions contemplated by this Agreement will: (i) require any consent,
approval, authorization or permit of, or filing with or notification to, any
person or entity or any governmental or regulatory authority, except in
connection with the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as
amended or pursuant to the Securities Exchange Act of 1934; (ii) conflict with,
result in a breach of, or result in a default (or give rise to a right of
termination, cancellation or acceleration) under any of the terms, conditions or
provisions of any note, license, agreement or other instrument or obligation to
which Parent is a party or by which Parent or any of its assets may be bound; or
(iii) violate any order, writ, injunction, decree, statute, rule or regulation
applicable to Parent or by which any of its assets are bound.


     4. Additional Covenants of the Stockholders. Each Stockholder hereby
covenants and agrees that:


     (a) that Stockholder will not enter into any transaction, take any action,
or by inaction permit any event to occur that would (i) result in any of the
representations or warranties of such


                                      A-1-2
<PAGE>

Stockholder herein contained not being true and correct at and as of the time
immediately after the occurrence of such transaction, action or event; or (ii)
have the effect of preventing or disabling that Stockholder from performing that
Stockholder's obligations under this Agreement;

     (b) that Stockholder will not grant any proxies or powers of attorney with
respect to any Shares, deposit any Shares into a voting trust or enter into a
voting agreement with respect to such Shares; provided, however, that the
Stockholders may grant proxies to third parties provided that such proxies are
expressly made subject to the terms of this Agreement;

     (c) until the termination of this Agreement, such Stockholder will at all
times use his, her or its best efforts in his, her or its capacity as a
stockholder of the Company to prevent the Company from taking any action in
violation of the Merger Agreement;

     (d) from and after the date hereof until the termination of this Agreement,
other than under the circumstances contemplated by Section 7 hereof, the Shares
will not be sold, transferred, pledged, hypothecated, transferred by gift, or
otherwise disposed of in any manner whatsoever without notifying Parent in
advance and obtaining and delivering to Parent any evidence that Parent may
reasonably request to evidence the transferee's agreement to be bound by this
Agreement; provided, however, that in the event of such Stockholder's death
during the term of this Agreement, the Shares may be transferred in accordance
with the Stockholder's last will and testament, or if none, in accordance with
the applicable laws of intestate succession, in either of which cases, the
Shares shall remain subject in all respects to the terms of this Agreement; and

     (e) the Stockholder will execute and deliver any additional documents
reasonably necessary or desirable, in the opinion of Parent's or the Company's
counsel, to evidence the irrevocable proxy granted in Section 1 with respect to
the Shares or otherwise implement and effect the provisions of this Agreement.

     5. No Solicitation. No Stockholder shall, in that Stockholder's capacity as
such, directly or indirectly, (a) solicit, initiate, facilitate or encourage
(including by way of furnishing or disclosing non-public information) any
inquiries or the making of any proposal with respect to any Acquisition
Transaction, (b) negotiate, explore or otherwise engage in discussion with any
person (other than Parent and its representatives) with respect to any
Acquisition Transaction, (c) agree to or endorse an Acquisition Transaction with
any person (other than Parent or Sub) or any agreement, arrangement or
understanding with respect to any such Acquisition Transaction or which would
require the Company to abandon, terminate or fail to consummate the Merger or
any other transaction contemplated by this Agreement, or (d) authorize or permit
any person or entity acting on behalf of that Stockholder to do any of the
foregoing. If any Stockholder receives any inquiry or proposal regarding any
Acquisition Transaction, that Stockholder shall promptly inform Parent of that
inquiry or proposal.

     6. Legending of Certificates; Nominee Shares. Each Stockholder agrees to
submit to Parent contemporaneously with or promptly following execution of this
Agreement (or promptly following receipt of any additional certificates
representing any additional Shares) all certificates representing the Shares so
that Parent may note thereon a legend referring to the proxy granted to it by
this Agreement. If any of the Shares beneficially owned by a Stockholder are
held of record by a brokerage firm in "street name" or in the name of any other
nominee (a "Nominee," and, as to such Shares, "Nominee Shares"), the Stockholder
agrees that, upon written notice by Parent requesting it, such Stockholder will
within five days of the giving of such notice execute and deliver to Parent a
limited power of attorney in such form as shall be reasonably satisfactory to
Parent enabling Parent to require the Nominee to grant to Parent an irrevocable
proxy to the same effect as Section 1 hereof with respect to the Nominee Shares
held by such Nominee and to submit to Parent the certificates representing such
Nominee Shares for notation of the above-referenced legend thereon.

     7. Adjustments to Prevent Dilution, Etc. In the event of a stock dividend
or distribution, or any change in Company Common Stock by reason of any stock
dividend, split-up, recapitalization, combination, exchange of shares or the
like, the term "Shares" shall be deemed to refer to and include the Shares as
well as all such stock dividends and distributions and any shares into which or
for which any or all of the Shares may be changed or exchanged.


                                      A-1-3
<PAGE>

     8. Stockholder Capacity. No person executing this Agreement who is or
becomes during the term of this Agreement a director of the Company makes any
agreement in his or her capacity as a director. Each Stockholder is executing
and delivering this Agreement solely in that Stockholder's capacity as the
record and beneficial owner of that Stockholder's Shares. Notwithstanding
anything to the contrary in this Agreement, no action or inaction by a
Stockholder in his capacity as a director, officer, or employee of the Company
shall be deemed to contravene Section 5, as long as the action or inaction does
not contravene Section 7.2 of the Merger Agreement.

     9. Termination. This Agreement shall terminate on the Effective Time of the
Merger; provided, however, that the appointment of Parent or any designee of
Parent as agent, attorney and proxy pursuant to Section 1 hereof, and any proxy
or other instrument executed pursuant thereto, shall in any event automatically
terminate upon the termination of the Merger Agreement.

     10. Miscellaneous.

     (a) No Waiver. The failure of any party to exercise any right, power or
remedy under this Agreement or otherwise available in respect of this Agreement
at law or in equity, or to insist upon compliance by any other party with that
party's obligations under this Agreement, shall not constitute a waiver of any
right to exercise any such or other right, power or remedy or to demand such
compliance.

     (b) Notices. All notices and other communications hereunder shall be in
writing and shall be delivered personally or by next-day courier or telecopied
with confirmation of receipt, to the parties at the addresses specified below
(or at such other address for a party as shall be specified by like notice;
provided that notices of a change of address shall be effective only upon
receipt thereof). Any such notice shall be effective upon receipt, if personally
delivered or telecopied, or one day after delivery to a courier for next-day
delivery.

   (i) If to Parent, to:

            Celgene Corporation

            -------------------------
            -------------------------
            Attn:

     with a copy to:

            Proskauer Rose LLP
            1585 Broadway
            New York, New York 10036
            Attention: Robert A. Cantone, Esq.

     (ii) if to a Stockholder, to:

            -------------------------
            -------------------------
            -------------------------
            -------------------------

     with a copy to:

            -------------------------
            -------------------------
            -------------------------
            Fax:
            Attention:


                                      A-1-4
<PAGE>

     (c) Descriptive Headings; Interpretation. The headings contained in this
Agreement are for reference purposes only and shall not affect in way the
meaning or interpretation of this Agreement. References in this Agreement to
Sections and Schedules mean a Section or Schedule of this Agreement unless
otherwise indicated. The terms "beneficially own" and "beneficial owner" with
respect to any securities shall have the same meaning as in, and shall be
determined in accordance with, Rule 13d-3 under the Securities Exchange Act of
1934.

     (d) Entire Agreement; Assignment. This Agreement (including the schedule
and other documents and instruments referred to herein), together with the
Merger Agreement, constitute the entire agreement and supersede all other prior
agreements and understandings, both written and oral, among the parties or any
of them, with respect to the subject matter hereof. Except as otherwise
expressly provided herein, this Agreement is not intended to confer upon any
person not a party hereto any rights or remedies hereunder. Except as otherwise
expressly provided herein, this Agreement shall not be assigned by operation of
law or otherwise; provided that Parent or Sub may assign its rights and
obligations hereunder to a direct or indirect subsidiary of Parent, but no such
assignment shall relieve Parent or Sub, as the case may be, of its obligations
hereunder.

     (e) Liability After Transfer. Each Stockholder agrees that, notwithstanding
any transfer of that Stockholder's Shares in accordance with Section 4(d), that
Stockholder shall remain liable for his or her performance of all obligations
under this Agreement.

     (f) Injunctive Relief; Remedies Cumulative.

     (i) Parent, on the one hand, and the Stockholders, on the other hand,
acknowledge that the other party will be irreparably harmed and that there will
be no adequate remedy at law for a violation of any of the covenants or
agreements of such party that are contained in this Agreement. It is accordingly
agreed that, in addition to any other remedies that may be available to the
non-breaching party upon the breach by any other party of such covenants and
agreements, the non-breaching party shall have the right to obtain injunctive
relief to restrain any breach or threatened breach of such covenants or
agreements or otherwise to obtain specific performance of any of such covenants
or agreements.

     (ii) No remedy conferred upon or reserved to any party herein is intended
to be exclusive of any other remedy and every remedy shall be cumulative and in
addition to every other remedy herein or now or hereafter existing at law, in
equity or by statute.

     (g) Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of California without giving effect to the
provisions thereof relating to conflicts of laws.

     (h) Effect of Partial Invalidity. Whenever possible, each provision of this
Agreement shall be construed in such a manner as to be effective and valid under
applicable law. If any provision of this Agreement or the application thereof to
any party or circumstance shall be prohibited by or invalid under applicable
law, such provisions shall be ineffective to the extent of such prohibition
without invalidating the remainder of such provision or any other provisions of
this Agreement or the application of such provision to the other party or other
circumstances.

     (i) Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original but all of which
shall constitute one and the same agreement.


                                      A-1-5
<PAGE>

     IN WITNESS WHEREOF, this Agreement has been executed by the parties as of
the date first above written.

                                          THE STOCKHOLDERS:



                                          -------------------------------------

                                          -------------------------------------

                                          -------------------------------------

                                          -------------------------------------

                                          CELGENE CORPORATION





                                        By: ----------------------------------
                                                  Authorized Officer

                                      A-1-6
<PAGE>

                                                                     EXHIBIT A-2


                                OPTION AGREEMENT

     OPTION AGREEMENT dated as of __________, 2000, by and among Celgene
Corporation, a Delaware corporation ("Parent") and Signal Pharmaceuticals, Inc.,
a California corporation (the "Company").

     Contemporaneously with the execution of this Agreement, the Company, Parent
and Celgene Acquisition Corp., a California corporation and wholly-owned
subsidiary of Parent ("Sub"), are entering into an Agreement and Plan of Merger
(the "Merger Agreement") pursuant to which it is contemplated that Sub will be
merged with and into the Company (the "Merger") and the holders of the Company's
Common Stock, (the "Company Common Stock") including holders of the Company's
Preferred Stock (the "Company Preferred Stock") which is to be converted
immediately prior to the Merger, will be entitled to receive shares of Parent's
Common Stock, par value $.01 per share ("Parent Common Stock"), for such shares
of Company Common Stock.

     Parent, as a condition to its willingness to enter into the Merger
Agreement, has required the Company to grant Parent an option with respect to
2,000,000 shares of Company Common Stock (the "Shares") and stock appreciation
rights with respect to 3,000,000 shares of the Company Common Stock on the terms
and conditions hereinafter set forth.

     The parties hereto agree as follows:

     1. Grant of Option and Stock Appreciation Right.

        (a) The Company hereby grants to Parent an option (collectively, the
"Option") to purchase the Shares and stock appreciation rights with respect to
3,000,000 shares of the Company Common Stock on the terms and conditions
hereinafter set forth. The consideration for the purchase of such Shares shall
be cash in the amount of $6.60 per share of Common Stock (the "Exercise Price").

     2. Exercise of Option. The Option shall be exercisable, in whole, but not
in part, by Parent as follows:

        (a) If the Merger Agreement is terminated by Parent pursuant to Section
9.1(d)(iii) of the Merger Agreement, then Parent may exercise the Option at any
time during the one year period beginning on the date of such termination.

        (b) If (i) the Merger Agreement is terminated by Parent pursuant to
Sections 9.1(d)(i) or 9.1(d)(ii) of the Merger Agreement, by Parent pursuant to
Section 9.1(b)(i), or by either Parent or the Company pursuant to Section
9.1(b)(ii), and (ii) the Company (or any of its Subsidiaries) shall have,
directly or indirectly, entered into a definitive agreement for, or shall have
consummated, an Acquisition Transaction, as that term is defined in the Merger
Agreement, within one year of such termination, then Parent may exercise the
Option during the period beginning on the date on which Parent first receives
notice of the occurrence of the event triggering Parent's right to exercise the
Option and ending on the date three business days after the date that the
Acquisition Transaction (or any successive Acquisition Transaction or any other
Acquisition Transaction made in response thereto) occurs.

     At any time when Parent wishes to exercise the Option, Parent shall give
written notice (the "Notice") to the Company specifying a place and a date not
less than two nor more than 20 business days from the date of the Notice for the
closing of such purchase (the "Closing"); provided, however, that such date may
be extended to the extent necessary to comply with the Hart-Scott-Rodino
Antitrust Improvements Act of 1976, as amended (the "HSR Act"), and applicable
regulations thereunder. The date on which the Parent gives the Notice shall be
deemed to be the date on which the Option is exercised. The Company agrees to
use its reasonable best efforts (subject to any applicable fiduciary duties) to
give Parent at least five business days prior written notice of the occurrence
of any event triggering Parent's right to exercise the Option.


                                      A-2-1
<PAGE>

     3. Payment and delivery of Certificate(s). At the Closing hereunder:

        (a) Parent will pay to the Company the aggregate Exercise Price for the
Shares and the Company will deliver to Parent against receipt of such aggregate
Exercise Price as provided in Section 3(a), a certificate or certificates
representing the Shares so purchased by Parent.

        (b) Notwithstanding any provisions herein to the contrary, in lieu of
exercising this Option for cash, Parent may elect to receive Shares equal to the
value (as determined below) of this Option by surrender of this Option in which
event the Company shall issue to Parent the number of Shares computed using the
following formula:

                                  X = Y(A-B)
                                     ------
                                        A
Where    X = the number of Shares to be issued to Parent;

         Y = the total number of Shares purchasable under this Option
             (at the date of such calculation);

         A = the greater of $6.60 or the consideration per share of Signal
             Pharmaceuticals Common Stock in the "Acquisition Transaction", if
             any, triggering Parent's right to exercise the Option; and

         B = Exercise Price (as adjusted to the date of such calculation).

For purposes of Rule 144 under the Securities Act, 17 CFR (section)230.144,
Parent and the Company agree that the exercise of this Option in accordance with
this Section 3(b) shall be deemed to be a conversion of such portion of the
Option, pursuant to the terms hereof, into Shares, to the fullest extent
permitted under such rule.

     3A. Stock Appreciation Rights. In the event that Parent exercises the
Option and thereafter sells or otherwise disposes of the Shares, the Company
shall forthwith pay to Parent an amount in cash equal to (a) 3,000,000
multiplied by (b) the excess, if any, of the amount per Share realized by Parent
in such sale or other disposition over the Exercise Price. For purposes of this
Section 3A, the value of any non-cash consideration received for the Shares
shall equal the fair market value on the date of such sale or other disposition.

     4. Additional Covenants of the Company. The Company hereby covenants and
agrees that:

        (a) the Company will not enter into any transaction, take any action, or
by inaction permit any event to occur that would have the effect of preventing
or disabling the Company from performing its obligations under this Agreement;
and

        (b) the Company will execute and deliver any additional documents
reasonably necessary or desirable, in the opinion of Parent's or the Company's
counsel, to evidence the option granted in Section 1 with respect to the Shares
or otherwise implement and effect the provisions of this Agreement.

     5. Reservation of Shares. The Company shall at all times reserve and keep
available out of authorized and unissued Company Common Stock, solely for the
purpose of providing for the exercise of the rights to purchase all Shares
granted pursuant to this Option, such number of shares of Company Common Stock
as shall, from time to time, be sufficient therefor. The Company covenants that
all shares of Company Common Stock issuable upon exercise of this Option, upon
receipt by the Company of the Exercise Price therefor or cancellation of this
Option pursuant to Section 3(b) hereof, shall be validly issued, fully paid,
nonassessable, and free of preemptive rights.

     6. Adjustments. (a) In case the Company shall at any time after the date
hereof (i) declare a dividend on the outstanding Company Common Stock payable in
shares of its capital stock, (ii) subdivide the outstanding Company Common
Stock, (iii) combine the outstanding Company Common Stock into a smaller number
of shares, or (iv) issue any shares of its capital stock by reclassification of
the Company Common Stock (including any such reclassification in connection with
a


                                      A-2-2
<PAGE>

consolidation or merger in which the Company is the continuing corporation),
then, in each case, the Exercise Price, and the number and kind of shares of
Company Common Stock receivable upon exercise of this Option, in effect at the
time of the record date for such dividend or of the effective date of such
subdivision, combination, or reclassification, shall be proportionately adjusted
so that Parent after such time shall be entitled to receive the aggregate number
and kind of shares which, if this Option had been exercised immediately prior to
such time, Parent would have owned upon such exercise and been entitled to
receive by virtue of such dividend, subdivision, combination, or
reclassification. Such adjustment shall be made successively whenever any event
listed above shall occur.


        (b) In case the Company shall issue or fix a record date for the
issuance to all holders of Company Common Stock of rights, options, or warrants
to subscribe for or purchase Company Common Stock (or securities convertible
into or exchangeable for Company Common Stock) at a price per share (or having a
conversion or exchange price per share, if a security convertible into or
exchangeable for Company Common Stock) less than the Current Market Price per
share of Company Common Stock (as defined in Section 6(e) hereof) on such record
date, then, in each case, the Exercise Price shall be adjusted by multiplying
the Exercise Price in effect immediately prior to such record date by a
fraction, the numerator of which shall be the number of shares of Company Common
Stock outstanding on such record date plus the number of shares of Company
Common Stock which the aggregate offering price of the total number of shares of
Company Common Stock so to be offered (or the aggregate initial conversion or
exchange price of the convertible or exchangeable securities so to be offered)
would purchase at such Current Market Price and the denominator of which shall
be the number of shares of Company Common Stock outstanding on such record date
plus the number of additional shares of Company Common Stock to be offered for
subscription or purchase (or into which the convertible or exchangeable
securities so to be offered are initially convertible or exchangeable). Such
adjustment shall become effective at the close of business on such record date;
provided, however, that, to the extent the shares of Company Common Stock (or
securities convertible into or exchangeable for shares of Company Common Stock)
are not delivered, the Exercise Price shall be readjusted after the expiration
of such rights, options, or warrants, to the Exercise Price which would then be
in effect had the adjustments made upon the issuance of such rights, options, or
warrants been made upon the basis of delivery of only the number of shares of
Company Common Stock (or securities convertible into or exchangeable for shares
of Company Common Stock) actually issued. In case any subscription price may be
paid in a consideration part or all of which shall be in a form other than cash,
the value of such consideration shall be as determined in good faith by the
board of directors of the Company, whose determination shall be conclusive
absent manifest error. Shares of Company Common Stock owned by or held for the
account of the Company or any majority-owned subsidiary shall be not deemed
outstanding for the purpose of any such computation.


        (c) In case the Company shall distribute to all holders of Company
Common Stock (including any such distribution made to the stockholders of the
Company in connection with a consolidation or merger in which the Company is the
continuing corporation) evidences of its indebtedness or assets (other than cash
dividends or distributions and dividends payable in shares of Company Common
Stock), or rights, options, or warrants to subscribe for or purchase Company
Common Stock, or securities convertible into or exchangeable for shares of
Company Common Stock (excluding any of the foregoing with respect to the
issuance of which an adjustment of the Exercise Price is provided pursuant to
Section 6(b) hereof), then, in each case, the Exercise Price shall be adjusted
by multiplying the Exercise Price in effect immediately prior to the record date
for the determination of stockholders entitled to receive such distribution by a
fraction, the numerator of which shall be the Current Market Price per share of
Company Common Stock on such record date, less the fair market value (as
determined in good faith by the board of directors of the Company, whose
determination shall be conclusive absent manifest error) of the portion of the
evidences of indebtedness or assets so to be distributed, or of such rights,
options, or warrants or convertible or exchangeable securities, applicable to
one share, and the denominator of which shall be such Current Market Price per
share of Company Common Stock. Such adjustment shall be made whenever any


                                      A-2-3
<PAGE>

such distribution is made, and shall become effective on the date of such
distribution retroactive to the record date for the determination of
shareholders entitled to receive such distribution.

     (d) For the purpose of any computation under this Section 6, the Current
Market Price per share of Company Common Stock on any date shall be deemed to be
the average of the daily closing prices for the 30 consecutive trading days
immediately preceding the date in question. The closing price for each day shall
be the last reported sales price regular way or, in case no such reported sale
takes place on such day, the closing bid price regular way, in either case on
the principal national securities exchange (including, for purposes hereof, the
NASDAQ National Market System) on which the Company Common Stock is listed or
admitted to trading or, if the Company Common Stock is not listed or admitted to
trading on any national securities exchange, the highest reported bid price for
the Company Common Stock as furnished by the National Association of Securities
Dealers, Inc. through NASDAQ or a similar organization if NASDAQ is no longer
reporting such information. If on any such date the Company Common Stock is not
listed or admitted to trading on any national securities exchange and is not
quoted by NASDAQ or any similar organization, the fair value of a share of
Company Common Stock on such date, as determined in good faith by the board of
directors of the Company, whose determination shall be conclusive absent
manifest error, shall be used.

        (e) No adjustment in the Exercise Price shall be required if such
adjustment is less than $.05; provided, however, that any adjustment which by
reason of this Section 6 are not required to be made shall be carried forward
and taken into account in any subsequent adjustment. All calculations under this
Section 6 shall be made to the nearest cent or to the nearest one-thousandth of
a share, as the case may be.

        (f) In any case in which this Section 6 shall require that an adjustment
in the Exercise Price be made effective as of a record date for a specified
event, the Company may elect to defer, until the occurrence of such event,
issuing to Parent, if Parent exercised this Option after such record date, the
shares of Company Common Stock, if any, issuable upon such exercise over and
above the shares of Company Common Stock, if any, issuable upon such exercise on
the basis of the Exercise Price in effect prior to such adjustment; provided,
however, that the Company shall deliver to Parent a due bill or other
appropriate instrument evidencing Holder's right to receive such additional
shares upon the occurrence of the event requiring such adjustment.

        (g) Upon each adjustment of the Exercise Price as a result of the
calculations made in Sections 6(b) or 6(c) hereof, this Option shall thereafter
evidence the right to purchase, at the adjusted Exercise Price, that number of
Shares (calculated to the nearest thousandth) obtained by dividing (i) the
product obtained by multiplying the number of shares purchasable upon exercise
of this Option prior to adjustment of the number of shares by the Exercise Price
in effect prior to adjustment of the Exercise Price by (ii) the Exercise Price
in effect after such adjustment of the Exercise Price.

        (h) Whenever there shall be an adjustment as provided in this Section 6,
the Company shall promptly cause written notice thereof to be sent by registered
mail, postage prepaid, to Parent, at its address set forth in the Merger
Agreement, which notice shall be accompanied by an officer's certificate setting
forth the number of Shares purchasable upon the exercise of this Option and the
Exercise Price after such adjustment and setting forth a brief statement of the
facts requiring such adjustment and the computation thereof, which officer's
certificate shall be conclusive evidence of the correctness of any such
adjustment absent manifest error.

        (i) The Company shall not be required to issue fractions of shares of
Company Common Stock of other capital stock of the Company upon the exercise of
this Option. If any fraction or a share would be issuable on the exercise of
this Option (or specified portions thereof), the Company shall purchase such
fraction for an amount in cash equal to the same fraction of the Current Market
Price of such share of Company Common Stock on the date of exercise of this
Option.


                                      A-2-4
<PAGE>

     7. Mergers; Reclassifications.

        (a) In case of any consolidation with or merger of the Company with or
into another corporation (other than a merger or consolidation in which the
Company is the surviving or continuing corporation), such successor corporation
shall (i) execute with Parent an agreement providing that Parent shall have the
right thereafter to receive upon exercise of this Option solely the kind and
amount of shares of stock and other securities, property, cash, or any
combination thereof receivable upon such consolidation, merger, sale, lease, or
conveyance by a holder of the number of shares of Company Common Stock for which
this Option might have been exercised immediately prior to such consolidation,
merger, sale, lease, or conveyance and (ii) make effective provision in its
certificate of incorporation or otherwise, if necessary, to effect such
agreement. Such agreement shall provide for adjustments which shall be as nearly
equivalent as practicable to the adjustments in Section 6.

        (b) In case of any reclassification or change of the shares of Company
Common Stock issuable upon exercise of this Option (other than as a result of a
subdivision or combination, but including any change in the shares into two or
more classes or series of shares), or in case of any consolidation or merger of
another corporation into the Company in which the Company is the continuing
corporation and in which there is a reclassification or change (including a
change to the right to receive cash or other property) of the shares of Company
Common Stock (other than as a result of a subdivision or combination, but
including any change in the shares into two or more classes or series of
shares), Parent shall have the right thereafter to receive upon exercise of this
Option solely the kind and amount of shares of stock and other securities,
property, cash, or any combination thereof receivable upon such
reclassification, change, consolidation, or merger by a holder of the number of
shares of Company Common Stock for which this Option might have been exercised
immediately prior to such reclassification, change, consolidation, or merger.
Thereafter, appropriate provision shall be made for adjustments which shall be
as nearly equivalent as practicable to the adjustments in Section 6.

       (c) The  above  provisions  of this  Section 7 shall  similarly  apply to
successive  reclassifications  and changes of shares of Company Common Stock and
to successive consolidations, mergers, sales, leases, or conveyances.

     8. Notice  of Certain Events. In case at any time the Company shall propose


        (a) to pay any dividend or make any distribution on shares of Company
Common Stock in shares of Company Common Stock or make any other distribution
(other than regularly scheduled cash dividends which are not in a greater amount
per share than the most recent such cash dividend) to all holders of Company
Common Stock; or

        (b) to issue any rights, warrants, or other securities to all holders of
Company Common Stock entitling them to purchase any additional shares of Company
Common Stock or any other rights, warrants, or other securities; or

        (c) to effect any reclassification or change of outstanding shares of
Company Common Stock, or any consolidation or merger described in Section 7; or


        (d) to effect any liquidation, dissolution, or winding-up of the
Company; or

        (e) to take any other action which would cause an adjustment to the
Exercise Price;

then, and in any one or more of such cases, the Company shall give written
notice thereof, by registered mail, postage prepaid, to Parent at Parent's
address as set forth in the Merger Agreement, mailed at least 15 days prior to
the earliest of (i) the date as of which the holders of record of shares of
Company Common Stock to be entitled to receive any such dividend, distribution,
rights, warrants, or other securities are to be determined, (ii) the date on
which any such reclassification, change of outstanding shares of Company Common
Stock, consolidation, merger, liquidation, dissolution, or winding-up is
expected to become effective, and the date as of which it is expected that
holders of record of shares of Company Common Stock shall be entitled to
exchange their shares for securities


                                      A-2-5
<PAGE>

or other property, if any, deliverable upon such reclassification, change of
outstanding shares, consolidation, merger, sale, lease, conveyance of property,
liquidation, dissolution, or winding-up, or (iii) the date of such action which
would require an adjustment to the Exercise Price.


     9. Registration.  Promptly after this Option shall become exercisable,  the
Company shall use its best efforts to obtain all requisite consents to the grant
to Parent of the registration rights set forth in this Section 9 and Section 10.
Unless and until such consents are obtained, this Section 9 and Section 10 shall
not become effective.


        (a) If, at any time during the Exercise Period or during the five-year
period following the exercise of this Option, the Company shall file a
registration statement (other than on Form S-4, Form S-8, or any successor
forms) with the Securities and Exchange Commission (the "Commission") covering,
in whole or in part, securities of the Company held by any person or entity
other than the Company, the Company shall give Parent at least 30 days prior
written notice of the filing of such registration statement. If requested by
Parent in writing within 20 days after receipt of any such notice, the Company
shall, at the Company's sole expense (other than the fees and disbursements of
counsel for Parent and the underwriting discounts, if any, payable in respect of
the Registrable Securities (as hereinafter defined) sold by Parent), use its
best efforts to register or qualify all or, at Parent's option, any portion of
the Registrable Securities concurrently with the registration of such other
securities, all to the extent requisite to permit the public offering and sale
of the Registrable Securities through the facilities of all appropriate
securities exchanges and the over-the-counter market, and will use its best
efforts through its officers, directors, auditors, and counsel to cause such
registration statement to become effective as promptly as practicable, subject
to any rights under that certain Amended and Restated Investor Rights Agreement,
dated September 9, 1997, as amended, between the Company and the investors named
therein. As used herein, "Registrable Securities" shall mean this Option and the
Shares which, in each case, have not been previously sold pursuant to a
registration statement or Rule 144 promulgated under the Securities Act and
which may not be sold by Parent pursuant to such Rule 144.


        (b) In the event of a registration pursuant to the provisions of this
Section 9, the Company shall use its best efforts to cause the Registrable
Securities so registered to be registered or qualified for sale under the
securities or blue sky laws of such jurisdictions as Parent may reasonably
request; provided, however, that the Company shall not be required to qualify to
do business in any state by reason of this Section 9(b) in which it is not
otherwise required to qualify to do business.


        (c) The Company shall keep effective any registration or qualification
contemplated by this Section 9 and shall from time to time amend or supplement
each applicable registration statement, preliminary prospectus, final
prospectus, application, document, and communication for such period of time as
shall be required to permit Parent to complete the offer and sale of the
Registrable Securities covered thereby on the terms described therein.


        (d) In the event of a registration pursuant to the provisions of this
Section 9, the Company shall furnish to Parent such number of copies of the
registration statement and of each amendment and supplement thereto (in each
case, including all exhibits), such reasonable number of copies of each
prospectus contained in such registration statement and each supplement or
amendment thereto (including each preliminary prospectus), all of which shall
conform to the requirements of the Securities Act and the rules and regulations
thereunder, and such other documents, as Parent may reasonably request to
facilitate the disposition of the Registrable Securities included in such
registration.


        (e) In the event of a registration pursuant to the provision of this
Section 9, Parent shall enter into a cross-indemnity agreement and a
contribution agreement, each in customary form, with each underwriter, if any,
and, if requested, enter into an underwriting agreement containing conventional
representations, warranties, allocation of expenses, and customary closing
conditions, including, but not limited to, opinions of counsel, with any
underwriter who acquires any Registrable Securities.


                                      A-2-6
<PAGE>

     10. Indemnification.


        (a) Subject to the conditions set forth below, the Company agrees to
indemnify and hold harmless Parent, its officers, directors, partners,
employees, agents, and counsel, and each person, if any, who controls any such
person within the meaning of Section 15 of the Securities Act or Section 20(a)
of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), from
and against any and all loss, liability, charge, claim, damage, and expense
whatsoever (which shall include, for all purposes of this Section 10, but not
limited to, reasonable attorneys' fees and any and all reasonable expense
whatsoever incurred in investigating, preparing, or defending against any
litigation, commenced or threatened, or any claim whatsoever, and any and all
amounts paid in settlement of any claim or litigation), as and when incurred,
arising out of, based upon, or in connection with any untrue statement or
alleged untrue statement of a material fact contained (A) in any registration
statement, preliminary prospectus, or final prospectus (as from time to time
amended and supplemented), or any amendment or supplement thereto, relating to
the sale of any of the Registrable Securities, or (B) in any application or
other document or communication (in this Section 10 collectively called an
"application") executed by or on behalf of the Company or based upon written
information furnished by or on behalf of the Company filed in any jurisdiction
in order to register or qualify any of the Registrable Securities under the
securities or blue sky laws thereof or filed with the Commission or any
securities exchange; or any omission or alleged omission to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading, unless such statement or omission was made in reliance upon and
in conformity with written information furnished to the Company with respect to
Parent by or on behalf of Parent expressly for inclusion in any registration
statement, preliminary prospectus, or final prospectus, or any amendment or
supplement thereto, or in any application, as the case may be. The foregoing
agreement to indemnify shall be in addition to any liability the Company may
otherwise have, including liabilities arising under this Option.


     If any action is brought against Parent or any of its officers, directors,
partners, employees, agents, or counsel, or any controlling persons of such
person (an "indemnified party") in respect of which indemnity may be sought
against the Company pursuant to the foregoing paragraph, such indemnified party
or parties shall promptly notify the Company in writing of the institution of
such action (but the failure so to notify shall not relieve the Company from any
liability pursuant to this Section 10(a) or otherwise, except to the extent it
may have been prejudiced in any material respect by such failure), and the
Company shall promptly assume the defense of such action, including the
employment of counsel reasonably satisfactory to such indemnified party or
parties and payment of expenses. Such indemnified party or parties shall have
the right to employ its or their own counsel in any such case, but the fees and
expenses of such counsel shall be at the expense of such indemnified party or
parties unless the employment of such counsel shall have been authorized in
writing by the Company in connection with the defense of such action or the
Company shall not have promptly employed counsel reasonably satisfactory to such
indemnified party or parties to have charge of the defense of such action or
such indemnified party or parties shall have reasonably concluded that there may
be one or more legal defenses available to it or them or to other indemnified
parties which are different from or additional to those available to the Company
and such indemnified party or parties shall have reasonably concluded that the
availability of such defenses necessitates such indemnified party or parties
employing its or their own counsel, in any of which events such fees and
expenses shall be borne by the Company and the Company shall not have the right
to direct the defense of such action on behalf of the indemnified party or
parties; provided, however, that the Company shall in no event be obligated to
pay for more than one such counsel. Anything in this Section 10 to the contrary
notwithstanding, the Company shall not be liable for any settlement of any such
claim or action effected without its written consent, which consent shall not be
unreasonably withheld. The Company shall not, without the prior written consent
of each indemnified party that is not released as described in this sentence,
settle or compromise any action, or permit a default or consent to the entry of
judgment in or otherwise seek to terminate any pending or threatened action, in
respect of which indemnity may be sought hereunder (whether or not any
indemnified party is a party thereto), unless such settlement, compromise,
consent or termination includes an unconditional release of each


                                      A-2-7
<PAGE>

indemnified party from all liability in respect of such action. The Company
agrees promptly to notify Parent of the commencement of any litigation or
proceedings against the Company or any of its officers or directors in
connection with the sale of any Registrable Securities or any preliminary
prospectus, prospectus, registration statement, or amendment or supplement
thereto, or any application relating to any sale of any Registrable Securities.


     With respect to any untrue statement or alleged untrue statement made in,
or omission or alleged omission from, any preliminary prospectus or final
prospectus, the indemnity agreement contained in this Section 10(a) with respect
to such preliminary prospectus or final prospectus, to the extent it is based on
the claim of a person who purchased Registrable Securities from Parent, shall
not inure to the benefit of Parent (or to the benefit of any of its officers,
directors, partners, employees, agents, counsel, or any person controlling
Parent) if the final prospectus (or the final prospectus as amended or
supplemented if the Company shall have filed with the Commission any amendment
or supplement thereto) which shall have been furnished to Parent prior to the
time written confirmation of such sale was sent to such person does not contain
such statement, alleged statement, omission, or alleged omission and a copy of
the final prospectus (or the final prospectus as amended or supplemented if the
Company shall have filed with the Commission any amendment or supplement
thereto) shall not have been sent or given to such person and such person shall
not otherwise have received a copy thereof at or prior to the written
confirmation of such sale to such person.

       (b) Parent agrees to indemnify and hold harmless the Company, each
director of the Company, each officer of the Company who shall have signed any
registration statement covering Registrable Securities held by Parent, each
other person, if any, who controls the Company within the meaning of Section 15
of the Securities Act or Section 20(a) of the Exchange Act, and its or their
respective counsel, to the same extent as the foregoing indemnity from the
Company to Parent in Section 10(a), but only with respect to statements or
omissions, if any, made in any registration statement, preliminary prospectus,
or final prospectus (as from time to time amended and supplemented), or any
amendment or supplement thereto, or in any application, in reliance upon and in
conformity with written information furnished to the Company with respect to
Parent by or on behalf of Parent expressly for inclusion in any such
registration statement, preliminary prospectus, or final prospectus, or any
amendment or supplement thereto, or in any application, as the case may be. If
any action shall be brought against the Company or any other person so
indemnified based on any such registration statement, preliminary prospectus, or
final prospectus, or any amendment or supplement thereto, or in any application,
and in respect of which indemnity may be sought against Parent pursuant to this
Section 10(b), Parent shall have the rights and duties given to the Company, and
the Company and each other person so indemnified shall have the rights and
duties given to the indemnified parties, by the provisions of Section 10(a).

       (c) To provide for just and equitable contribution, if (i) an indemnified
party makes a claim for indemnification pursuant to Section 10(a) or 10(b)
(subject to the limitations thereof) but it is found in a final judicial
determination, not subject to further appeal, that such indemnification may not
be enforced in such case, even though this Agreement expressly provides for
indemnification in such case, or (ii) any indemnified or indemnifying party
seeks contribution under the Securities Act, the Exchange Act or otherwise, then
the Company (including for this purpose any contribution made by or on behalf of
any director of the Company, any officer of the Company who signed any such
registration statement, any controlling person of the Company, and its or their
respective counsel), as one entity, and Parent (including for this purpose any
contribution by or on behalf of an indemnified party), as a second entity, shall
contribute to the losses, liabilities, claims, damages, and expenses whatsoever
to which any of them may be subject, on the basis of relevant equitable
considerations such as the relative fault of the Company and Parent in
connection with the facts which resulted in such losses, liabilities, claims,
damages, and expenses. The relative fault, in the case of an untrue statement,
alleged untrue statement, omission, or alleged omission, shall be determined by,
among other things, whether such statement, alleged statement, omission, or
alleged omission relates to information supplied by the Company or by Parent,
and the parties' relative intent, knowledge, access to information, and
opportunity to correct or prevent such statement, alleged statement, omission,
or


                                      A-2-8
<PAGE>

alleged omission. The Company and Parent agree that it would be unjust and
inequitable if the respective obligations of the Company and Parent for
contribution were determined by pro rata or per capita allocation of the
aggregate losses, liabilities, claims, damages, and expenses (even if Parent and
the other indemnified parties were treated as one entity for such purpose) or by
any other method of allocation that does not reflect the equitable
considerations referred to in this Section 10(c). In no case shall Parent be
responsible for a portion of the contribution obligation in excess of its pro
rata share based on the number of shares of Company Common Stock owned (or which
would be owned upon exercise of all Registrable Securities) by it and included
in such registration as compared to the number of shares of Company Common Stock
owned (or which would be owned upon exercise of all Registrable Securities) by
all persons and included in such registration. No person guilty of a fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any person who is not guilty of such
fraudulent misrepresentation. For purposes of this Section 10(c), each person,
if any, who controls Parent within the meaning of Section 15 of the Securities
Act or Section 20(a) of the Exchange Act and each officer, director, partner,
employee, agent, and counsel of Parent or control person shall have the same
rights to contribution as Parent or control person and each person, if any, who
controls the Company within the meaning of Section 15 of the Securities Act or
Section 20(a) of the Exchange Act, each officer of the Company who shall have
signed any such registration statement, each director of the Company, and its or
their respective counsel shall have the same rights to contribution as the
Company, subject in each case to the provision of this Section 10(c). Anything
in this Section 10(c) to the contrary notwithstanding, no party shall be liable
for contribution with respect to the settlement of any claim or action effected
without its written consent, which consent shall not be unreasonably withheld.
This Section 10(c) is intended to supersede any right to contribution under the
Securities Act, the Exchange Act or otherwise.

     11. Termination; Extension. This Agreement shall terminate upon the
Effective Time (as that term is defined in the Merger Agreement) or upon
termination of the Merger Agreement other than as described in Section 2 hereof.
Notwithstanding anything to the contrary in this Agreement, in the event that
Parent is at any time prohibited from exercising the Option as a result of any
actions by the Federal Trade Commission or the Department of Justice in
connection with the Hart-Scott-Rodino Antitrust Improvements Act, then this
Agreement shall not terminate until the earlier of (i) 30 days from the date
such prohibition is removed by the Federal Trade Commission or the Department of
Justice, or (ii) six months after the date Parent's right to exercise the Option
would otherwise have terminated.

     12. Miscellaneous

        (a) No Waiver. The failure of any party to exercise any right, power or
remedy under this Agreement or otherwise available in respect of this Agreement
at law or in equity, or to insist upon compliance by any other party with that
party's obligations under this Agreement, shall not constitute a waiver of any
right to exercise any such or other right, power or remedy or to demand such
compliance.

        (b) Notices. All notices and other communications hereunder shall be in
writing and shall be delivered personally or by next-day courier or telecopied
with confirmation of receipt, to the parties at the addresses specified below
(or at such other address for a party as shall be specified by like notice;
provided that notices of a change of address shall be effective only upon
receipt thereof). Any such notice shall be effective upon receipt, if personally
delivered or telecopied, or one day after delivery to a courier for next-day
delivery.

       (i) If to Parent, to:

             Celgene Corporation
             7 Powder Horn Drive
             Warren, NJ 07059
             Fax: (732) 805-3931

             with a copy to:

                                      A-2-9
<PAGE>

             Proskauer Rose LLP
             1585 Broadway
             New York, New York 10036
             Attention: Robert A. Cantone, Esq.

       (ii) if to the Company, to:
              Signal Pharmaceuticals, Inc.
              5555 Oberlin Drive
              San Diego, CA 92121
              Fax:


              Attention:

              with a copy to:

             Cooley Godward LLP
             4365 Executive Drive, Suite 1100
             San Diego, CA 92121
             Fax: (858) 453-3555


             Attention: L. Kay Chandler, Esq.


        (c) Descriptive Headings; Interpretation. The headings contained in this
Agreement are for reference purposes only and shall not affect in way the
meaning or interpretation of this Agreement. References in this Agreement to
Sections and Schedules mean a Section or Schedule of this Agreement unless
otherwise indicated. The terms "beneficially own" and "beneficial owner" with
respect to any securities shall have the same meaning as in, and shall be
determined in accordance with, Rule 13d-3 under the Securities Exchange Act of
1934.

        (d) Entire Agreement; Assignment. This Agreement (including the schedule
and other documents and instruments referred to herein), together with the
Merger Agreement, constitute the entire agreement and supersede all other prior
agreements and understandings, both written and oral, among the parties or any
of them, with respect to the subject matter hereof. Except as otherwise
expressly provided herein, this Agreement is not intended to confer upon any
person not a party hereto any rights or remedies hereunder. Except as otherwise
expressly provided herein, this Agreement shall not be assigned by operation of
law or otherwise; provided that Parent may assign its rights and obligations
hereunder to a direct or indirect subsidiary of Parent, but no such assignment
shall relieve Parent or Sub, as the case may be, of its obligations hereunder.

        (e) Injunctive Relief; Remedies Cumulative.

            (i) Parent, on the one hand, and the Company, on the other hand,
acknowledge that the other party will be irreparably harmed and that there will
be no adequate remedy at law for a violation of any of the covenants or
agreements of such party that are contained in this Agreement. It is accordingly
agreed that, in addition to any other remedies that may be available to the
non-breaching party upon the breach by any other party of such covenants and
agreements, the non-breaching party shall have the right to obtain injunctive
relief to restrain any breach or threatened breach of such covenants or
agreements or otherwise to obtain specific performance of any of such covenants
or agreements.


            (ii) No remedy conferred upon or reserved to any party herein is
intended to be exclusive of any other remedy and every remedy shall be
cumulative and in addition to every other remedy herein or now or hereafter
existing at law, in equity or by statute.


        (f) Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of California without giving effect to the
provisions thereof relating to conflicts of laws.


                                     A-2-10
<PAGE>

        (g) Effect of Partial Invalidity. Whenever possible, each provision of
this Agreement shall be construed in such a manner as to be effective and valid
under applicable law. If any provision of this Agreement or the application
thereof to any party or circumstance shall be prohibited by or invalid under
applicable law, such provisions shall be ineffective to the extent of such
prohibition without invalidating the remainder of such provision or any other
provisions of this Agreement or the application of such provision to the other
party or other circumstances.

        (h) Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original but all of which
shall constitute one and the same agreement.

     IN WITNESS WHEREOF, this Agreement has been executed by the parties as of
the date first above written.

                                        SIGNAL PHARMACEUTICALS, INC.





                                      By:-------------------------------------
                                         Authorized Officer





                                        CELGENE CORPORATION





                                      By:-------------------------------------
                                         Authorized Officer

                                     A-2-11
<PAGE>

                                                                     EXHIBIT B-1



  FORM OF TAX REPRESENTATION LETTER TO BE DELIVERED BY PARENT AND MERGER SUB



Cooley Godward, LLP                           Proskauer, Rose LLP
4365 Executive Drive, Ste. 1100               1585 Broadway
San Diego, CA 92121-2128                      New York, NY 10036


          RE: MERGER PURSUANT TO THE AGREEMENT AND PLAN OF MERGER, INCLUDING
              EXHIBITS AND SCHEDULES THERETO (THE "MERGER AGREEMENT") DATED AS
              OF JUNE 29, 2000, BY AND AMONG CELGENE CORPORATION, A DELAWARE
              CORPORATION ("PARENT"); CELGENE ACQUISITION CORP., A CALIFORNIA
              CORPORATION ("MERGER SUB"); AND SIGNAL PHARMACEUTICALS, INC., A
              CALIFORNIA CORPORATION (THE "COMPANY")

Ladies and Gentlemen:

     This letter is supplied to you in connection with your rendering of
opinions rega.rding certain federal income tax consequences of the above
captioned merger (the "Merger"). Unless otherwise indicated, capitalized terms
not defined herein have the meanings set forth in the Merger Agreement.

     After consulting with their counsel and auditors regarding the meaning of
and factual support for the following representations, the undersigned hereby
certify and represent that the following facts are now true and will continue to
be true through the Effective Time and thereafter where relevant:

     1. Pursuant to the Merger, Merger Sub will merge with and into the Company,
and the Company will acquire all of the assets and liabilities of Merger Sub. At
least ninety percent (90%) of the fair market value of the net assets and at
least seventy percent (70%) of the fair market value of the gross assets held by
the Company immediately prior to the Merger and at least ninety percent (90%) of
the fair market value of the net assets and at least seventy percent (70%) of
the fair market value of the gross assets held by Merger Sub immediately prior
to the Merger will be held by the Company after the Merger. For the purpose of
determining the percentage of the Company's and Merger Sub's net and gross
assets held by the Company immediately following the Merger, the following
assets will be treated as property held by the Company or Merger Sub, as the
case may be, immediately prior to the Merger but not by the Company subsequent
to the Merger: (i) assets disposed of by the Company or Merger Sub (other than
assets transferred by Merger Sub to the Company in the Merger) prior to or
subsequent to the Merger and in contemplation thereof (including without
limitation any asset disposed of by the Company or Merger Sub, other than in the
ordinary course of business, pursuant to a plan or intent existing during the
period ending at the Effective Time and beginning with the commencement of
negotiations (whether formal or informal) with the Company regarding the Merger
(the "Pre-Merger Period")), (ii) assets used by the Company or Merger Sub to pay
expenses or liabilities in connection with the Merger, (iii) assets used by the
Company or Merger Sub to make payments to Company stockholders perfecting
appraisal rights or in lieu of fractional shares of Parent Common Stock and (iv)
assets used by the Company or Merger Sub to make distribution, redemption or
other payments in respect of Company stock or rights to acquire such stock
(including payments treated as such for tax purposes) that are made in
contemplation of the Merger or related thereto;

     2. The Merger is being undertaken for business reasons and not for the
purpose of tax avoidance;

     3. Prior to the Merger, Parent will be in "Control" of Merger Sub as
defined in Section 368(c) of the Internal Revenue Code of 1986, as amended (the
"Code"). As used herein, "Control" of a corporation shall consist of direct
ownership of stock possessing at least eighty percent (80%) of the total
combined voting power of all classes of stock entitled to vote and at lease
eighty percent (80%) of the total number of shares of each other class of stock
of the corporation. For purposes of

<PAGE>

determining Control, a person shall not be considered to own voting stock if
rights to vote such stock (or to restrict or otherwise control the voting of
such stock) are held by a third party (including a voting trust) other than an
agent of such person;

     4. Merger Sub has been formed solely to consummate the Merger and, prior to
the Effective Time, Merger Sub has not conducted and will not conduct any
business activity or other operation of any kind (except for the issuance of its
stock to Parent;

     5. In the Merger, shares of Company stock representing Control of the
Company will be exchanged solely for voting stock of Parent;

     6. Parent has no plan or intention to cause the Company to issue additional
shares of stock after the Merger or take any other action that would result in
Parent losing Control of the Company;

     7. Except for transfers described in both Section 368(a)(2)(C) of the Code,
and Treasury Regulation Section 1.368-2(k), Parent has no current plan or
intention to (i) liquidate the Company; (ii) merger the Company with or into
another corporation (including Parent or its affiliates); (iii) sell, distribute
or otherwise dispose of Company stock; or (iv) sell or otherwise dispose of or
cause the Company to sell or otherwise dispose of, any of the Company's assets
(or any assets acquired from Merger Sub) except for dispositions made in the
ordinary course of business or payment of expenses incurred by the Company
pursuant to the Merger;

     8. No liabilities of any person will be assumed by Parent or the Company as
a part of the Merger;

     9. Parent will cause the Company to continue its historic business or use a
significant portion of its historic business assets in a business following the
Merger;

     10. Neither Parent nor any current or former affiliate of Parent owns, or
has owned during the past five (5) years, directly or indirectly, any shares of
Company stock, or the right to acquire or vote any such shares (except such
rights as are granted in the Merger Agreement);

     11. Neither Parent nor Merger Sub is an investment company within the
meaning of Sections 368(a)(2)(F)(iii) and (iv) of the Code;

     12. Parent has no plan or intention to reacquire any of its stock issued in
the Merger. Except for repurchases or redemptions of Parent Common Stock that:
(i) are consistent with past practices and pursuant to pre-existing, seasoned
and systematic purchase programs that were not created or modified in connection
with the Merger; or (ii) are made in connection with the termination of
employees in the ordinary course of business, neither the Company nor Parent
(nor any agent of Parent) nor any "related person" of the Company or Parent (as
such term is defined by Treasury Regulations Section 1.368-1(e)3)) will
repurchase or redeem any of the Parent Common Stock to be issued to the
stockholders of the Company in connection with the Merger;

     13. Except with respect to payments of cash to stockholders of the Company
perfecting appraisal rights or in lieu of fractional shares of Parent Common
Stock, one hundred percent (100%) of the stock of the Company outstanding
immediately prior to the Merger will be exchanged solely for Parent Common;

     14. The total fair market value of all consideration other than Parent
Common Stock received by stockholders of the Company in the Merger (including,
without limitation, cash paid to stockholders of the Company perfecting
appraisal rights or in lieu of fractional shares of Parent Common Stock) will be
less than ten percent (10%) of the aggregate fair market value of stock of the
Company outstanding immediately prior to the Merger;

     15. Neither Parent nor Merger Sub is under the jurisdiction of court in a
Title 11 or similar case within the meaning of Section 368(a)3(A) of the Code;

     16. The payment of cash in lieu of fractional shares of Parent Common Stock
is solely for the purpose of avoiding the expense and inconvenience to Parent of
issuing fractional shares and does not represent separately bargained-for
consideration. The total cash consideration that will be paid in


                                      B-1-2
<PAGE>

the Merger to Company stockholders in lieu of fractional shares of Parent Common
Stock will not exceed one percent (1%) of the total consideration that will be
issued in the Merger to Company stockholders in exchange for their shares of
Company stock. The fractional share interests of each Company stockholder will
be aggregated and no Company stockholder will receive cash in an amount greater
than the value of one full share of Parent Common Stock;

     17. At the Effective Time, the fair market value of the Parent Common Stock
received by each Company stockholder will be approximately equal to the fair
market value of the Company stock surrendered in exchange thereof, and the
aggregate consideration received by Company stockholders, as described in
Section of the Merger Agreement, in exchange for their Company stock will be
approximately equal to the fair market value of all of the outstanding shares of
Company stock immediately prior to the Merger;

     18. Parent, Merger Sub, the Company and the stockholders of the Company
will each pay separately its or their own expenses in connection with the Merger
(other than expenses directly related to the transaction within the guidelines
set forth in Revenue Ruling 73-59, 1973-1 C.B. 187);

     19. There is no intercorporate indebtedness existing between Parent and the
Company or between Merger Sub and the Company;

     20. Parent will assume no liabilities of the Company or any Company
stockholder in connection with the Merger;

     21. The terms of the Merger Agreement and all other agreements entered into
in connection therewith are the product of arm's length negotiations;

     22. None of the payments received by any stockholder-employees or
stockholder-independent contractors of the Company that are designated as
compensation are actually separate consideration for, or allocable to, any of
their shares of Company stock; none of the shares of Parent Common Stock
received by any stockholder-employees or stockholder-independent contractors of
the Company in exchange for shares of Company stock are actually separate
consideration for, or allocable to, any employment agreement, consulting
agreement, covenant not to compete or release; and the compensation paid to any
stockholder-employees or stockholder-independent contractors of the Company will
be for services actually rendered and will be commensurate with amounts paid to
third parties bargaining at arm's length for similar services;

     23. With respect to each instance, if any, in which shares of Company stock
have been purchased by a stockholder of Parent (a "Stockholder") during the
Pre-Merger Period (a "Stock Purchase"): (i) the Stock Purchase was not made by
such Stockholder as a representative, or for the benefit, of Parent; (ii) the
purchase price paid by such Stockholder pursuant to the Stock Purchase was not
and will not be advanced, and was not and will not be reimbursed, either
directly or indirectly, by Parent; (iii) at no times was such Stockholder or any
other party required or obligated to surrender to Parent Company stock acquired
in the Stock Purchase, and neither such Stockholder nor any other party will be
required to surrender to Parent the Parent Common Stock for which such shares of
Company stock will be exchanged in the Merger; and (iv) the Stock Purchase was
not a formal or informal condition to consummation of the Merger;

     24. Following the Merger, Parent, Merger Sub and the Company will comply
with the record-keeping and information filing requirements of Treasury
Regulations Section 1.368-3;

     25. The Merger will be consummated in compliance with the material terms of
the Merger Agreement, none of the material terms and conditions therein have
been waived or modified, and Parent has no plan or intention to waive or modify
any such material terms and conditions;

     26. Each of the representations made by Parent and Merger Sub in the Merger
Agreement and any other documents associated therewith is true and accurate; and

     27. The undersigned officer of each of Parent and Merger Sub is authorized
to make all of the certifications and representations on behalf of Parent and
Merger Sub, respectively, set forth herein.


                                      B-1-3
<PAGE>

The undersigned recognize that (i) your opinions will be based on, among other
things, the accuracy of the representations set forth herein and on the
statements contained in the Merger Agreement and documents related thereto, (ii)
your opinions will be subject to certain limitations and qualifications
including that they may not be relied upon if any such representations are not
accurate in all material respects, or if any of the covenants or obligations set
forth in the Merger Agreement are not satisfied in all material respects and
(iii) your opinions will not address any tax consequences of the Merger or any
action taken in connection therewith except as expressly set forth in such
opinions.

     Parent and Merger Sub undertake to inform you immediately should any of the
foregoing statements or representations become untrue, incorrect or incomplete
in any respect on or prior to the Effective Time.

                                        Very truly yours,


                                        CELGENE CORPORATION, a Delaware
                                        Corporation


                                        By:
                                           -----------------------------------


                                        Printed  Name:
                                                      ------------------------


                                        Title:
                                              --------------------------------


                                        CELGENE ACQUISITION  CORP., a California
                                        Corporation


                                        By:
                                           -------------------------------------


                                        Printed Name:
                                                     ---------------------------


                                        Title:
                                              ----------------------------------




                                      B-1-4
<PAGE>

                                                                    EXHIBIT B-2


         FORM OF TAX REPRESENTATION LETTER TO BE DELIVERED BY COMPANY


Cooley Godward LLP                                 Proskauer, Rose LLP
4365 Executive Drive, Ste. 1100                    1585 Broadway
San Diego, CA 92121-2128                           New York, NY 10036


        RE:  MERGER PURSUANT TO THE AGREEMENT AND PLAN OF MERGER, INCLUDING
             EXHIBITS AND SCHEDULES THERETO (THE "MERGER AGREEMENT") DATED AS OF
             JUNE 29, 2000, BY AND AMONG CELGENE CORPORATION, A DELAWARE
             CORPORATION ("PARENT"); CELGENE ACQUISITION CORP., A CALIFORNIA
             CORPORATION ("MERGER SUB"); AND SIGNAL PHARMACEUTICALS, INC., A
             CALIFORNIA CORPORATION (THE "COMPANY").

Ladies and Gentlemen:

     This letter is supplied to you in connection with your rendering of
opinions regarding certain federal income tax consequences of the above
captioned merger (the "Merger"). Unless otherwise indicated, capitalized terms
not defined herein have the meanings set forth in the Merger Agreement.

     After consulting with its counsel and auditors regarding the meaning of and
factual support for the following representations, the undersigned hereby
certifies and represents that the following facts are now true and will continue
to be true through the Effective Time and thereafter where relevant:

     1. Pursuant to the Merger, Merger Sub will merge with and into the Company,
and the Company will acquire all of the assets and liabilities of Merger Sub. At
least ninety percent (90%) of the fair market value of the net assets and at
least seventy percent (70%) of the fair market value of the gross assets held by
the Company immediately prior to the Merger, and at least ninety percent (90%)
of the fair market value of the net assets and at least seventy percent (70%) of
the fair market value of the gross assets held by Merger Sub immediately prior
to the Merger will be held by the Company after the Merger. For the purpose of
determining the percentage of net and gross assets held by the Company
immediately following the Merger, the following assets will be treated as
property held by the Company or Merger Sub, as the case may be, immediately
prior to the Merger but not by the Company subsequent to the Merger; (i) assets
disposed of by the Company or Merger Sub (other than assets transferred by
Merger Sub to the Company in the Merger) prior to or subsequent to the Merger
and in contemplation thereof (including, without limitation, any asset disposed
of by the Company or Merger Sub, other than in the ordinary course of business,
pursuant to a plan or intent existing during the period ending at the Effective
Time and beginning with the commencement of negotiations (whether formal or
informal) with Parent regarding the Merger (the "Pre-Merger Period")), (ii)
assets used by the Company or Merger Sub to pay expenses or liabilities incurred
in connection with the Merger, (iii) assets used by the Company or Merger Sub to
make payments to Company stockholders perfecting appraisal rights or in lieu of
fractional shares of Parent Common Stock, and (iv) assets used by the Company or
Merger Sub to make distribution, redemption or other payments in respect of
Company stock or rights to acquire such stock (including payments treated as
such for tax purposes) that are made in contemplation of the Merger or related
thereto;

     2. The Company has made no transfer of any of its assets (including any
distribution of assets with respect to, or in redemption of, stock) in
contemplation of the Merger or during the Pre-Merger Period other than (i) in
the ordinary course of business and (ii) payments for expenses incurred in
connection with the Merger;

     3. The Merger is being undertaken for business reasons and not for the
purpose of tax avoidance;

     4. At the Effective Time, the Company will have no stock or other equity
interests outstanding other than those set forth in Section ___ of the Merger
Agreement and will not have any warrants, options, convertible securities or any
other type of right outstanding pursuant to which any person could

<PAGE>

acquire any shares of Company stock or any other equity interest in the Company
that, if exercised or converted, could affect Parent's acquisition or retention
of "Control" of the Company (as defined in Section 368(c) of the Internal
Revenue Code of 1986, as amended (the "Code")). As used herein, "Control" of a
corporation shall consist of direct ownership of stock possessing at least
eighty percent (80%) of the total number of shares of each other class of stock
of the corporation. For purposes of determining Control, a person shall not be
considered to own voting stock if rights to vote such stock (or to restrict or
otherwise control the voting of such stock) are held by a third party (including
a voting trust) other than an agent of such person;

     5. In the Merger, shares of Company stock representing Control of the
Company will be exchanged solely for voting stock of Parent. For purposes of
this certificate, shares of Company stock exchanged in the Merger for cash and
other property (including, without limitation, cash paid to Company stockholders
perfecting appraisal rights or in lieu of fractional shares of Parent Common
Stock) will be treated as shares of Company stock outstanding on the date of the
Merger but not exchanged for voting stock of Parent;

     6. The liabilities of the Company have been incurred by the Company in the
ordinary course of its business;

     7. The Company does not and will not at the Effective Time have any
liability (i) to any Company stockholder incurred in exchange for cash or other
asset transferred to the Company, or (ii) to Parent or Merger Sub;

     8. No Company stockholder has guaranteed any Company indebtedness that is
currently outstanding or will be outstanding at the Effective Time;


     9. The fair market value of the Company's assets will, at the Effective
Time, exceed the aggregate liabilities of the Company plus the amount of
liabilities, if any, to which such assets are subject;


     10. Other than shares of Company stock or Company Options issued as
compensation to present or former service providers (including, without
limitation, employees and directors) of the Company in the ordinary course of
business, no issuances of Company stock or rights to acquire Company stock have
occurred or will occur during the Pre-Merger Period other than pursuant to
options, warrants or agreements outstanding prior to the Pre-Merger Period or as
otherwise specifically identified in the Merger Agreement;


     11. Cash or other property paid to employees of the Company during the
Pre-Merger Period has been or will be in the ordinary course of business or
pursuant to agreements entered into prior to the Pre-Merger Period;


     12. The Company is not and will not be at the Effective Time an "investment
company" within the meaning of Section 368(a)(2)(F)(iii) and (iv) of the Code;


     13. The Company is not under the jurisdiction of a court in a Title 11 or
similar case within the meaning of Section 368(a)(3)(A) of the Code;


     14. The Company (i) has not redeemed and will not redeem any of its stock
prior to and in connection with the Merger, and (ii) has not made and will not
make any extraordinary distributions (within the meaning of Section
1.368-1T(e)(1) of the Treasury Regulations) with respect to its stock prior to
and in connection with the Merger. For the purposes of this representation,
extraordinary distributions will not include periodic dividends that are
consistent with the Company's historic dividend practices;


     15. No person related to the Company (within the meaning of Section
1.368-1(e)(3) of the Treasury Regulations, without regard to Section
1.368-1(e)(3)(i)(A)) has acquired or will acquire any stock of the Company prior
to and in connection with the Merger;


     16. Except with respect to payments of cash to Company stockholders
perfecting appraisal rights or in lieu of fractional shares of Parent Common
Stock, one hundred percent (100%) of the Company stock outstanding immediately
prior to the Merger will be exchanged solely for Parent voting stock. The


                                      B-2-2
<PAGE>

total market value of all consideration other than shares of Parent Common Stock
that will be paid for shares of Company stock exchanged pursuant to the Merger
Agreement will be less than ten percent (10%) of the aggregate fair market value
of the shares of Company stock outstanding immediately prior to the Merger;


     17. At the Effective Time, the fair market value of the Parent Common Stock
received by each Company stockholder will be approximately equal to the fair
market value of the Company stock surrendered in exchange therefor, and the
aggregate consideration received by the Company stockholders, as described in
Section __ of the Merger Agreement, in exchange for their Company stock will be
approximately equal to the fair market of all of the outstanding shares of
Company stock immediately prior to the Merger;


     18. Parent, Merger Sub, the Company and the stockholders of the Company
will each pay separately its or their own expenses in connection with the Merger
(other than expenses directly related to the transaction within the guidelines
set forth in Revenue Ruling 73-54, 1973-1, C.B. 187):


     19. The terms of the Merger Agreement and all other agreements entered into
in connection therewith are the product of arm's-length negotiations;


     20. None of the payments received by any stockholder-employees or
stockholder-independent contractors of the Company that are designated as
compensation are actually separate consideration for, or allocable to, any of
their shares of Company stock; none of the shares of Parent Common Stock
received by any stockholder-employees or stockholder-independent contractors of
the Company in exchange for shares of Company stock are actually separate
consideration for, or allocable to, any employment agreement, consulting
agreement covenant not to compete or release; and the compensation paid to any
stockholder-employees or stockholder-independent contractors of the Company will
be for services actually rendered and will be commensurate with amounts paid to
third parties bargaining at arm's length for similar services;


     21. No direct or indirect subsidiary (whether or not incorporated) of the
Company owns any share of Company stock;


     22. The Company, to its best knowledge and belief, will continue its
historic business or use a significant portion of its historic business assets
in a business following the Merger;


     23. There is no intercorporate indebtedness existing between Parent and the
Company or between Merger Sub and the Company;


     24. The payment of cash in lieu of fractional shares of Parent Common Stock
in connection with the consummation of the Merger is solely for the purpose of
avoiding the expense and inconvenience to Parent of issuing fractional shares
and does not represent separately bargained-for consideration. The total cash
consideration that will be paid in the Merger to Company stockholders instead of
issuing fractional shares of Parent Common Stock will not exceed one percent
(1%) of the total consideration that will be issued in the transaction to
Company stockholders in exchange for their stock. The fractional share interests
of each stockholder will be aggregated and no Company stockholder will receive
cash in an amount equal to or greater than the value of one full share of Parent
Common Stock;


     25. With respect to each instance, if any, in which shares of stock of the
Company have been purchased by a stockholder of Parent (a "Stockholder") during
the Pre-Merger Period (a "Stock Purchase"): (i) to the knowledge of the Company
(A) the Stock Purchase was mde by such Stockholder on its own behalf, rather
than as a representative, or for the benefit, of Parent (B) the Stock Purchase
was entered into solely to satisfy the separate interests of such Stockholder
and pursuant to the Stock Purchase was the product of arm's length negotiations;
and (ii) the Stock Purchase was not a formal or informal condition to
consummation of the Merger;


     26. The Merger will be consummated in compliance with the material terms of
the Merger Agreement, none of the material terms and conditions therein have
been waived or modified, and the Company has no plan or intention to waive or
modify any such material terms and conditions;


                                      B-2-3
<PAGE>

     27. Each of the representations made by the Company in the Merger Agreement
and any other documents associated therewith is true and accurate; and

     28. The undersigned officer is authorized to make all of the certifications
and representations on behalf of the Company set forth herein.

     The undersigned recognizes that (i) your opinions will be based on, among
other things, the accuracy of the representations set forth herein and on the
statements contained in the Merger Agreement and documents related thereto, (ii)
your opinions will be subject to certain limitations and qualifications
including that they may not be relied upon if any such representations are not
accurate in all material respects, or if any of the covenants and obligations
set forth in the Merger Agreement are not satisfied in all material respects and
(iii) your opinions will not address any tax consequences of the Merger or any
action taken in connection therewith except as expressly set forth in such
opinions.

     Notwithstanding anything herein to the contrary, the undersigned makes no
representations regarding any actions or conduct of the Company pursuant to
Parent's exercise of control over the Company after the Merger.

     The Company undertakes to inform you immediately should any of the
foregoing statements or representations become untrue, incorrect or incomplete
in any respect on or prior to the Effective Time.


                                    Very truly yours,


                                    SIGNAL  PHARMACEUTICALS, INC., a California
                                    Corporation



                                     By:
                                        ----------------------------------------


                                     Printed Name:
                                                  ------------------------------


                                     Title:
                                           -------------------------------------





                                      B-2-4
<PAGE>

                                  EXHIBIT C TO THE AGREEMENT AND PLAN OF MERGER


                               AFFILIATE AGREEMENT

     THIS AFFILIATE AGREEMENT ("Affiliate Agreement") is being executed and
delivered as of ___________, 2000 by __________________________ ("Stockholder")
in favor of and for the benefit of Celgene Corporation, a Delaware corporation
("Parent").



                                    RECITALS

     A. Stockholder is a stockholder of, and is an officer and/or director of
Sunset, Inc., a California corporation (the "Company").

     B. Parent, the Company and Celgene Acquisition Corp., a California
corporation and wholly-owned subsidiary of Parent ("Sub"), have entered into an
Agreement and Plan of Merger dated as of ________, 2000 (the "Merger
Agreement"), providing for the merger of Sub into the Company (the "Merger").
The Merger Agreement contemplates that, upon consummation of the Merger, the
holders of the Company's Common Stock (the "Company Common Stock"), including
holders of the Company's Preferred Stock (the "Company Preferred Stock") which
is to be converted immediately prior to the Merger, will be entitled to receive
shares of Parent's Common Stock, par value $.01 per share ("Parent Common
Stock"), for such shares of Company Common Stock.

     C. Stockholder understands that the Parent Common Stock to be issued in the
Merger will be issued pursuant to a registration statement on Form S-4, and that
Stockholder may be deemed an "affiliate" of Parent as such term is defined for
purposes of paragraphs (c) and (d) of Rule 145 under the Securities Act of 1933,
as amended (the "Securities Act").



                                    AGREEMENT

     Stockholder, intending to be legally bound, agrees as follows:

     1. REPRESENTATIONS AND WARRANTIES OF STOCKHOLDERS. Stockholder represents
and warrants to Parent as follows:

     a. Stockholder is the holder and "beneficial owner" (as defined in Rule
13d-3 under the Securities Exchange Act of 1934, as amended) of the number of
outstanding shares of common stock of the Company set forth beneath
Stockholder's signature on the signature page hereof (the "Company Shares"), and
Stockholder has good and valid title to the Company Shares, free and clear of
any liens, pledges, security interests, adverse claims, equities, options,
proxies, charges, encumbrances or restrictions of any nature. Stockholder has
the sole right to vote and to dispose of the Company Shares.

     b. Stockholder is the holder of options to purchase the number of shares of
common stock of the Company set forth beneath Stockholder's signature on the
signature page hereof (the "Company Options"), and Stockholder has good and
valid title to the Company Options, free and clear of any liens, pledges,
security interests, adverse claims, equities, options, proxies, charges,
encumbrances or restrictions of any nature.

     c. Stockholder does not own, of record or beneficially, directly or
indirectly, any securities of the Company other than the Company Shares and the
Company Options.

     d. Stockholder has carefully read this Affiliate Agreement and, to the
extent Stockholder felt necessary, has discussed with counsel the limitations
imposed on Stockholder's ability to sell, transfer or otherwise dispose of the
shares of Parent Common Stock that Stockholder is to receive in the Merger (the
"Parent Shares"). Stockholder fully understands the limitations this Affiliate
Agreement places upon Stockholder's ability to sell, transfer or otherwise
dispose of securities of Parent.

     2. PROHIBITIONS AGAINST TRANSFER.
<PAGE>

     a. Stockholder shall not sell, transfer, or otherwise dispose of any Parent
Shares until after the publication (the "Publication Date") of financial
statements reflecting the combined operating results of the Company and Parent
for a period of not less than 30 days from and after the Effective Time (as such
term is defined in the Merger Agreement).

     b. From and after the Publication Date Stockholder shall not effect any
sale, transfer or other disposition of any Parent Shares unless:

        (i) such sale, transfer or other disposition is effected pursuant to an
effective registration statement under the Securities Act;

        (ii) such sale, transfer or other disposition is made in conformity with
the requirements of Rule 145 under the Securities Act, as evidenced by a
broker's letter and a representation letter executed by Stockholder
(satisfactory in form and content to Parent) stating that such requirements have
been met;

        (iii) counsel reasonably satisfactory to Parent shall have advised
Parent in a written opinion letter (satisfactory in form and content to Parent),
upon which Parent may rely, that such sale, transfer or other disposition will
be exempt from the registration requirements of the Securities Act; or

        (iv) an authorized representative of the Securities and Exchange
Commission ("SEC") shall have rendered written advice to Stockholder to the
effect that the SEC would take no action, or that the staff of the SEC would not
recommend that the SEC take action, with respect to such sale, transfer or other
disposition, and a copy of such written advice and all other related
communications with the SEC shall have been delivered to Parent.

     3. STOP TRANSFER INSTRUCTIONS; LEGEND.

     Stockholder acknowledges and agrees that (a) stop transfer instructions
will be given to Parent's transfer agent with respect to the Parent Shares, and
(b) each certificate representing any of such Parent Shares shall bear a legend
identical or similar in effect to the following legend (together with any other
legend or legends required by applicable state securities laws or otherwise):

        "THE SHARES REPRESENTED BY THIS CERTIFICATE WERE ISSUED IN A TRANSACTION
        TO WHICH RULE 145(d) OF THE SECURITIES ACT OF 1933 APPLIES AND MAY NOT
        BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, ASSIGNED, PLEDGED OR
        HYPOTHECATED EXCEPT IN ACCORDANCE WITH THE PROVISIONS OF SUCH RULE AND
        IN ACCORDANCE WITH THE TERMS OF AN AGREEMENT DATED AS OF __________,
        2000, BETWEEN THE REGISTERED HOLDER HEREOF AND THE ISSUER, A COPY OF
        WHICH IS ON FILE AT THE PRINCIPAL OFFICES OF THE ISSUER."

     4. INDEPENDENCE OF OBLIGATIONS. The covenants and obligations of
Stockholder set forth in this Affiliate Agreement shall be construed as
independent of any other agreement or arrangement between Stockholder, on the
one hand, and the Company or Parent, on the other. The existence of any claim or
cause of action by Stockholder against the Company or Parent shall not
constitute a defense to the enforcement of any of such covenants or obligations
against Stockholder.

     5. SPECIFIC PERFORMANCE. Stockholder agrees that in the event of any breach
or threatened breach by Stockholder of any covenant, obligation or other
provision contained in this Affiliate Agreement, Parent shall be entitled (in
addition to any other remedy that may be available to Parent) to: (a) a decree
or order of specific performance or mandamus to enforce the observance and
performance of such covenant, obligation or other provision; and (b) an
injunction restraining such breach or threatened breach. Stockholder further
agrees that neither Parent nor any other person or entity shall be required to
obtain, furnish or post any bond or similar instrument in connection with or as
a condition to obtaining any remedy referred to in this Section 5, and
Stockholder irrevocably waives any right he may have to require the obtaining,
furnishing or posting of any such bond or similar instrument.


                                       C-2
<PAGE>

     6. OTHER AGREEMENTS. Nothing in this Affiliate Agreement shall limit any of
the rights or remedies of Parent under the Merger Agreement, or any of the
rights or remedies of Parent or any of the obligations of Stockholder under any
agreement between Stockholder and Parent or any certificate or instrument
executed by Stockholder in favor of Parent; and nothing in the Merger Agreement
or in any other agreement, certificate or instrument shall limit any of the
rights or remedies of Parent or any of the obligations of Stockholder under this
Affiliate Agreement.


     7. NOTICES. Any notice or other communication required or permitted to be
delivered to Stockholder or Parent under this Affiliate Agreement shall be in
writing and shall be deemed properly delivered, given and received when
delivered to the address or facsimile telephone number set forth beneath the
name of such party below (or to such other address or facsimile telephone number
as such party shall have specified in a written notice given to the other
party):


     IF TO PARENT:


      Celgene Corporation


       -------------------------------
       -------------------------------
       Attn:
       Facsimile:


     IF TO STOCKHOLDER:


       -------------------------------


       -------------------------------
       Attn:
       Facsimile:


     8. SEVERABILITY. If any provision of this Affiliate Agreement or any part
of any such provision is held under any circumstances to be invalid or
unenforceable in any jurisdiction, then (a) such provision or part thereof
shall, with respect to such circumstances and in such jurisdiction, be deemed
amended to conform to applicable laws so as to be valid and enforceable to the
fullest possible extent, (b) the invalidity or unenforceability of such
provision or part thereof under such circumstances and in such jurisdiction
shall not affect the validity or enforceability of such provision or part
thereof under any other circumstances or in any other jurisdiction, and (c) the
invalidity or unenforceability of the remainder of such provision or the
validity or enforceability of any other provision of this Affiliate Agreement.
Each provision of this Affiliate Agreement is separable from every other
provision of this Affiliate Agreement, and each part of each provision of this
Affiliate Agreement is separable from every other part of such provision.


     9. APPLICABLE LAW. THIS AFFILIATE AGREEMENT IS MADE UNDER, AND SHALL BE
CONSTRUED AND ENFORCED IN ACCORDANCE WITH, THE LAWS OF CALIFORNIA APPLICABLE TO
AGREEMENTS MADE AND TO BE PERFORMED SOLELY THEREIN, WITHOUT GIVING EFFECT TO
PRINCIPLES OF CONFLICTS OF LAW.


     10. TERM; WAIVER; TERMINATION. The term of the Agreement shall be for a
period of one year from the effective date of the Merger. No failure on the part
of Parent to exercise any power, right, privilege or remedy under this Affiliate
Agreement, and no delay on the part of Parent in exercising any power, right,
privilege or remedy under this Affiliate Agreement, shall operate as a waiver of
such power, right, privilege or remedy; and no single or partial exercise of any
such power, right, privilege or remedy shall preclude any other or further
exercise thereof or of any other power, right, privilege or remedy. Parent shall
not be deemed to have waived any claim arising out of this Affiliate Agreement,
or any power, right, privilege or remedy under this Affiliate Agreement, unless
the waiver of such claim, power, right, privilege or remedy is expressly set
forth in a written instrument


                                       C-3
<PAGE>

duly executed and delivered on behalf of Parent; and any such waiver shall not
be applicable or have any effect except in the specific instance in which it is
given. If the Merger Agreement is terminated, this Affiliate Agreement shall
thereupon terminate.

     11. CAPTIONS. The captions contained in this Affiliate Agreement are for
convenience of reference only, shall not be deemed to be a part of this
Affiliate Agreement and shall not be referred to in connection with the
construction or interpretation of this Affiliate Agreement.

     12. FURTHER ASSURANCES. Stockholder shall execute and/or cause to be
delivered to Parent such instruments and other documents and shall take such
other actions as Parent may reasonably request to effectuate the intent and
purposes of this Affiliate Agreement.

     13. ENTIRE AGREEMENT. This Affiliate Agreement, the Merger Agreement and
any Stockholder Agreement between Stockholder and Parent collectively set forth
the entire understanding of parent and Stockholder relating to the subject
matter hereof and thereof and supersede all other prior agreements and
understandings between Parent and Stockholder relating to the subject matter
hereof and thereof.

     14. NON-EXCLUSIVITY. The rights and remedies of Parent hereunder are not
exclusive of or limited by any other rights or remedies which Parent may have,
whether at law, in equity, by contract or otherwise, all of which shall be
cumulative (and not alternative).

     15. AMENDMENTS. This Affiliate Agreement may not be amended, modified,
altered or supplemented other than by means of a written instrument duly
executed and delivered on behalf of Parent and Stockholder.

     16. ASSIGNMENT. This Affiliate Agreement and all obligations of Stockholder
hereunder are personal to Stockholder and may not be transferred or delegated by
Stockholder at any time. Parent may freely assign any or all of its rights under
this Affiliate Agreement, in whole or in part, to any other person or entity
without obtaining the consent or approval of Stockholder.

     17. BINDING NATURE. Subject to Section 16, this Affiliate Agreement will
inure to the benefit of Parent and its successors and assigns and will be
binding upon Stockholder and Stockholder's representatives, executors,
administrators, estate, heirs, successors and assigns.

     18. SURVIVAL. Each of the representations, warranties, covenants and
obligations contained in this Affiliate Agreement shall survive the consummation
of the Merger.


                                 [END OF TEXT]

                                       C-4
<PAGE>

   Stockholder has executed this Affiliate Agreement on ____________, 2000.


                                            -------------------------------
                                                  (Signature)



                                            -------------------------------
                                                  (Print Name)



NUMBER OF OUTSTANDING SHARES OF
COMMON STOCK OF THE COMPANY HELD BY STOCKHOLDER:



-------------------------------



NUMBER OF SHARES OF COMMON STOCK OF THE COMPANY SUBJECT TO OPTIONS HELD BY
STOCKHOLDER:



-------------------------------

                                       C-5
<PAGE>

                                                                       EXHIBIT D




June __, 2000



Celgene Corporation
7 Powder Horn Drive
Warren, NJ 07059



Ladies and Gentlemen:


We have acted as counsel for Signal Pharmaceuticals, Inc., a California
corporation (the "Company"), in connection with that certain Agreement and Plan
of Merger dated as of June , 2000 (the "Merger Agreement"), by and among the
Company, Celgene Corporation ("Celgene"), and Cape May Acquisition Corp., a
California corporation and wholly-owned subsidiary of Celgene ("Merger Sub"),
pursuant to which Merger Sub will merge with and into the Company (the
"Merger"). We are rendering this opinion pursuant to Section 8.2(g) of the
Merger Agreement. Except as otherwise defined herein, capitalized terms used but
not defined herein have the respective meanings given to them in the Merger
Agreement.

In connection with this opinion, we have examined and relied upon the
representations and warranties as to factual matters contained in and made
pursuant to the Merger Agreement by the various parties and originals or copies
certified to our satisfaction, of such records, documents, certificates,
opinions, memoranda and other instruments as in our judgment are necessary or
appropriate to enable us to render the opinions expressed below. Where we render
an opinion "to the best of our knowledge" or concerning an item "of which we are
aware" or our opinion otherwise refers to our knowledge, it is based solely upon
(i) an inquiry of attorneys within this firm who perform legal services for the
Company, (ii) receipt of certificates executed by an officer of the Company
covering such matters and (iii) such other investigation, if any, that we
specifically set forth herein.

In rendering this opinion, we have assumed: the genuineness and authenticity of
all signatures on original documents; the authenticity of all documents
submitted to us as originals; the conformity to originals of all documents
submitted to us as copies; the accuracy, completeness and authenticity of
certificates of public officials; and the due authorization, execution and
delivery of all documents (except the due authorization, execution and delivery
of the Merger Agreement by the Company) where authorization, execution and
delivery are prerequisites to the effectiveness of such documents. We have also
assumed: that all individuals executing and delivering documents had the legal
capacity to so execute and deliver; that you have received all documents you
were to receive under the Merger Agreement; that the Merger Agreement is an
obligation binding upon you and Merger Sub; that you and Merger Sub have filed
any required California franchise or income tax returns and have paid any
required California franchise or income taxes; and that there are no extrinsic
agreements or understandings among the parties to the Merger Agreement that
would modify or interpret the terms of the Merger Agreement or the respective
rights or obligations of the parties thereunder.
<PAGE>

Celgene Corporation
June __, 2000
Page Two

Our opinion is expressed only with respect to the federal laws of the United
States of America, the laws of the State of California and the Delaware General
Corporation Law. We express no opinion as to whether the laws of any particular
jurisdiction apply, and no opinion to the extent that the laws of any other
jurisdiction are applicable to the subject matter hereof. We are not rendering
any opinion as to compliance with any fiduciary duty law, antitrust or antifraud
law, rule, or regulation relating to securities or to the sale or issuance
thereof, the voting of securities or disclosure made in connection with the
solicitation of shareholder approval of the Merger. Notwithstanding anything
herein to the contrary, no opinion is given or may be implied as to compliance
with any federal or sate securities laws pertaining to requirements to register
securities or obtain exemptions from such requirements.

With regard to our opinion in paragraph 5 below with respect to any material
default under any of the Company's material agreements, we have relied solely
upon (i) inquiries of officers of the Company; and (ii) an examination of the
Company contracts, agreements or arrangements set forth in Schedule 4.15 of the
Company Disclosure Schedules (the "Material Agreements"); we have made no
further investigation. Furthermore, with respect to the Material Agreements, we
have assumed there are no extrinsic agreements or understandings among the
parties to the Material Agreements that would modify or interpret the terms of
the Material Agreements or the respective rights or obligations of the parties
thereunder.

With regard to our opinion in paragraph 5 below with respect to the violation or
contravention of any governmental statute, rule or regulation, and with regard
to our opinion in paragraph 7 below with respect to registrations and
qualifications with any regulatory authority or governmental body in the United
States, our opinion is limited exclusively to the transactions contemplated by
the Merger Agreement.

On the basis of the foregoing, in reliance thereon and with the foregoing
qualifications, we are of the opinion that:

1. The Company has been duly incorporated and is validly existing as a
corporation in good standing under the laws of the State of California.

2. The Company has the requisite corporate power to own, operate and lease its
property and assets and to conduct its business as it is currently being
conducted. To our knowledge, the Company is qualified as a foreign corporation
to do business and is in good standing in each jurisdiction in the United States
in which the ownership of its property or the conduct of its business requires
such qualification, except where the failure to so qualify would not have a
material adverse effect on the assets, financial condition or operations of the
Company.

3. All corporate action on the part of the Company, its Board of Directors and
its shareholders necessary for the authorization, execution and delivery of the
Merger Agreement by the Company and the performance of the Company's obligations
under the Merger Agreement has been taken. The Merger Agreement has been duly
and validly authorized, executed and delivered by the Company and constitutes a
valid and binding agreement of the Company enforceable against the Company in
accordance with its terms, except as enforcement may be limited by applicable
bankruptcy, insolvency, reorganization, arrangement, moratorium or other similar
laws affecting creditors' rights, and subject to general equity principles and
to limitations on availability of equitable relief, including specific
performance.

4. The authorized capital stock of the Company consists of (i) 37,563,708 shares
of Common Stock, of which shares have been issued and are outstanding
immediately prior to the Closing, and (ii) 24,967,639 shares of Preferred Stock:
(A) 2,626,892 of which have been designated as Series A


                                       D-2
<PAGE>

Celgene Corporation
June __, 2000
Page Three


Preferred shares, all of which are outstanding immediately prior to the Closing;
(B) 2,875,000 of which have been designated Series B Preferred shares, all of
which are outstanding immediately prior to the Closing; (C) 8,791,432 of which
have been designated as Series C Preferred shares, 8,791,432 of which are
outstanding immediately prior to the Closing; (D) 250,000 of which have been
designated Series C-1 Preferred shares, none of which is outstanding immediately
prior to the Closing; (E) 225,000 of which have been designated Series C-2
Preferred shares, none of which is outstanding immediately prior to the Closing;
(F) 732,601 of which have been designated Series D Preferred shares, all of
which are outstanding immediately prior to the Closing; (G) 6,455,493 of which
have been designated as Series E Preferred shares, all of which are outstanding
immediately prior to the Closing; (H) 2,722,513 of which have been designated
Series F Preferred shares, all of which are outstanding immediately prior to the
Closing; and (I) 288,708 of which have been designated as Series F-1 Preferred
shares, all of which are outstanding immediately prior to the Closing. To our
knowledge, except as expressly set forth in the Company Disclosure Schedules,
there are no options, warrants, conversion privileges, or other rights presently
outstanding to purchase any authorized but unissued capital stock of the
Company. There are no voting agreements, co-sale rights or rights of first
refusal applicable to any of the Company's outstanding capital stock under the
Company's articles of incorporation, bylaws or any Material Agreement.

5. The execution, delivery and performance by the Company of the Merger
Agreement and the consummation by the Company of the Merger as provided therein
do not violate any provision of the Company's Articles of Incorporation or
Bylaws, and do not constitute a material default (or give rise to any right of
termination, cancellation or acceleration) under any material provision of any
Material Agreement and do not violate or contravene (A) any governmental
statute, rule or regulation applicable to the Company or (B) any order, writ,
judgment, injunction, decree, determination or award which has been entered
against the Company and of which we are aware, the violation or contravention of
which would have a material adverse effect on the Company's business, financial
condition and results of operations.

6. To our knowledge, there is no action, proceeding or investigation pending or
threatened in writing against the Company before any court or administrative
agency that questions the validity of the Merger Agreement.

7. All consents, approvals, authorizations, or orders of, and filings,
registrations, and qualifications with any regulatory authority or governmental
body in the United States required to be obtained by the Company prior to the
Closing in connection with the Company's execution, delivery and performance of
the Merger Agreement and the consummation by the Company of the Merger as
contemplated therein have been made or obtained, other than the filing of the
Agreement of Merger with the Secretary of State of the State of California as
contemplated by Section 1.2 of the Merger Agreement.

8. Assuming due approval by the Board of Directors of Celgene and Merger Sub,
respectively, and the shareholders of the Merger Sub, and compliance by Celgene
and Merger Sub with all requirements of applicable law and the Merger agreement
necessary to effect the Merger, upon the filing of the Agreement of Merger with,
and acceptance of the Agreement of Merger by, the Secretary of State of the
State of California, the Merger will be effective.


                                       D-3
<PAGE>

This opinion is intended solely for your benefit and is not to be made available
to or be relied upon by any other person, firm or entity without prior written
consent.

Sincerely,


COOLEY GODWARD LLP

                                       D-4
<PAGE>
                                                                       EXHIBIT E
     , 2000


Celgene Corporation
7 Powder Horn Drive
Warren, NJ 07059

Ladies and Gentlemen:

This opinion is being delivered to you in connection with Section of the
Agreement and Plan of Merger dated as of June , 2000, (the "Reorganization
Agreement") by and among Celgene Corporation, a Delaware corporation ("Parent"),
Celgene Acquisition Corp., a California corporation and wholly owned subsidiary
of Parent ("Merger Sub"), and Signal Pharmaceuticals, Inc., a California
corporation (the "Company").

Except as otherwise provided, capitalized terms used but not defined herein
shall have the meanings set forth in the Reorganization Agreement. All section
references, unless otherwise indicated, are to the Internal Revenue Code of
1986, as amended (the "Code").

We have acted as counsel to the Parent in connection with the Merger. As such,
and for the purpose of rendering this opinion, we have examined, and are relying
upon (without any independent investigation or review thereof) the truth and
accuracy, at all relevant times, of the statements, covenants, representations
and warranties contained in the following documents (including all exhibits and
schedules attached thereto):

     (A) the Reorganization Agreement;

     (B) the Registration Statement;

     (C) those certain tax representation letters dated , 2000, and delivered to
us by Parent, Merger Sub and the Company (the "Tax Representation Letters"); and

     (D) such other instruments and documents related to the formation,
organization and operation of Parent, Merger Sub and the Company and to the
consummation of the Merger and the other transactions contemplated by the
Reorganization Agreement as we have deemed necessary or appropriate.

In connection with rendering this opinion, we have assumed (without any
independent investigation or review thereof) that:

     (A) Original documents submitted to us (including signatures thereto) are
authentic, documents submitted to us as copies conform to the original
documents, and that all such documents Celgene Corporation , 2000 have been (or
will be by the Effective Time) duly and validly executed and delivered where due
execution and delivery are a prerequisite to the effectiveness thereof;

     (B) All representations, warranties and statements made or agreed to by
Parent, Merger Sub and the Company, their managements, employees, officers,
directors and stockholders in connection with the Merger, including, but not
limited to, those set forth in the Reorganization Agreement (including the
exhibits thereto) and the Tax Representation Letters are true and accurate at
all relevant times;

     (C) All covenants contained in the Reorganization Agreement (including
exhibits thereto) and the Tax Representation Letters are performed without
waiver or breach of any material provision thereof;

     (D) The Merger will be reported by Parent and the Company on their
respective federal income tax returns in a manner consistent with the opinion
set forth below;

     (E) The Merger will be consummated in accordance with the Reorganization
Agreement without any waiver or breach of any material provision thereof, and
the Merger will be effective under applicable state law;

<PAGE>

Celgene Corporation
     , 2000
Page 2


     (F) Any representation or statement made "to the knowledge of" or similarly
qualified is correct without such qualification; and

     (G) The opinion dated , 2000, rendered by Cooley Godward LLP to the Company
pursuant to the Reorganization Agreement has been delivered and has not been
withdrawn.

Based on our examination of the foregoing items and subject to the limitations,
qualifications, assumptions and caveats set forth herein, we are of the opinion
that, for federal income tax purposes, the Merger will be a reorganization
within the meaning of Section 368(a) of the Code.

This opinion does not address the various state, local or foreign tax
consequences that may result from the Merger or the other transactions
contemplated by the Reorganization Agreement. In addition, no opinion is
expressed as to any federal income tax consequence of the Merger or the other
transactions contemplated by the Reorganization Agreement except as specifically
set forth herein, and this opinion may not be relied upon except with respect to
the consequences specifically discussed herein. No opinion is expressed as to
the federal income tax treatment that may be relevant to a particular investor
in light of personal circumstances or to certain types of investors subject to
special treatment under the federal income tax laws (for example, financial
institutions, insurance companies, foreign individuals and entities, tax-exempt
entities, dealers in securities, persons who are subject to the alternative
minimum tax provisions of the Code, persons who acquired their shares of Company
capital stock pursuant to the exercise of an employee option (or otherwise as
compensation), persons whose shares of Company capital stock are qualified small
business stock for purposes of Section 1202 of the Code, or persons who acquired
Company capital stock as part of an integrated investment, such as a "hedge,"
"straddle," or other risk reduction transaction, composed of Company capital
stock and one or more other positions).

No opinion is expressed as to any transaction other than the Merger as described
in the Reorganization Agreement, or as to any transaction whatsoever, including
the Merger, if any of the representations, warranties, statements and
assumptions material to our opinion and upon which we have relied are not
accurate and complete in all material respects at all relevant times.

This opinion only represents our best judgment as to the federal income tax
consequences of the Merger and is not binding on the Internal Revenue Service or
any court of law, tribunal, administrative agency or other governmental body.
The conclusions are based on the Code, existing judicial decisions,
administrative regulations and published rulings. No assurance can be given that
future legislative, judicial or administrative changes or interpretations would
not adversely affect the accuracy of the conclusions stated herein.
Nevertheless, by rendering this opinion, we undertake no responsibility to
advise you of any new developments in the application or interpretation of the
federal income tax laws.

This opinion is being delivered solely in connection with Section of the
Reorganization Agreement. It is intended for the benefit of Parent and may not
be relied upon or utilized for any other purpose or by any other person and may
not be made available to any other person without our prior written consent.

Sincerely,


PROSKAUER ROSE LLP

                                       E-2
<PAGE>

                                  EXHIBIT F TO THE AGREEMENT AND PLAN OF MERGER


                                              , 2000

Signal Pharmaceuticals, Inc.



     Re: Celgene Corporation and Celgene Acquisition Corp.
         -------------------------------------------------

Ladies and Gentlemen:

We have acted as special counsel to Celgene Corporation, a Delaware corporation
(the "Parent"), and Celgene Acquisition Corp., a California corporation (the
"Sub"), in connection with the preparation, authorization, execution and
delivery of, and the consummation of the transactions contemplated by, the
Agreement and Plan of Merger, dated as of June , 2000 (the "Merger Agreement"),
among Parent, Sub and Signal Pharmaceuticals, Inc., a California corporation
(the "Company"). This opinion is being delivered to you pursuant to Section
8.3(c) of the Merger Agreement. Capitalized terms used and not otherwise defined
herein shall have the meanings ascribed to them in the Merger Agreement.

We have examined the Merger Agreement, Registration Statement and such
certificates of public officials, such certificates of officers of Parent and
Sub, the originals (or copies thereof) of such corporate documents and records
of Parent and Sub, and such other documents and instruments as we have deemed
necessary or appropriate for purposes of this opinion. In this connection, we
have assumed the legal capacity of natural persons, the genuineness of
signatures on, and the authenticity of, all documents so examined, the
conformity to originals of all documents submitted to us as copies, and that all
corporate records or other information made available to us by the Parent and
Sub, and on which we have relied, are complete in all respects. As to the
accuracy of matters of fact, we have relied solely upon the above-mentioned
certificates and upon the representations contained in the Merger Agreement and
other documents delivered pursuant thereto and have assumed that certificates of
public officials dated prior to the date hereof remain accurate as of the date
hereof.

Based on the foregoing, we are of the opinion that:

      i.  Parent is a corporation validly existing and in good standing under
          the laws of the State of Delaware. Sub is a corporation duly formed,
          validly existing and in good standing under the laws of the State of
          California.

      ii. The authorized capital stock of Parent consists of 120,000,000 shares
          of Parent Common Stock and 5,000,000 shares of Parent Preferred Stock.
          All of the shares of Parent Common Stock to be issued upon
          consummation of the Merger (the "Merger Shares") are duly authorized
          and, when issued in accordance with the Agreement, will be validly
          issued, fully paid and nonassessable.

     iii. The authorized capital stock of Sub consists of shares of Sub Common
          Stock, of which shares, as of the date hereof, are issued and
          outstanding. All of such outstanding shares are owned of record and,
          to our knowledge, beneficially by Parent, and are validly issued,
          fully paid and nonassessable.

      iv. The Parent has all requisite corporate power and authority to own,
          lease and operate its properties and to carry on its business as now
          being conducted.

      v.  The issuance of the Merger Shares in accordance with the Merger
          Agreement has been registered under the Securities Act of 1933, as
          amended, and is either registered or exempt from registration under
          all applicable state securities or blue sky laws.
<PAGE>

Signal Pharmaceuticals, Inc.
    , 2000
Page 2

      vi. Each of Parent and Sub has all necessary corporate power and authority
          to execute and deliver the Agreement, to perform its obligations
          thereunder, and to consummate the transactions contemplated thereby.
          The execution, delivery and performance of the Agreement and the
          consummation by Parent and Sub of the transactions contemplated
          thereby have been authorized by all necessary corporate action on the
          part of each of Parent and Sub. Upon the filing of the Agreement of
          Merger with the Department of State of California, all steps required
          to be taken by Parent and Sub under the laws of the State of
          California to effect the Merger of Sub with and into the Company shall
          have been duly and properly taken.

     vii. The Agreement has been duly executed and delivered by each of Parent
          and Sub and constitutes the valid and binding obligation of each of
          Parent and Sub enforceable in accordance with its terms, except to the
          extent that enforceability may be subject to applicable bankruptcy,
          insolvency, fraudulent conveyance, fraudulent transfer,
          reorganization, moratorium and similar laws presently or hereafter in
          effect affecting the enforcement of creditors' rights generally and by
          general equitable principles (regardless of whether enforcement is
          sought in a proceeding in law or in equity).

    viii. The execution, delivery and performance of the Agreement by each of
          Parent and Sub and the consummation by each of Parent and Sub of the
          transactions contemplated thereby will not result in a violation of
          any provision of their respective certificates of incorporation (as
          amended, in the case of Parent) or by-laws.

      ix. Except for the filing of the Agreement of Merger in California, we
          have no knowledge of any consent or approval which is required in
          connection with the consummation by Parent and Sub of the transactions
          contemplated by the Agreement which have not been obtained.

      x.  We have no knowledge of any action, suit, proceeding or investigation
          which is pending or threatened which questions the validity of the
          Agreement or any action taken or to be taken by Parent or Sub in
          connection with the Agreement.

We have participated in the preparation of the Registration Statement and
meetings with members of management of Parent and its independent certified
public accountants relating to the disclosure contained in the Registration
Statement as it pertains to Parent or Sub. Although we are not passing upon and
do not assume any responsibility for the accuracy, completeness or fullness of
the information relating to Parent or Sub contained in the Registration
Statement, nothing has come to our attention that has caused us to believe that
at the date such materials were mailed to the shareholders of the Company,
and/or filed with the Commission, as applicable, and at the Closing Date, the
information relating to Parent or Sub in the Registration Statement contained
any misstatement of a material fact or omission of a material fact necessary to
make the statements therein, in light of the circumstances under which they were
made, not misleading (except that no statement is made with respect to any
financial statements or schedules, or other financial or statistical data
contained therein).

The foregoing opinions are subject to the following qualifications:

      a.  No opinion is expressed as to the enforceability of any choice of law,
          jurisdiction, venue or service of process provisions of any document.

      b.  Limitations imposed by state law, federal law or general equitable
          principles upon the specified enforceability of any of the remedies,
          covenants or other provisions of any applicable agreement and upon the
          availability of injunctive relief or other equitable remedies,
          regardless of whether enforcement of any such agreement is considered
          in a proceeding in equity or at law.


                                       F-2
<PAGE>

Signal Pharmaceuticals, Inc.
    , 2000
Page 3

      c.  The unenforceability under certain circumstances of provisions
          indemnifying a party against, or requiring contributions toward, that
          party's liability for its own wrongful or negligent acts, or where
          indemnification or contribution may be limited by state or federal
          securities laws or is contrary to public policy.

We have further assumed with your permission, without any inquiry, investigation
or verification, the following matters:

      i.  That the factual matters (including representations and warranties)
          contained in the Merger Agreement are true and correct as set forth
          therein; and

      ii. That any certificate, representation or document upon which we have
          relied and which was given or dated earlier than the date of this
          letter continues to remain accurate, insofar as relevant to the
          opinions contained herein, from such earlier date through and
          including the date hereof.

Our opinions hereunder are based solely upon the laws, rulings, administrative
interpretations and regulations in effect on the date hereof and are subject to
modification to the extent that such laws, rulings, interpretations and
regulations are changed in the future. By delivery of this letter, we have
assumed no obligation to update our opinions for changes in such laws, rulings,
interpretations and regulations or for events occurring subsequent to the date
hereof.

This opinion is limited to the matters  stated  herein and no opinion is implied
or may be inferred beyond the matters expressly stated herein.

The opinions expressed herein relate solely to the Delaware General Corporation
Law, the laws of the State of California and the federal laws of the United
States of America, and no opinion is expressed with respect to the laws of any
other jurisdiction.

Any references in this opinion to matters to our "knowledge" or words of similar
import refer only to the actual present knowledge of attorneys at our firm who
have been actively involved in this transaction, after due inquiry of those
attorneys. Except as otherwise stated herein, we have undertaken no independent
investigation or verification of factual matters.

This opinion is solely for the information of the addressees hereof and is not
to be quoted in whole or in part or otherwise referred to (except in a list of
closing documents), nor is it to be filed with any governmental agency or other
person without our prior written consent. Other than the addressees hereof, no
one is entitled to rely on this opinion without our prior written consent.

                                        Very truly yours,

                                       F-3
<PAGE>

                                                                       EXHIBIT G

______, 2000


Signal Pharmaceuticals, Inc.

-----------------------

-----------------------

Ladies and Gentlemen:

This opinion is being delivered to you in connection with Section 8.3(d) of the
Agreement and Plan of Merger dated as of June , 2000 (the "Reorganization
Agreement") by and among Celgene Corporation, a Delaware corporation ("Parent"),
Celgene Acquisition Corp., a California corporation and wholly owned subsidiary
of Parent ("Merger Sub"), and Signal Pharmaceuticals, Inc., a California
corporation (the "Company").

Except as otherwise provided, capitalized terms used but not defined herein
shall have the meanings set forth in the Reorganization Agreement. All section
references, unless otherwise indicated, are to the Internal Revenue Code of
1986, as amended (the "Code").

We have acted as counsel to the Company in connection with the Merger. As such,
and for the purpose of rendering this opinion, we have examined, and are relying
upon (without any independent investigation or review thereof) the truth and
accuracy, at all relevant times, of the statements, covenants, representations
and warranties contained in the following documents (including all exhibits and
schedules attached thereto):

     (a) the Reorganization Agreement;

     (b) the Registration Statement;

     (c) those certain tax representation letters dated , 2000, and delivered to
us by Parent, Merger Sub and the Company (the "Tax Representation Letters"); and

     (d) such other instruments and documents related to the formation,
organization and operation of Parent, Merger Sub and the Company and to the
consummation of the Merger and the other transactions contemplated by the
Reorganization Agreement as we have deemed necessary or appropriate.

In connection with rendering this opinion, we have assumed (without any
independent investigation or review thereof) that:

     (a) Original documents submitted to us (including signatures thereto) are
authentic, documents submitted to us as copies conform to the original
documents, and that all such documents have been

<PAGE>

Signal Pharmaceuticals, Inc.
_____________,2000
Page Two

(or will be by the Effective Time) duly and validly executed and delivered where
due execution and delivery are a prerequisite to the effectiveness thereof;

     (b) All representations, warranties and statements made or agreed to by
Parent, Merger Sub and the Company, their managements, employees, officers,
directors and stockholders in connection with the Merger, including, but not
limited to, those set forth in the Reorganization Agreement (including the
exhibits thereto) and the Tax Representation Letters are true and accurate at
all relevant times;

     (c) All covenants contained in the Reorganization Agreement (including
exhibits thereto) and the Tax Representation Letters are performed without
waiver or breach of any material provision thereof;

     (d) The merger will be reported by Parent and the Company on their
respective federal income tax returns in a manner consistent with the opinion
set forth below;

     (e) The Merger will be consummated in accordance with the Reorganization
Agreement without any waiver or breach of any material provision thereof, and
the Merger will be effective under applicable state law;

     (f) Any representation or statement made "to the knowledge of" or similarly
qualified is correct without such qualification; and

     (g) The opinion dated ________,2000, rendered by Proskauer Rose LLP to
Parent pursuant to the Reorganization Agreement has been delivered and has not
been withdrawn.

Based on our examination of the foregoing items and subject to the limitations,
qualifications, assumptions and caveats set forth herein, we are of the opinion
that, for federal income tax purposes, the Merger will be a reorganization
within the meaning of Section 368(a) of the Code.

This opinion does not address the various state, local or foreign tax
consequences that may result from the Merger or the other transactions
contemplated by the Reorganization Agreement. In addition, no opinion is
expressed as to any federal income tax consequence of the Merger of the other
transactions contemplated by the Reorganization Agreement except as specifically
set forth herein, and this opinion may not be relied upon except with respect to
the consequences specifically discussed herein. No opinion is expressed as to
the federal income tax treatment that may be relevant to a particular investor
in light of personal circumstances or to certain types of investors subject to
special treatment under the federal income tax laws (for example, financial
institutions, insurance companies, foreign individuals and entities, tax-exempt
entities, dealers in securities, persons who are



                                       G-2
<PAGE>

Signal Pharmaceuticals, Inc.
_____________,2000
Page Three

subject to the alternative minimum tax provisions of the Code, persons who
acquired their shares of Company capital stock pursuant to the exercise of an
employee option (or otherwise as compensation), persons whose shares of Company
capital stock are qualified small business stock for purposes of Section 1202 of
the Code, or persons who acquired Company capital stock as part of an integrated
investment, such as a "hedge," "straddle," or other risk reduction transaction,
composed of Company capital stock and one or more other positions).

No opinion is expressed as to any transaction other than the Merger as described
in the Reorganization Agreement, or as to any transaction whatsoever, including
the Merger, if any of the representations, warranties, statements and
assumptions material to our opinion and upon which we have relied are not
accurate and complete in all material respects at all relevant times.

This opinion only represents our best judgment as to the federal income tax
consequences of the Merger and is not binding on the Internal Revenue Service or
any court of law, tribunal, administrative agency or other governmental body.
The conclusions are based on the Code, existing judicial decisions,
administrative regulations and published rulings. No assurance can be given that
future legislative, judicial or administrative changes or interpretations would
not adversely affect the accuracy of the conclusions stated herein.
Nevertheless, by rendering this opinion, we undertake no responsibility to
advise you of any new developments in the application or interpretation of the
federal income tax laws.

This opinion is being delivered solely in connection with Section 8.3(d) of the
Reorganization Agreement. It is intended for the benefit of the Company and may
not be relied upon or utilized for any other purpose or by any other person and
may not be made available to any other person without our prior written consent.

Sincerely,



COOLEY GODWARD LLP

                                       G-3
<PAGE>

                                   APPENDIX B
                       CALIFORNIA GENERAL CORPORATION LAW


CHAPTER 13. DISSENTERS' RIGHTS


1300. RIGHT TO REQUIRE PURCHASE - "DISSENTING SHARES" AND "DISSENTING
SHAREHOLDER" DEFINED. - (a) If the approval of the outstanding shares (Section
152) of a corporation is required for a reorganization under subdivisions (a)
and (b) or subdivision (e) or (f) of Section 1201, each shareholder of the
corporation entitled to vote on the transaction and each shareholder of a
subsidiary corporation in a short-form merger may, by complying with this
chapter, require the corporation in which the shareholder holds shares to
purchase for cash at their fair market value the shares owned by the shareholder
which are dissenting shares as defined in subdivision (b). The fair market value
shall be determined as of the day before the first announcement of the terms of
the proposed reorganization or short-form merger, excluding any appreciation or
depreciation in consequence of the proposed action, but adjusted for any stock
split, reverse stock split, or share dividend which becomes effective
thereafter.


(b) As used in this chapter, "dissenting shares" means shares which come within
all of the following descriptions:


(1) Which were not immediately prior to the reorganization or short-form merger
either (A) listed on any national securities exchange certified by the
Commissioner of Corporations; under subdivision (o) of Section 25100 or (B)
listed on the National Market System of the NASDAQ Stock Market, and the notice
of meeting of shareholders to act upon the reorganization summarizes this
section and Sections 1301, 1302, 1303 and 1304; provided, however, that this
provision does not apply to any shares with respect to which there exists any
restriction on transfer imposed by the corporation or by any law or regulation;
and provided, further, that this provision does not apply to any class of shares
described in subparagraph (A) or (B) if demands for payment are filed with
respect to 5 percent or more of the outstanding shares of that class.


(2) Which were outstanding on the date for the determination of shareholders
entitled to vote on the reorganization and (A) were not voted in favor of the
reorganization or, (B) if described in subparagraph (A) or (B) of paragraph (1)
(without regard to the provisos in that paragraph), were voted against the
reorganization, or which were held of record on the effective date of a
short-form merger; provided, however, that subparagraph (A) rather than
subparagraph (B) of this paragraph applies in any case where the approval
required by Section 1201 is sought by written consent rather than at a meeting.



(3) Which the dissenting shareholder has demanded that the corporation purchase
at their fair market value, in accordance with Section 1301.


(4) Which the dissenting shareholder has submitted for endorsement, in
accordance with Section 1302.


(c) As used in this chapter, "dissenting shareholder" means the recordholder of
dissenting shares and includes a transferee of record.


1301. DEMAND FOR PURCHASE. (a) If, in the case of a reorganization, any
shareholders of a corporation have a right under Section 1300, subject to
compliance with paragraphs (3) and (4) of subdivision (b) thereof, to require
the corporation to purchase their shares for cash, such corporation shall mail
to each such shareholder a notice of the approval of the reorganization by its
outstanding shares (Section 152) within 10 days after the date of such approval,
accompanied by a copy of Sections 1300, 1302, 1303, 1304 and this section, a
statement of the price determined by the corporation to represent the fair
market value of the dissenting shares, and a brief description of the procedure
to be followed if the shareholder desires to exercise the shareholder's right
under such sections. The statement of price constitutes an offer by the
corporation to purchase at the price stated any dissenting shares as defined in
subdivision (b) of Section 1300, unless they lose their status as dissenting
shares under Section 1309.
<PAGE>

(b) Any shareholder who has a right to require the corporation to purchase the
shareholder's shares for cash under Section 1300, subject to compliance with
paragraphs (3) and (4) of subdivision (b) thereof, and who desires the
corporation to purchase such shares shall make written demand upon the
corporation for the purchase of such shares and payment to the shareholder in
cash of their fair market value. The demand is not effective for any purpose
unless it is received by the corporation or any transfer agent thereof (1) in
the case of shares described in clause (i) or (ii) of paragraph (1) of
subdivision (b) of Section 1300 (without regard to the provisos in that
paragraph), not later than the date of the shareholders' meeting to vote upon
the reorganization, or (2) in any other case within 30 days after the date on
which the notice of the approval by the outstanding shares pursuant to
subdivision (a) or the notice pursuant to subdivision (i) of Section 1110 was
mailed to the shareholder.

(c) The demand shall state the number and class of the shares held of record by
the shareholder which the shareholder demands that the corporation purchase and
shall contain a statement of what such shareholder claims to be the fair market
value of those shares as of the day before the announcement of the proposed
reorganization or short-form merger. The statement of fair market value
constitutes an offer by the shareholder to sell the shares at such price.

1302. ENDORSEMENT OF SHARES. - Within 30 days after the date on which notice of
the approval by the outstanding shares or the notice pursuant to subdivision (i)
of Section 1110 was mailed to the shareholder, the shareholder shall submit to
the corporation at its principal office or at the office of any transfer agent
thereof, (a) if the shares are certificated securities, the shareholder's
certificates representing any shares which the shareholder demands that the
corporation purchase, to be stamped or endorsed with a statement that the shares
are dissenting shares or to be exchanged for certificates of appropriate
denomination so stamped or endorsed or (b) if the shares are uncertificated
securities, written notice of the number of shares which the shareholder demands
that the corporation purchase. Upon subsequent transfers of the dissenting
shares on the books of the corporation, the new certificates, initial
transaction statement, and other written statements issued therefor shall bear a
like statement, together with the name of the original dissenting holder of the
shares.

1303. AGREED PRICE - TIME FOR PAYMENT. - (a) If the corporation and the
shareholder agree that the shares are dissenting shares and agree upon the price
of the shares, the dissenting shareholder is entitled to the agreed price with
interest thereon at the legal rate on judgments from the date of the agreement.
Any agreements fixing the fair market value of any dissenting shares as between
the corporation and the holders thereof shall be filed with the secretary of the
corporation.

(b) Subject to the provisions of Section 1306, payment of the fair market value
of dissenting shares shall be made within 30 days after the amount thereof has
been agreed or within 30 days after any statutory or contractual conditions to
the reorganization are satisfied, whichever is later, and in the case of
certificated securities, subject to surrender of the certificates therefor,
unless provided otherwise by agreement.

1304. DISSENTERS' ACTION TO ENFORCE PAYMENT. - (a) If the corporation denies
that the shares are dissenting shares, or the corporation and the shareholder
fail to agree upon the fair market value of the shares, then the shareholder
demanding purchase of such shares as dissenting shares or any interested
corporation, within six months after the date on which notice of the approval by
the outstanding shares (Section 152) or notice pursuant to subdivision (i) of
Section 1110 was mailed to the shareholder, but not thereafter, may file a
complaint in the superior court of the proper county praying the court to
determine whether the shares are dissenting shares or the fair market value of
the dissenting shares or both or may intervene in any action pending on such a
complaint.

(b) Two or more dissenting shareholders may join as plaintiffs or be joined as
defendants in any such action and two or more such actions may be consolidated.


(c) On the trial of the action, the court shall determine the issues. If the
status of the shares as dissenting shares is in issue, the court shall first
determine that issue. If the fair market value of the dissenting shares is in
issue, the court shall determine, or shall appoint one or more impartial
appraisers to determine, the fair market value of the shares.


                                       B-2
<PAGE>

1305. APPRAISERS' REPORT - PAYMENT - COSTS. - (a) If the court appoints an
appraiser or appraisers, they shall proceed forthwith to determine the fair
market value per share. Within the time fixed by the court, the appraisers, or a
majority of them, shall make and file a report in the office of the clerk of the
court. Thereupon, on the motion of any party, the report shall be submitted to
the court and considered on such evidence as the court considers relevant. If
the court finds the report reasonable, the court may confirm it.


(b) If a majority of the appraisers appointed fail to make and file a report
within 10 days from the date of their appointment or within such further time as
may be allowed by the court or the report is not confirmed by the court, the
court shall determine the fair market value of the dissenting shares.


(c) Subject to the provisions of Section 1306, judgment shall be rendered
against the corporation for payment of an amount equal to the fair market value
of each dissenting share multiplied by the number of dissenting shares which any
dissenting shareholder who is a party, or who has intervened, is entitled to
require the corporation to purchase, with interest thereon at the legal rate
from the date on which judgment was entered.


(d) Any such judgment shall be payable forthwith with respect to uncertificated
securities and, with respect to certificated securities, only upon the
endorsement and delivery to the corporation of the certificates for the shares
described in the judgment. Any party may appeal from the judgment.


(e) The costs of the action, including reasonable compensation to the appraisers
to be fixed by the court, shall be assessed or apportioned as the court
considers equitable, but, if the appraisal exceeds the price offered by the
corporation, the corporation shall pay the costs (including in the discretion of
the court attorneys' fees, fees of expert witnesses and interest at the legal
rate on judgments from the date of compliance with Sections 1300, 1301 and 1302
if the value awarded by the court for the shares is more than 125 percent of the
price offered by the corporation under subdivision (a) of Section 1301).


1306. DISSENTING SHAREHOLDER'S STATUS AS CREDITOR. - To the extent that the
provisions of Chapter 5 prevent the payment to any holders of dissenting shares
of their fair market value, they shall become creditors of the corporation for
the amount thereof together with interest at the legal rate on judgments until
the date of payment, but subordinate to all other creditors in any liquidation
proceeding, such debt to be payable when permissible under the provisions of
Chapter 5.


1307. DIVIDENDS PAID AS CREDIT AGAINST PAYMENT. - Cash dividends declared and
paid by the corporation upon the dissenting shares after the date of approval of
the reorganization by the outstanding shares (Section 152) and prior to payment
for the shares by the corporation shall be credited against the total amount to
be paid by the corporation therefor.


1308. CONTINUING RIGHTS AND PRIVILEGES OF DISSENTING SHAREHOLDERS. - Except as
expressly limited in this chapter, holders of dissenting shares continue to have
all the rights and privileges incident to their shares, until the fair market
value of their shares is agreed upon or determined. A dissenting shareholder may
not withdraw a demand for payment unless the corporation consents thereto.


1309. TERMINATION OF DISSENTING SHAREHOLDER STATUS. - Dissenting shares lose
their status as dissenting shares and the holders thereof cease to be dissenting
shareholders and cease to be entitled to require the corporation to purchase
their shares upon the happening of any of the following:


(a) The corporation abandons the reorganization. Upon abandonment of the
reorganization, the corporation shall pay on demand to any dissenting
shareholder who has initiated proceedings in good faith under this chapter all
necessary expenses incurred in such proceedings and reasonable attorneys' fees.



(b) The shares are transferred prior to their submission for endorsement in
accordance with Section 1302 or are surrendered for conversion into shares of
another class in accordance with the articles.


                                       B-3
<PAGE>

(c) The dissenting shareholder and the corporation do not agree upon the status
of the shares as dissenting shares or upon the purchase price of the shares, and
neither files a complaint or intervenes in a pending action as provided in
Section 1304, within six months after the date on which notice of the approval
by the outstanding shares or notice pursuant to subdivision (i) of Section 1110
was mailed to the shareholder.

(d) The dissenting shareholder, with the consent of the corporation, withdraws
the shareholder's demand for purchase of the dissenting shares.

1310. SUSPENSION OF PROCEEDINGS FOR PAYMENT PENDING LITIGATION. - If litigation
is instituted to test the sufficiency or regularity of the votes of the
shareholders in authorizing a reorganization, any proceedings under Section 1304
and 1305 shall be suspended until final determination of such litigation.

1311. EXEMPT SHARES. - This chapter, except Section 1312, does not apply to
classes of shares whose terms and provisions specifically set forth the amount
to be paid in respect to such shares in the event of a reorganization or merger.

1312. ATTACKING VALIDITY OF REORGANIZATION OR MERGER. - (a) No shareholder of a
corporation who has a right under this chapter to demand payment of cash for the
shares held by the shareholder shall have any right at law or in equity to
attack the validity of the reorganization or short-form merger, or to have the
reorganization or short-form merger set aside or rescinded, except in an action
to test whether the number of shares required to authorize or approve the
reorganization have been legally voted in favor thereof; but any holder of
shares of a class whose terms and provisions specifically set forth the amount
to be paid in respect to them in the event of a reorganization or short-form
merger is entitled to payment in accordance with those terms and provisions or,
if the principal terms of the reorganization are approved pursuant to
subdivision (b) of Section 1202, is entitled to payment in accordance with the
terms and provisions of the approved reorganization.

(b) If one of the parties to a reorganization or short-form merger is directly
or indirectly controlled, by, or under common control with, another party to the
reorganization or short-form merger, subdivision (a) shall not apply to any
shareholder of such party who has not demanded payment of cash for such
shareholder's shares pursuant to this chapter; but if the shareholder institutes
any action to attack the validity of the reorganization or short-form merger or
to have the reorganization or short-form merger set aside or rescinded, the
shareholder shall not thereafter have any right to demand payment of cash for
the shareholder's shares pursuant to this chapter. The court in any action
attacking the validity of the reorganization or short-form merger or to have the
reorganization or short-form merger set aside or rescinded shall not restrain or
enjoin the consummation of the transaction except upon 10 days' prior notice to
the corporation and upon a determination by the court that clearly no other
remedy will adequately protect the complaining shareholder or the class of
shareholders of which such shareholder is a member.

(c) If one of the parties to a reorganization or short-form merger is directly
or indirectly controlled by, or under common control with, another party to the
reorganization or short-form merger, in any action to attack the validity of the
reorganization or short-form merger or to have the reorganization or short-form
merger set aside or rescinded, (1) a party to a reorganization or short-form
merger which controls another party to the reorganization or short-form merger
shall have the burden of proving that the transaction is just and reasonable as
to the shareholders of the controlled party, and (2) a person who controls two
or more parties to a reorganization shall have the burden of proving that the
transaction is just and reasonable as to the shareholders of any party so
controlled.


                                       B-4
<PAGE>

                                   APPENDIX C


[GRAPHIC OMITTED]


                                        June 28, 2000

Board of Directors
Signal Pharmaceuticals, Inc.
5555 Oberlin Drive
San Diego, CA 92121

Members of the Board:

We understand that Signal Pharmaceuticals, Inc. ("Company"), Celgene Corporation
("Acquiror"), and Celgene Acquisition Corp. (a wholly owned subsidiary of
Acquiror, "Merger Sub") are proposing to enter into an Agreement and Plan of
Merger (the "Agreement") which will provide, among other things, for the merger
(the "Merger") of Merger Sub with and into the Company. Upon consummation of the
Merger, the Company will become a wholly owned subsidiary of Acquiror.

Under the terms, and subject to the conditions, of the Agreement, (i)
immediately prior to the Merger, all outstanding shares of preferred stock of
the Company (collectively, "Company Preferred Stock") will be converted into
shares of common stock of the Company, par value $0.001 per share ("Company
Common Stock") and (ii) at effective time of the Merger, each outstanding share
of Company Common Stock, other than certain shares to be canceled pursuant to
the Agreement and shares held by stockholders who properly exercise dissenters'
rights ("Dissenting Shares"), will be converted into the right to receive 0.1257
shares (the "Exchange Ratio") of the common stock of Acquiror, par value $0.01
per share ("Acquiror Common Stock"). In connection with the Agreement, (i)
certain holders of shares of Company Common Stock and Company Preferred Stock
will enter into Voting and Proxy Agreements with Acquiror (the "Voting
Agreements") and (ii) the Company and Acquiror will enter into a stock option
agreement (the "Option Agreement") granting Acquiror an option to purchase
shares of Company Common Stock in certain circumstances. The terms and
conditions of the Merger are set out more fully in the Agreement.

You have asked us whether, in our opinion, the Exchange Ratio is fair from a
financial point of view and as of the date hereof to the "Holders of Company
Common Stock." The "Holders of Company Common Stock" shall be defined as all
holders of Company Common Stock (including holders of Company Preferred Stock
which is to be converted into Company Common Stock immediately prior to the
Merger) other than Acquiror, Merger Sub, any affiliates of Acquiror or Merger
Sub or holders of Dissenting Shares; provided that with respect to any holders
of Company Common Stock who are officers or directors (or who have
representatives serving as directors) of the Company, we have expressed our
opinion as to such holders solely in their capacity as holders of Company Common
Stock and have not taken into account any other agreements or arrangements that
they may have in connection with the Merger. For the purposes of this opinion we
have, among other things:

   (i)  reviewed certain publicly available financial statements and other
        business and financial information of the Company and Acquiror,
        respectively;

   (ii) reviewed certain internal financial statements and other financial and
        operating data, including certain financial forecasts and other forward
        looking information, concerning the Company prepared by the management
        of the Company;

   (iii) reviewed certain publicly available estimates of research analysts
        relating to Acquiror;
<PAGE>

Board of Directors
Signal Pharmaceuticals, Inc.
June 28, 2000
Page 2

   (iv)  held discussions with the respective managements of the Company and
         Acquiror concerning the businesses, past and current operations,
         financial condition and future prospects of both the Company and
         Acquiror, independently and combined, including discussions with the
         managements of the Company and Acquiror concerning cost savings and
         other synergies that are expected to result from the Merger as well as
         their views regarding the strategic rationale for the Merger;

   (v)   reviewed the financial terms and conditions set forth in drafts, dated
         June 26, 2000, of the Agreement, Voting Agreements and Option Agreement
         (collectively, the "Draft Agreements");

   (vi)  reviewed the stock price and trading history of Acquiror Common Stock;

   (vii) compared the financial performance of Acquiror and the prices and
         trading activity of Acquiror Common Stock with that of certain other
         publicly traded companies comparable with Acquiror;

   (viii) compared the financial performance of the Company with that of certain
        publicly traded companies comparable to the Company;

   (ix) compared the financial terms of the Merger with the financial terms, to
        the extent publicly available, of other transactions that we deemed
        relevant;

   (x)  reviewed the pro forma impact of the Merger;

   (xi) participated in discussions and negotiations among representatives of
        the Company and Acquiror and their financial and legal advisors; and

  (xii) made such other studies and inquiries, and reviewed such other data, as
        we deemed relevant.

In our review and analysis, and in arriving at our opinion, we have assumed and
relied upon the accuracy and completeness of all of the financial and other
information provided to us (including information furnished to us orally or
otherwise discussed with us by the managements of the Company and Acquiror) or
publicly available and have neither attempted to verify, nor assumed
responsibility for verifying, any of such information. We have relied upon the
assurances of the managements of the Company and Acquiror that they are not
aware of any facts that would make such information inaccurate or misleading.
Furthermore, we did not obtain or make, or assume any responsibility for
obtaining or making, any independent evaluation or appraisal of the properties,
assets or liabilities (contingent or otherwise) of the Company or Acquiror, nor
were we furnished with any such evaluation or appraisal. With respect to the
financial forecasts and other forward looking financial information (and the
assumptions and bases therefore) for each of the Company and Acquiror that we
have reviewed, we have assumed that such forecasts and other forward looking
financial information have been reasonably prepared in good faith on the basis
of reasonable assumptions and reflect the best currently available estimates and
judgments as to the future financial condition and performance of each of the
Company and Acquiror, respectively, and we have further assumed that such
forecasts, and other forward looking financial information will be realized in
the amounts and in the time periods currently estimated. We have assumed that
the Merger will be consummated upon the terms set forth in the Draft Agreements
without material alteration thereof, including, among other things, that the
Merger will be accounted for as a "pooling-of-interests" business combination in
accordance with U.S. generally accepted accounting principles ("GAAP") and that
the Merger will be treated as a tax-free reorganization pursuant to the Internal
Revenue Code of 1986, as amended. In addition, we have assumed that the
historical financial statements of each of the Company and Acquiror reviewed by
us have been prepared and fairly presented in accordance with U.S. GAAP
consistently applied.


                                       C-2
<PAGE>

Board of Directors
Signal Pharmaceuticals, Inc.
June 28, 2000
Page 3

This opinion is necessarily based upon market, economic and other conditions as
in effect on, and information made available to us as of, the date hereof. It
should be understood that subsequent developments may affect the conclusion
expressed in this opinion and that we disclaim any undertaking or obligation to
advise any person of any change in any fact or matter affecting this opinion
which may come or be brought to our attention after the date of this opinion.
Our opinion is limited to the fairness, from a financial point of view and as to
the date hereof, to the Holders of Company Common Stock of the Exchange Ratio.
We do not express any opinion as to (i) the value of any employee agreement or
other arrangement entered into in connection with the Merger, (ii) any tax or
other consequences that might result from the Merger or (iii) what the value of
Acquiror Common Stock will be when issued to the Company's stockholders pursuant
to the Merger or the price at which the shares of Acquiror Common Stock that are
issued pursuant to the Merger may be traded in the future. Our opinion does not
address the relative merits of the Merger and the other business strategies that
the Company's Board of Directors has considered or may be considering, nor does
it address the decision of the Company's Board of Directors to proceed with the
Merger.

In connection with the preparation of our opinion, we were not authorized to
solicit, and did not solicit, third parties regarding alternatives to the
Merger.

We are acting as financial advisor to the Company in connection with the Merger
and will receive (i) a fee contingent upon the delivery of this opinion
irrespective of the conclusion reached herein and (ii) an additional fee
contingent upon the consummation of the Merger. In addition, the Company has
agreed to indemnify us for certain liabilities that may arise out of our
engagement. In the past, we have provided certain investment banking services to
the Company including acting as lead manager for the Company's filing of an
initial public offering, and we and our affiliates are also shareholders of the
Company. In the ordinary course of business, we may trade in Acquiror's
securities for our own account and the account of our customers and,
accordingly, may at any time hold a long or short position in Acquiror's
securities.

Our opinion expressed herein is provided for the information of the Board of
Directors of the Company in connection with its evaluation of the Merger. Our
opinion is not intended to be and does not constitute a recommendation to any
stockholder of the Company as to how such stockholder should vote, or take any
other action, with respect to the Merger. This opinion may not be summarized,
described or referred to or furnished to any party except with our express prior
written consent.

Based upon and subject to the foregoing considerations, it is our opinion that,
as of the date hereof, the Exchange Ratio is fair to the Holders of Company
Common Stock from a financial point of view.

                                     Very truly yours,


                                     /s/ FleetBoston Robertson Stephens Inc.


                                     FLEETBOSTON ROBERTSON STEPHENS INC.

                                       C-3
<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                          INDEX TO FINANCIAL STATEMENTS





                                                              PAGE
                                                             -----
Report of Ernst & Young LLP, Independent Auditors ..........  F-2
Balance Sheets .............................................  F-3
Statements of Operations ...................................  F-4
Statements of Stockholders' Equity .........................  F-5
Statements of Cash Flows ...................................  F-6
Notes to Financial Statements ..............................  F-8



                                       F-1
<PAGE>

               REPORT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS

The Board of Directors
Signal Pharmaceuticals, Inc.


     We have audited the accompanying balance sheets of Signal Pharmaceuticals,
Inc. as of December 31, 1998 and 1999, and the related statements of operations,
stockholders' equity, and cash flows for each of the three years in the period
ended December 31, 1999. These financial statements are the responsibility of
the Company's management. Our responsibility is to express an opinion on these
financial statements based on our audits.

     We conducted our audits in accordance with auditing standards generally
accepted in the United States. Those standards require that we plan and perform
the audit to obtain reasonable assurance about whether the financial statements
are free of material misstatement. An audit includes examining, on a test basis,
evidence supporting the amounts and disclosures in the financial statements. An
audit also includes assessing the accounting principles used and significant
estimates made by management, as well as evaluating the overall financial
statement presentation. We believe that our audits provide a reasonable basis
for our opinion.

     In our opinion, the financial statements referred to above present fairly,
in all material respects, the financial position of Signal Pharmaceuticals, Inc.
at December 31, 1998 and 1999, and the results of its operations and its cash
flows for each of the three years in the period ended December 1999, in
conformity with accounting principles generally accepted in the United States.


                                                    Ernst & Young LLP


San Diego, California
February 4, 2000

                                       F-2
<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                                 BALANCE SHEETS



<TABLE>
<CAPTION>
                                                                        DECEMBER 31,               MARCH 31,
                                                              --------------------------------  ---------------
                                                                    1998             1999             2000
                                                              ---------------  ---------------  ---------------
                                                                                                    (UNAUDITED)
<S>                                                           <C>              <C>              <C>
                          ASSETS
Current assets:
 Cash and cash equivalents .................................   $   6,496,363    $   6,613,834    $   5,815,144
 Short-term investments ....................................       6,456,226        2,806,093          522,226
 Grant revenue receivable ..................................         147,248          108,959           77,425
 Other current assets ......................................         487,234          427,394        1,049,964
                                                               -------------    -------------    -------------
   Total current assets ....................................      13,587,071        9,956,280        7,464,759
Property and equipment, net ................................       4,497,541        3,405,147        3,100,525
Licensed technology, net ...................................         916,668          583,338          499,004
Deposits and other assets ..................................         223,520          202,605          195,430
Notes receivable from officers .............................         333,419          391,495          390,000
                                                               -------------    -------------    -------------
   Total assets ............................................   $  19,558,219    $  14,538,865    $  11,649,718
                                                               =============    =============    =============
            LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
 Accounts payable ..........................................   $     461,967    $     896,260    $     738,488
 Accrued liabilities .......................................         872,484          522,454        1,387,742
 Current portion of promissory note ........................       1,000,080          396,817          158,589
 Current portion of obligations under capital leases
   and equipment notes payable .............................         432,122          730,765          762,542
 Current portion of deferred revenue under
   collaborative agreements ................................       1,697,775        3,449,790        3,524,795
                                                               -------------    -------------    -------------
   Total current liabilities ...............................       4,464,428        5,996,086        6,572,156
Promissory note, net of current portion ....................         349,674               --               --
Obligations under capital leases and equipment notes
 payable, net of current portion ...........................       2,110,651        1,805,297        1,569,610
Deferred revenue under collaborative agreements, net
 of current portion ........................................         333,324          650,002               --
Deferred rent ..............................................         174,705          104,918           96,581
Commitments ................................................
Stockholders' equity:
 Convertible   Preferred  Stock,   24,967,639  shares
   authorized; 24,203,931, 24,492,639 and 24,492,639
   shares issued and outstandin at December 31, 1998,
   1999 and March 31, 2000, respectively;  liquidation
   preference -- $40,909,587, $41,909,587 and $41,909,587
   at December 31, 1998 and 1999
   and March 31, 2000, respectively.........................      39,519,431       41,330,800       41,330,800
 Common stock, 37,563,708 shares authorized; 3,533,556,
   3,695,228 and 4,569,873 shares issued and outstanding
   at December 31, 1998, 1999 and March 31, 2000,
   respectively ............................................       2,720,121        3,795,460       11,313,761
Deferred compensation ......................................        (922,892)      (1,272,014)      (7,843,407)
Notes receivable from stockholders .........................         (95,600)         (95,600)        (133,100)
Accumulated other comprehensive income .....................           6,226               --               --
Accumulated deficit ........................................     (29,101,849)     (37,776,084)     (41,256,683)
                                                               -------------    -------------    -------------
 Total stockholders' equity ................................      12,125,437        5,982,562        3,411,371
                                                               -------------    -------------    -------------
 Total liabilities and stockholders' equity ................   $  19,558,219    $  14,538,865    $  11,649,718
                                                               =============    =============    =============
</TABLE>

                            SEE ACCOMPANYING NOTES.

                                       F-3
<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                            STATEMENTS OF OPERATIONS





<TABLE>
<CAPTION>
                                                    YEARS ENDED DECEMBER 31,               THREE MONTH ENDED MARCH 31,
                                         ----------------------------------------------- -------------------------------
                                               1997            1998            1999            1999            2000
                                         --------------- --------------- --------------- --------------- ---------------
                                                                                                   (UNAUDITED)
<S>                                      <C>             <C>             <C>             <C>             <C>
Revenue under collaborative
 agreements:
 Related party .........................  $    250,000    $  3,000,000    $  4,525,000    $    750,000    $  1,675,000
 Unrelated parties .....................     7,065,356      12,027,064       6,695,715       2,019,755         939,864
Grant income ...........................       264,257         387,178         527,610         153,290          55,862
                                          ------------    ------------    ------------    ------------    ------------
   Total Revenue .......................     7,579,613      15,414,242      11,748,325       2,923,045       2,670,726
                                          ------------    ------------    ------------    ------------    ------------
Expenses:
 Research and development ..............    10,337,318      15,572,627      16,747,627       4,346,239       5,167,494
 General and administrative ............     2,791,084       4,798,262       3,010,975         808,623       1,036,714
                                          ------------    ------------    ------------    ------------    ------------
   Total Expenses ......................    13,128,402      20,370,889      19,758,602       5,154,862       6,204,208
                                          ------------    ------------    ------------    ------------    ------------
Loss from operations ...................    (5,548,789)     (4,956,647)     (8,010,277)     (2,231,817)     (3,533,482)
Interest income ........................       325,529       1,052,854         607,413         144,419         115,766
Interest expense .......................      (516,709)       (452,609)       (452,884)       (126,219)        (62,883)
                                          ------------    ------------    ------------    ------------    ------------
Net loss ...............................    (5,739,969)     (4,356,402)     (7,855,748)     (2,213,617)     (3,480,599)
Inputed dividend on preferred stock.....            --              --        (818,487)             --              --
                                          ------------    ------------    ------------    ------------    ------------
Net loss applicable to common
 shareholders ..........................  $ (5,739,969)   $ (4,356,402)   $ (8,674,235)   $ (2,213,617)   $ (3,480,599)
                                          ============    ============    ============    ============    ============
Historical net loss per share
 applicable to common
 shareholders, basic and diluted .......  $      (2.82)   $      (1.65)   $      (2.64)   $      (0.71)   $      (0.98)
                                          ============    ============    ============    ============    ============
Weighted average shares outstanding,
 basic and diluted .....................     2,032,385       2,636,087       3,282,083       3,112,412       3,537,909
                                          ============    ============    ============    ============    ============
</TABLE>

                            SEE ACCOMPANYING NOTES.

                                       F-4
<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                       STATEMENTS OF STOCKHOLDERS' EQUITY



<TABLE>
<CAPTION>
                                                       CONVERTIBLE
                                                     PREFERRED STOCK              COMMON STOCK
                                              ---------------------------- --------------------------
                                                 SHARES         AMOUNT        SHARES       AMOUNT
                                              ------------ --------------- ----------- --------------
<S>                                           <C>          <C>             <C>         <C>
Balance at December 31, 1996 ................  14,793,324   $ 20,380,220    2,088,099   $   137,608
 Issuance of Series D preferred stock .......     232,601             --           --            --
 Issuance of Series E preferred stock .......   6,455,493     10,977,131           --            --
 Issuance of Series F preferred stock .......   2,722,513      8,162,080           --            --
 Issuance of common stock, net of
  repurchases ...............................          --             --      546,223        99,436
 Issuance of common stock for technology
  and services ..............................          --             --       22,500            --
 Deferred compensation ......................          --             --           --       615,855
 Amortization of deferred compensation ......          --             --           --            --
 Net loss ...................................          --             --           --            --
 Unrealized gain on available for sale
  securities ................................          --             --           --            --
 Comprehensive loss .........................          --             --           --            --
                                               ----------   ------------    ---------   -----------
Balance at December 31, 1997 ................  24,203,931     39,519,431    2,656,822       852,899
 Issuance of common stock, net of
  repurchases ...............................          --             --      611,734       121,052
 Issuance of common stock for
  technology ................................          --             --      265,000       727,000
 Deferred compensation ......................          --             --           --     1,019,170
 Amortization of deferred compensation ......          --             --           --            --
 Net loss ...................................          --             --           --            --
 Unrealized loss on available for sale
  securities ................................          --             --           --            --
 Comprehensive loss .........................          --             --           --            --
                                               ----------   ------------    ---------   -----------
Balance at December 31, 1998 ................  24,203,931     39,519,431    3,533,556     2,720,121
 Issuance of Series F-1 preferred stock .....     288,708        992,882           --            --
 Issuance of common stock, net of
  repurchases ...............................          --             --      160,248        26,177
 Deferred compensation ......................          --             --           --     1,024,244
 Amortization of deferred compensation ......          --             --           --            --
 Issuance of common stock and options
  for services ..............................          --             --        1,424        24,918
 Imputed dividend on Series F-1
  preferred stock ...........................          --        818,487           --            --
 Net loss ...................................          --             --           --            --
 Unrealized loss on available for sale
  securities ................................          --             --           --            --
 Comprehensive loss .........................          --             --           --            --
                                               ----------   ------------    ---------   -----------
Balance at December 31, 1999 ................  24,492,639     41,330,800    3,695,228     3,795,460
 Issuance of common stock, net of
  repurchases (unaudited)....................          --             --      874,645       286,008
 Deferred compensation (unaudited)...........          --             --           --     7,232,293
 Amortization of deferred compensation
 (unaudited).................................          --             --           --            --
 Net loss (unaudited)........................          --             --           --            --
 Unrealized loss on available for sale
  securities (unaudited).....................          --             --           --            --
 Comprehensive loss (unaudited)..............          --             --           --            --
                                               ----------   ------------    ---------   -----------
Balance at March 31, 2000 (unaudited)........  24,492,639   $ 41,330,800    4,569,873   $11,313,761
                                               ==========   ============    =========   ===========



<CAPTION>
                                                                    NOTES       ACCUMULATED
                                                                 RECEIVABLE        OTHER                             TOTAL
                                                  DEFERRED          FROM       COMPREHENSIVE     ACCUMULATED     STOCKHOLDERS'
                                                COMPENSATION    STOCKHOLDERS   INCOME (LOSS)       DEFICIT           EQUITY
                                              ---------------- -------------- --------------- ----------------- ---------------
<S>                                           <C>              <C>            <C>             <C>               <C>
Balance at December 31, 1996 ................   $         --     $       --     $       --      $ (19,005,478)   $   1,512,350
 Issuance of Series D preferred stock .......             --             --             --                 --               --
 Issuance of Series E preferred stock .......             --             --             --                 --       10,977,131
 Issuance of Series F preferred stock .......             --             --             --                 --        8,162,080
 Issuance of common stock, net of
  repurchases ...............................             --             --             --                 --           99,436
 Issuance of common stock for technology
  and services ..............................             --             --             --                 --               --
 Deferred compensation ......................       (615,855)            --             --                 --               --
 Amortization of deferred compensation ......        104,345             --             --                 --          104,345
 Net loss ...................................             --             --             --         (5,739,969)      (5,739,969)
 Unrealized gain on available for sale
  securities ................................             --             --         48,341                 --           48,341
                                                                                                                 -------------
 Comprehensive loss .........................             --             --             --                 --       (5,691,628)
                                                ------------     ----------     ----------      -------------    -------------
Balance at December 31, 1997 ................       (511,510)            --         48,341        (24,745,447)      15,163,714
 Issuance of common stock, net of
  repurchases ...............................             --        (95,600)            --                 --           25,452
 Issuance of common stock for
  technology ................................             --             --             --                 --          727,000
 Deferred compensation ......................     (1,019,170)            --             --                 --               --
 Amortization of deferred compensation ......        607,788             --             --                 --          607,788
 Net loss ...................................             --             --             --         (4,356,402)      (4,356,402)
 Unrealized loss on available for sale
  securities ................................             --             --        (42,115)                --          (42,115)
                                                                                                                 -------------
 Comprehensive loss .........................             --             --             --                 --       (4,398,517)
                                                ------------     ----------     ----------      -------------    -------------
Balance at December 31, 1998 ................       (922,892)       (95,600)         6,226        (29,101,849)      12,125,437
 Issuance of Series F-1 preferred stock .....             --             --             --                 --          992,882
 Issuance of common stock, net of
  repurchases ...............................             --             --             --                 --           26,177
 Deferred compensation ......................     (1,024,244)            --             --                 --               --
 Amortization of deferred compensation ......        675,122             --             --                 --          675,122
 Issuance of common stock and options
  for services ..............................             --             --             --                 --           24,918
 Imputed dividend on Series F-1
  preferred stock ...........................             --             --             --           (818,487)              --
 Net loss ...................................             --             --             --         (7,855,748)      (7,855,748)
 Unrealized loss on available for sale
  securities ................................             --             --         (6,226)                --           (6,226)
                                                                                                                 -------------
 Comprehensive loss .........................             --             --             --                 --       (7,861,974)
                                                ------------     ----------     ----------      -------------    -------------
Balance at December 31, 1999 ................     (1,272,014)       (95,600)            --        (37,776,084)       5,982,562
 Issuance of common stock, net of
  repurchases ...............................             --        (37,500)            --                 --          248,508
 Deferred compensation ......................     (7,232,293)            --             --                 --               --
 Amortization of deferred compensation ......        660,900             --             --                 --          660,900
 Net loss ...................................             --             --             --         (3,480,599)      (3,480,599)
 Unrealized loss on available for sale
  securities ................................             --             --             --                 --               --
                                                                                                                 -------------
 Comprehensive loss .........................             --             --             --                 --       (3,480,599)
                                                ------------     ----------     ----------      -------------    -------------
Balance at March 31, 2000 ...................   $ (7,843,407)    $ (133,100)    $       --      $ (41,256,683)   $   3,411,371
                                                ============     ==========     ==========      =============    =============
</TABLE>

                            SEE ACCOMPANYING NOTES.

                                       F-5
<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                            STATEMENTS OF CASH FLOWS





<TABLE>
<CAPTION>
                                                    YEARS ENDED DECEMBER 31,                THREE MONTHS ENDED MARCH 31,
                                       -------------------------------------------------- ---------------------------------
                                             1997             1998             1999             1999             2000
                                       ---------------- ---------------- ---------------- ---------------- ----------------
                                                                                                     (UNAUDITED)
<S>                                    <C>              <C>              <C>              <C>              <C>
OPERATING ACTIVITIES
Net loss .............................  $  (5,739,969)   $  (4,356,402)   $  (7,855,748)    $ (2,213,858)    $ (3,480,599)
 Adjustments to reconcile net loss to
  net cash used for operating activities:
   Depreciation and amortization......        879,327        1,498,312        1,711,501          365,528          428,118
   Amortization of interest
    expense related to warrants.......         47,142           47,142           47,142           11,786           11,786
   Amortization of deferred
    compensation .....................        104,345          607,788          675,122          139,704          660,900
   Amortization of purchased
    technology .......................             --           83,332          333,330           83,334           84,334
   Common stock and stock
    options issued for technology
    and services .....................         14,600            7,000           24,918               --           36,405
   Deferred revenue under
    collaborative agreements .........      1,363,134       (2,334,111)       2,068,693        1,389,120         (574,997)
   Deferred rent .....................         10,316           96,538          (69,787)         (18,558)          (8,337)
 Changes in operating assets and
  liabilities:
   Other current assets ..............        246,997         (354,667)          98,129           63,791         (591,036)
   Accounts payable ..................       (158,004)         193,253          434,293          460,016         (157,772)
   Accrued liabilities ...............        895,120         (335,235)        (350,030)        (391,835)         865,288
                                        -------------    -------------    -------------     ------------     ------------
    Net cash flows used for
     operating activities ............     (2,336,992)      (4,847,050)      (2,882,437)        (110,972)      (2,725,910)
                                        -------------    -------------    -------------     ------------     ------------
INVESTING ACTIVITIES
Purchases of short-term
 investments .........................    (12,081,165)     (15,585,368)     (11,642,049)      (2,804,301)      (2,262,192)
Maturities of short-term
 investments .........................             --       21,216,533       15,285,956        5,670,968        4,546,059
Purchases of property and
 equipment ...........................       (630,220)      (1,400,252)         (92,979)        (342,780)        (123,496)
Purchase of technology ...............             --         (280,000)              --               --               --
Other assets .........................        341,038         (117,501)         (37,161)           1,057            8,670
                                        -------------    -------------    -------------     ------------     ------------
    Net cash flows provided by
     (used for) investing
     activities ......................    (12,370,347)       3,833,412        3,513,767        2,524,944        2,169,041
                                        -------------    -------------    -------------     ------------     ------------
FINANCING ACTIVITIES
Principal payments on obligations
 under capital leases, equipment
 notes payable and promissory
 note ................................     (1,239,935)      (1,251,920)      (1,532,918)        (160,619)        (453,924)
Issuance of preferred stock, net .....     19,139,211               --          992,882               --               --
Issuance of common stock, net ........         84,836           25,452           26,177            8,760          212,103
                                        -------------    -------------    -------------     ------------     ------------
    Net cash flows provided by
     (used for) financing
     activities ......................     17,984,112       (1,226,468)        (513,859)        (151,859)        (241,821)
                                        -------------    -------------    -------------     ------------     ------------
Increase (decrease) in cash and
 cash equivalents ....................      3,276,773       (2,240,106)         117,471        2,262,113         (798,690)
Cash and cash equivalents at
 beginning of year ...................      5,459,696        8,736,469        6,496,363        6,496,363        6,613,834
                                        -------------    -------------    -------------     ------------     ------------
Cash and cash equivalents at end
 of year .............................  $   8,736,469    $   6,496,363    $   6,613,834     $  8,758,476     $  5,815,144
                                        =============    =============    =============     ============     ============
</TABLE>

                                       F-6
<PAGE>


<TABLE>
<CAPTION>
                                              YEARS ENDED DECEMBER 31,             THREE MONTHS ENDED MARCH 31,
                                    --------------------------------------------   ----------------------------
                                        1997           1998            1999            1999            2000
                                    -----------   -------------   --------------   ------------   -------------
                                                                                          (UNAUDITED)
<S>                                 <C>           <C>             <C>              <C>            <C>
SUPPLEMENTAL DISCLOSURE OF CASH
 FLOW INFORMATION:
Interest paid ...................    $469,565      $  395,462       $  452,884       $ 62,883      $   62,883
                                     ========      ==========       ==========       ========      ==========
SUPPLEMENTAL SCHEDULE OF NONCASH
 INVESTING AND FINANCING
 ACTIVITIES:
Capital lease obligations entered
 into for equipment .............    $221,507      $2,343,033       $  526,128       $ 79,604      $       --
                                     ========      ==========       ==========       ========      ==========
Issuance of common stock for
 technology .....................    $     --      $  720,000       $       --       $     --      $       --
                                     ========      ==========       ==========       ========      ==========
Issuance of common stock for
 promissory notes from
 stockholders ...................    $     --      $   95,600       $       --       $     --      $   37,500
                                     ========      ==========       ==========       ========      ==========
Comprehensive income (loss) on
 investments ....................    $ 48,341      $  (42,115)      $   (6,226)      $ (6,226)     $       --
                                     ========      ==========       ==========       ========      ==========
Deferred compensation related to
 stock options ..................    $615,855      $1,019,170       $1,024,244       $120,391      $7,232,293
                                     ========      ==========       ==========       ========      ==========
Imputed dividend on Series F-1
 preferred stock ................    $     --      $       --       $  818,487       $     --      $       --
                                     ========      ==========       ==========       ========      ==========
</TABLE>


                                       F-7
<PAGE>

                         SIGNAL PHARMACEUTICALS, INC.
                          NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)


1. ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES


ORGANIZATION AND BUSINESS ACTIVITY

Signal Pharmaceuticals, Inc. ("Signal" or the "Company") is an integrated drug
discovery and development company focused on identifying new classes of small
molecule drugs that regulate disease-associated genes. Utilizing biological
information from the field of human genomics, the Company applies advanced
cellular, molecular and genomic technologies to map gene regulating pathways in
cells and to identify proprietary molecular targets that control genes and
result in disease. Signal is advancing the application of genomics beyond
identifying and elucidating the function of genes to designing novel classes of
disease-modifying drugs that selectively regulate the activation of
disease-causing genes.


USE OF ESTIMATES

The preparation of financial statements in conformity with generally accepted
accounting principles requires management to make estimates and assumptions that
affect the reported amounts of assets and liabilities and related disclosures at
the date of the financial statements, and the amounts of revenues and expenses
reported during the period. Actual results could differ from those estimates.


CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS

The Company considers instruments purchased with an original maturity of three
months or less, principally a money market account and U.S. government and
corporate debt securities, to be cash equivalents.

All investment securities are classified as available-for-sale, and are carried
at fair value. Unrealized gains and losses, if any, are reported in a separate
component of stockholders' equity. The cost of debt securities is adjusted for
amortization of premiums and accretion of discounts to maturity. The
amortization, along with realized gains and losses, is included in interest
income. The cost of securities sold is based on the specific identification
method.


INTERIM FINANCIAL INFORMATION

The financial information as of March 31, 2000 and for the three months ended
March 31, 1999 and 2000 is unaudited and includes all adjustments, consisting
only of normal recurring adjustments, that the Company's management considers
necessary for the fair presentation of the Company's operating results and cash
flows for such periods. Results for the three-month period ended March 31, 2000
are not necessarily indicative of results to be expected for the full fiscal
year 2000 or any future period.


CONCENTRATION OF CREDIT RISK

Cash, cash equivalents, and short-term investments are financial instruments
that potentially subject the Company to concentration of credit risk. The
Company invests its excess cash primarily in U.S. government securities and
marketable debt securities of financial institutions and corporations with
strong credit ratings. The Company also has established guidelines relative to
diversification and maturities to maintain safety and liquidity. These
guidelines are reviewed periodically and may be modified to take advantage of
trends in yields and interest rates. Pursuant to Company policy, the Company has
historically held the investments to maturity. However, the Company has the
ability to sell these investments before maturity and has therefore classified
the investments as available for sale. The Company has not experienced any
significant losses on its investments.


                                       F-8
<PAGE>

                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)


FINANCIAL INSTRUMENTS

The fair value of the financial instruments approximates their carrying value.


PROPERTY AND EQUIPMENT

Property and equipment are stated at cost and depreciated over the estimated
useful lives of the assets (three to five years) using the straight-line method.
Leasehold improvements are stated at cost and amortized on a straight-line basis
over the shorter of the estimated useful life of the assets or the lease term.


LICENSED TECHNOLOGY

Licensed technology is stated at cost and depreciated over the estimated useful
life of three years using the straight-line method. The licensed technology is
reported net of accumulated amortization of $83,332, $416,662 and $500,996 as of
December 31, 1998 and 1999 and March 31, 2000, respectively.


IMPAIRMENT OF LONG-LIVED ASSETS

In accordance with SFAS No. 121, Accounting for the Impairment of Long-Lived
Assets and for Long-Lived Assets to be Disposed of, if indicators of impairment
exist, the Company assesses the recoverability of the affected long-lived assets
by determining whether the carrying value of such assets can be recovered
through undiscounted future operating cash flows. If impairment is indicated,
the Company will value the asset at fair value. While the Company's current and
historical operating and cash flow losses are indicators of impairment, the
Company believes the future cash flows to be received from the long-lived assets
will exceed the assets' carrying value, and accordingly the Company has not
recognized any impairment losses through March 31, 2000.


REVENUE RECOGNITION

Contract revenue is recognized ratably over the period during which the research
is conducted, which approximates the actual costs incurred to perform the
research services. Up-front license fees received under these agreements are
recorded as deferred revenue and recognized ratably over the initial term of the
contract. If the initial term of the agreement is subsequently modified by the
collaborator, the period over which the up-front license fee is recognized is
modified accordingly on a prospective basis. Revenues from the achievement of
research and development milestones will be recognized when and if the
milestones are achieved. Continuation of certain contracts and grants are
dependent upon the Company achieving specific contractual milestones; however,
none of the payments received to date are refundable regardless of the outcome
of the project. Grant revenue is recognized in accordance with the terms of the
grant and as services are performed, which generally equals the related research
and development expense.

Axys Pharmaceutical ("Axys") is a related party, as the chief executive officer
of Axys serves on the Board of Directors of the Company. Therefore, revenues of
$625,000 recognized in 1999 and the three months ended March 31, 2000 from Axys
are classified as related party revenue.

Ares Serono S.A. ("Ares") is a related party, based on its ownership interest in
the Company. Therefore, revenues of $3,000,000, $3,900,000 and $1,050,000
recognized from Ares in 1998, 1999 and the three months ended March 31, 2000,
respectively, are classified as related party revenue. The Company does not have
the right or the obligation to repurchase any of the rights provided to Ares, or
to refund any research payments received from Ares under the collaboration, nor
does it intend to do so.


                                       F-9
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS


 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

The Company's revenue is concentrated among a small number of customers, as
follows:

                                           YEAR ENDED         THREE MONTHS ENDED
                                          DECEMBER 31,            MARCH 31,
                                   -------------------------- -----------------
                                     1997     1998     1999     1999     2000
                                   -------- -------- -------- -------- --------
                                                                 (UNAUDITED)
DuPont .........................     --       12%      20%      20%      23%
  Ares ...........................      *       19%      33%      26%      39%
  Roche Bioscience ...............     21%       *        *        *        *
  Organon ........................     34%      19%      13%      25%      --
  Nippon Kayaku ..................     --       12%      20%      17%      11%
  Tanabe .........................     39%      27%      --       --       --
  Axys ...........................     --       --        *       --       23%

* Amount earned represents less than 10% of revenues for the period.

     The Company's revenue under collaborative agreements is derived from the
following:

<TABLE>
<CAPTION>
                                                               YEARS ENDED DECEMBER 31,          THREE MONTHS ENDED MARCH 31,
                                                       ----------------------------------------- ----------------------------
                                                            1997          1998          1999          1999          2000
                                                       ------------- ------------- ------------- ------------- -------------
                                                                                                         (UNAUDITED)
<S>                                                    <C>           <C>           <C>           <C>           <C>
License fees from collaborative agreements ...........  $  724,992    $ 3,139,566   $ 1,858,332   $  208,329    $  658,329
Research and development revenues under
 collaborative agreements ............................   6,590,364     11,887,498     9,362,383    2,561,426     1,956,535
                                                        ----------    -----------   -----------   ----------    ----------
Total revenue under collaborative agreements .........  $7,315,356    $15,027,064   $11,220,715   $2,769,755    $2,614,864
                                                        ==========    ===========   ===========   ==========    ==========
</TABLE>

RESEARCH AND DEVELOPMENT COSTS

Research and development costs are expensed as incurred.

SOFTWARE COSTS

Purchased software is capitalized at cost and amortized over the estimated
useful life, generally three years. The Company has no significant
internally-developed software.

STOCK-BASED COMPENSATION

As permitted by SFAS 123, Accounting for Stock-Based Compensation, the Company
has elected to follow Accounting Principles Board Opinion No. 25, Accounting for
Stock Issued to Employees, and related Interpretations ("APB 25") in accounting
for its employee stock options. Under APB 25, when the exercise price of the
Company's employee stock options equals the fair value of the underlying stock
on the date of grant, no compensation expense is recognized.

When the exercise price of the employee or director stock options is less than
the fair value of the underlying stock on the grant date, the Company records
deferred compensation for the difference and amortizes this amount to expense in
accordance with FASB Interpretation No. 28 ("FIN 28") over the vesting period of
the options. Options or stock awards issued to non-employees and consultants are
recorded at their fair value as determined in accordance with SFAS No. 123 and
EITF 96-18 and recognized over the related service period.

COMPREHENSIVE INCOME (LOSS)

In accordance with SFAS No. 130, Reporting Comprehensive Income, unrealized
gains or losses on the Company's available-for-sale securities and foreign
currency translation adjustments, which prior to adoption were reported
separately in stockholders' equity, are included in other comprehensive income
(loss).

                                      F-10
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

SEGMENT REPORTING

SFAS No. 131, Disclosure About Segments of an Enterprise and Related
Information, requires the use of a management approach in identifying and
disclosing financial information about segments of an enterprise. Management has
determined that the Company operates in one business segment.

NET LOSS PER SHARE

In accordance with SFAS No. 128, Earnings Per Share, and SEC Staff Accounting
Bulletin (or SAB) No. 98, basic net loss per share is computed by dividing the
net loss for the period by the weighted average number of common shares
outstanding during the period. Diluted net loss per share is computed by
dividing the net loss for the period by the weighted average number of common
and common equivalent shares outstanding during the period. Potentially dilutive
securities composed of incremental common shares issuable upon the exercise of
stock options and warrants, and common shares issuable on conversion of
preferred stock, were excluded from historical diluted loss per share because of
their anti-dilutive effect.

Under the provisions of SAB No. 98, common shares issued for nominal
consideration, if any, would be included in the per share calculations as if
they were outstanding for all periods presented. No common shares have been
issued for nominal consideration.

NEW ACCOUNTING PRONOUNCEMENTS

The Company expects to adopt SFAS No. 133, Accounting for Derivative Instruments
and Hedging Activities, effective January 1, 2001. SFAS No. 133 will require the
Company to recognize all derivatives on the balance sheet at fair value. The
Company does not anticipate that the adoption of the SFAS No. 133 will have a
significant effect on its results of operations or financial position.

2. BALANCE SHEET INFORMATION

INVESTMENTS

The following is a summary of the Company's cash, cash equivalents and
short-term investments, all of which mature within one year of the balance sheet
date:

<TABLE>
<CAPTION>
                                  DECEMBER 31, 1998                         DECEMBER 31, 1999
                      ------------------------------------------ ----------------------------------------
                                         GROSS                                      GROSS
                                      UNREALIZED     ESTIMATED                   UNREALIZED    ESTIMATED
                           COST          GAINS      FAIR VALUE        COST          GAINS     FAIR VALUE
                      -------------- ------------ -------------- -------------- ------------ ------------
<S>                   <C>            <C>          <C>            <C>            <C>          <C>
Cash ................ $ 6,496,363       $   --    $ 6,496,363    $ 4,636,426         $--     $4,636,426
Corporate debt
 securities .........   6,450,000        6,226      6,456,226      4,783,501          --      4,783,501
                      -----------       ------    -----------    -----------         ---     ----------
                      $12,946,363       $6,226    $12,952,589    $ 9,419,927         $--     $9,419,927
                      ===========       ======    ===========    ===========         ===     ==========
<CAPTION>
                                    MARCH 31, 2000
                      ------------------------------------------
                                      (UNAUDITED)
                                         GROSS
                                      UNREALIZED     ESTIMATED
                           COST          GAINS      FAIR VALUE
                      -------------- ------------ --------------
<S>                   <C>            <C>          <C>
Cash ................ $ 6,337,370         $--     $ 6,337,370
Corporate debt
 securities .........          --          --              --
                      -----------         ---     -----------
                      $ 6,337,370         $--     $ 6,337,370
                      ===========         ===     ===========
</TABLE>

There were no gross realized gains or losses on sales of available-for-sale
securities for the years ended December 31, 1998 or 1999 or the three months
ended March 31, 2000. The gross unrealized gains of $6,226, $0 and $0 at
December 31, 1998 and 1999 and March 31, 2000, respectively, are reflected as a
separate component of stockholders' equity. The unrealized gain had no cash
effect and therefore is not reflected in the statement of cash flows.

                                      F-11
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS


 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

PROPERTY AND EQUIPMENT

Property and equipment consist of the following:

<TABLE>
<CAPTION>
                                                              DECEMBER 31,              MARCH 31,
                                                     ------------------------------- ---------------
                                                           1998            1999            2000
                                                     --------------- --------------- ---------------
                                                                                       (UNAUDITED)
<S>                                                  <C>             <C>             <C>
     Machinery and equipment .......................  $  4,818,472    $  5,328,565    $  5,387,847
     Office furniture and equipment ................     1,597,943       1,655,263       1,679,718
     Leasehold improvements ........................     1,915,689       1,967,383       2,007,142
                                                      ------------    ------------    ------------
                                                         8,332,104       8,951,211       9,074,707
     Less accumulated depreciation and amortization.    (3,834,563)     (5,546,064)     (5,974,182)
                                                      ------------    ------------    ------------
                                                      $  4,497,541    $  3,405,147    $  3,100,525
                                                      ============    ============    ============
</TABLE>

DEPOSITS AND OTHER ASSETS

Deposits and other assets consist of the following:

                                     DECEMBER 31,        MARCH 31,
                                 --------------------- ------------
                                    1998       1999        2000
                                 ---------- ---------- ------------
                                                        (UNAUDITED)
       Deposits ................  $ 73,520   $ 52,605    $ 45,430
       Restricted cash .........   150,000    150,000     150,000
                                  --------   --------    --------
                                  $223,520   $202,605    $195,430
                                  ========   ========    ========

3. COMMITMENTS

LEASES

The Company leases its office and research facilities under three operating
lease agreements. The minimum annual rents are subject to specified annual
rental increases. The Company also reimburses the lessor for taxes, insurance
and operating costs associated with the leases. Under the terms of the lease,
the Company has an outstanding letter of credit for $150,000 in favor of the
lessor, which is fully collateralized by cash. Accordingly, such cash is
classified as restricted in the balance sheet.

In addition, the Company leases certain machinery and equipment and office
furniture under capital leases with three year terms and options to extend the
lease term to five years.

LONG-TERM DEBT

In November 1996, the Company issued a secured promissory note for $3,000,000.
The proceeds of the note payable were used for general corporate purposes and
working capital. The note payable accrues interest at a rate of 14%, is due May
22, 2000, and is secured by certain assets of the Company.

In conjunction with the issuance of the promissory note, the Company issued the
creditor a warrant to purchase 250,000 shares of Series C-1 Preferred Stock at a
price of $2.10 per share. The warrant expires at the earliest of ten years from
the date of grant or five years from the date of an initial public offering. The
warrant was valued at $165,000, which has been recorded as a discount on the
related debt. The value of the warrant is being amortized as interest expense
over the period of the debt.

                                      F-12
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS


 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

Annual future minimum lease and equipment note payments as of December 31, 1999
are as follows:

<TABLE>
<CAPTION>
                                                                                 OBLIGATIONS
                                                                                    UNDER
                                                                                   CAPITAL
                                                                                 LEASES AND
                                                                   OPERATING      EQUIPMENT
YEAR ENDING DECEMBER 31,                                             LEASES     NOTES PAYABLE
---------------------------------------------------------------- ------------- --------------
<S>                                                              <C>           <C>
     2000 ......................................................  $  935,032     $  964,616
     2001 ......................................................     430,502        967,662
     2002 ......................................................     432,295        857,701
     2003 ......................................................     443,370         61,861
                                                                  ----------     ----------
       Total minimum lease and equipment note payments .........  $2,241,199      2,851,840
                                                                  ==========
    Less amount representing interest ..........................                   (315,778)
                                                                                 ----------
    Present value of remaining minimum capital lease and
      equipment lease line payments ............................                  2,536,062
    Less amount due in one year ................................                   (730,765)
                                                                                 ----------
    Long-term portion of obligations under capital leases and
      equipment notes payable ..................................                 $1,805,297
                                                                                 ==========
</TABLE>

Rent expense for equipment and facility leases was $784,337, $809,028, $771,302
and $244,696 for the years ended December 31, 1997, 1998 and 1999, and the three
months ended March 31, 2000, respectively.

Cost and accumulated depreciation of equipment under capital leases and
equipment notes payable were as follows:



<TABLE>
<CAPTION>
                                                         ACCUMULATED
                                               COST      DEPRECIATION
                                          ------------- -------------
<S>                                       <C>           <C>
     December 31, 1998 ..................  $2,943,246    $  594,452
     December 31, 1999 ..................  $3,458,659    $1,213,886
     March 31, 2000 (unaudited) .........  $2,872,076    $  938,116
</TABLE>

4. SPONSORED RESEARCH AND LICENSE AGREEMENTS

In connection with certain license agreements, the Company paid fees of $196,333
and $87,000 for the years ended December 31, 1998 and 1999, respectively, which
were charged to research and development. In addition, the Company paid $280,000
in cash and issued 240,000 shares of common stock related to a license agreement
with the University of Massachusetts in 1998. The Company determined the value
of the common shares issued as $720,000 and capitalized the total consideration
of $1.0 million as licensed technology. The Company has future commitments to
pay up to an additional $4,100,000 to the licensees based on the achievement of
certain milestones, as well as royalties upon commercial sales, if any, of
certain products. Such fees or milestone payments may also involve the issuance
of up to 60,000 shares of common stock, which would be recorded at the fair
value at the date of issuance.

Axys

On October 15, 1999, the Company entered into a two-year collaborative research
and license agreement with Axys to develop and commercialize certain compounds
for use in the prevention and/or treatment of certain human diseases. The
Company received an initial non-refundable license fee of $2,000,000 and will
receive additional payments based on the achievement of certain program
milestones, as well as royalties upon commercial sales of certain products, if
any. We may exercise a profit share option in the United States and possibly
other territories at a predetermined point during development in lieu of
royalties on product sales. In addition, Axys has agreed to pay the Company
certain amounts for the full time equivalent personnel working on the research.

                                      F-13
<PAGE>

                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

Nippon Kayaku


In February 1998, the Company entered into a two-year collaborative research and
license agreement with Nippon Kayaku to develop and commercialize products based
on or derived from a compound supplied by Nippon Kayaku for the treatment and
prevention of diseases and disorders of the CNS and PNS. Nippon Kayaku has
agreed to pay the Company certain amounts for the full-time equivalent personnel
working on the research. Each party is obligated to pay the other royalties on
future product sales arising from the collaboration.


In February 2000, following the initial research phase of the collaboration, the
Company executed an interim agreement with Nippon Kayaku under which the Company
agreed to enter into a joint agreement to develop and commercialize
neuroprotectant drugs for PNS and CNS disorders.


In July 2000, Signal and Nippon Kayaku mutually agreed to conclude their
collaboration. Nippon Kayaku was granted a worldwide, royalty-free license to
certain compounds involved in the collaboration.


Dupont


On December 26, 1997, the Company entered into a three-year collaborative
research and license agreement with DuPont Pharmaceuticals ("DuPont") to develop
and commercialize novel products for the treatment and prevention of human
immunodeficiency virus and hepatitis C virus infection. The Company received an
initial non-refundable license fee of $1,000,000 and will receive additional
payments based on the achievement of certain program milestones, as well as
royalties upon commercial sales of certain products, if any. In addition, DuPont
has agreed to pay the Company certain amounts for the full time equivalent
personnel working on the research. Due to the Company's achievement of a certain
milestone in 1999, DuPont purchased 288,708 shares of Series F-1 Preferred Stock
for total cash proceeds of $1,000,000. In accordance with EITF 98-5 the Company
recognized an imputed dividend of $818,487 to reflect a beneficial conversion
feature on these preferred shares.


Ares-Serono


On November 25, 1997, the Company entered into a three-year collaborative
research, development and license agreement with Ares to perform research within
the field of the modulation of NF-kB. The Company will receive payments based on
the achievement of certain program milestones, as well as royalties upon
commercial sales of certain products, if any. In addition, Ares has agreed to
pay the Company certain amounts for the full time equivalent personnel working
on the research. In conjunction with the license agreement, Ares purchased
2,722,513 shares of the Company's Series F Preferred Stock at $3.01 per share
for a total of $8,194,761.


Roche Bioscience


On August 26, 1996, the Company entered into a three-year collaborative research
agreement with Roche Bioscience ("Roche") to conduct a joint research program to
develop human and rat nociceptive and/or sensory neuronal cell lines. The
Company received an initial non-refundable license fee of $500,000 and will
receive additional payments based on the achievement of certain program
milestones. In addition, Roche has paid the Company certain amounts for the full
time equivalent personnel working on the research. In 1999, the Company and
Roche agreed to conclude their collaboration; therefore, the Company has no
future performance obligations under this collaboration.


                                      F-14
<PAGE>

                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

Organon

On July 30, 1996, the Company entered into a three-year collaborative research
agreement with N.V. Organon ("Organon") to assist Organon in the discovery and
development of tissue-specific, estrogen-regulated genes. The Company received
an initial non-refundable license fee of $1,000,000 and will receive additional
payments based on the achievement of certain program milestones, as well as
royalties upon commercial sales of certain products, if any. In addition,
Organon has paid the Company certain amounts for the full time equivalent
personnel performing the research. In 1999, the Company and Organon agreed to
conclude their collaboration; therefore, the Company has no future performance
obligations under this collaboration.


Tanabe

From March 1996 to March 1998, Signal and Tanabe were engaged in a collaborative
program under which Tanabe funded certain research by Signal in target and drug
discovery in the fields of inflammatory disease and osteoporosis. In connection
with the collaboration, Tanabe paid Signal an initial $1,000,000 non-refundable
license fee and reimbursed Signal for research and development costs. Tanabe
also purchased 500,000 shares of Signal's Series D Preferred Stock at $4.00 per
share. Pursuant to certain anti-dilution provisions of the Series D Preferred
Stock agreement triggered by the sale of shares of the Company's Series E
Preferred Stock at $1.91 per share, the Company issued an additional 232,601
shares of Series D Preferred Stock to Tanabe during 1997.

In March 1998, Signal and Tanabe mutually agreed to conclude their collaboration
and Tanabe licensed from Signal a lead compound that was discovered during the
collaboration. Signal retained all other intellectual property rights, including
rights to all other drug targets and drug leads, created before or during the
collaboration. Tanabe paid an additional non-refundable fee of $1,800,000 to
Signal for the exclusive worldwide license to the lead compound and is obligated
to make payments to Signal based on the achievement of certain research and
development milestones and royalties on any future product sales. Signal has no
future performance obligations under this collaboration.


5. STOCKHOLDERS' EQUITY


CONVERTIBLE PREFERRED STOCK

A summary of the convertible preferred stock at December 31, 1999 and March 31,
2000 is as follows:





<TABLE>
<CAPTION>
                              SHARES ISSUED    PREFERENCE IN
                             AND OUTSTANDING    LIQUIDATION
                            ----------------- --------------
<S>                         <C>               <C>
  Series A ................      2,626,892     $ 2,626,892
  Series B ................      2,875,000       3,450,000
  Series C ................      8,791,432      12,308,005
  Series D ................        732,601       2,000,000
  Series E ................      6,455,493      12,329,929
  Series F ................      2,722,513       8,194,761
  Series F-1 ..............        288,708       1,000,000
                                 ---------     -----------
                                24,492,639     $41,909,587
                                ==========     ===========
</TABLE>

Each of the shares of Series A, B, C, D, E, F and F-1 preferred stock is
convertible on a one-for-one basis, at the option of the holder, into shares of
the Company's common stock. Therefore, 24,492,639 shares of common stock have
been reserved for issuance upon conversion of the preferred stock, subject to
certain anti-dilution adjustments. The preferred stock will convert
automatically upon the closing of an underwritten public offering of the
Company's common stock


                                      F-15
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

with proceeds to the Company of at least $15,000,000 and at a price not less
than $5.00 per share after adjustment for any stock splits. The holders of the
Series A, B, C, E and F preferred stock as a group are entitled to elect four
directors to the Board of Directors, and in all other matters the holder of each
share of preferred stock is entitled to one vote for each share of common stock
into which it would convert.


Annual dividends of $.08, $.10, $.11, $.32, $.15, $.24 and $.28 per share of
Series A, B, C, D, E, F and F-1 preferred stock, respectively, are payable
whenever funds are legally available and when and as declared by the Board of
Directors.


COMMON STOCK


In connection with certain stock purchase agreements, the Company has the option
to repurchase, at the original issue price, unvested shares in the event of
termination of employment or engagement. Shares issued under these agreements
generally vest over four to five years. At December 31, 1999 and March 31, 2000,
257,793 and 341,728 shares, respectively, were subject to repurchase by the
Company.


STOCK OPTION PLANS


In June 1993, the Company adopted the 1993 Founders' Stock Option Plan (the
"Founders' Plan"), under which 550,000 shares of common stock were reserved for
issuance upon exercise of options granted by the Company. The Founders' Plan
provides for the grant of incentive and nonstatutory options. The exercise price
of incentive stock options must equal at least the fair market value on the date
of grant, and the exercise price of nonstatutory stock options may be no less
than 85% of the fair market value on the date of grant. The maximum term of
options granted under the Founders' Plan is ten years. Options generally are
immediately exercisable. Common stock or options issued under the Founders' Plan
generally vest over five years. Unvested shares issued pursuant to the exercise
of options are subject to repurchase, at the original purchase price, in the
event of termination of employment or engagement.


In November 1993, the Company adopted the 1993 Stock Option Plan, under which
450,000 shares of the Company's common stock were reserved for issuance upon
exercise of options granted by the Company under provisions similar to the
Founders' Plan. In 1995 and 1996, the Company authorized an additional 1,000,000
and 1,050,000 shares, respectively, of the Company's common stock to be reserved
for issuance upon exercise of options granted by the Company under the 1993
Stock Option Plan.


In June 1997, the Company adopted the 1997 Stock Option Plan, under which
1,000,000 shares of common stock were reserved for issuance upon exercise of
options granted by the Company. In February 1998, the Company authorized an
additional 2,000,000 shares of the Company's common stock to be reserved for
issuance upon exercise of options granted by the Company under the 1997 Stock
Option Plan. The options contain similar provisions to those options issued
under the 1993 Founders' Stock Option Plan and the 1993 Stock Option Plan.


                                      F-16
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

A summary of the Company's stock option activity and related information for the
years ended December 31 follows:





<TABLE>
<CAPTION>
                                                                                                                 THREE
                                                                                                              MONTHS ENDED
                                                     YEARS ENDED DECEMBER 31                                 MARCH 31, 2000
                          ----------------------------------------------------------------------------- ------------------------
                                         WEIGHTED-                 WEIGHTED-                 WEIGHTED-                 WEIGHTED-
                                          AVERAGE                   AVERAGE                   AVERAGE                   AVERAGE
                                          EXERCISE                  EXERCISE                  EXERCISE                 EXERCISE
                             OPTIONS       PRICE       OPTIONS       PRICE       OPTIONS       PRICE       OPTIONS       PRICE
                             -------       -----       -------       -----       -------       -----       -------       -----
<S>                       <C>           <C>         <C>           <C>         <C>           <C>         <C>           <C>
Outstanding at
 beginning of period.....   1,592,300      $ .13      2,168,495      $ .20      3,264,200     $  .33      2,987,222    $   .36
Granted .................   1,246,695      $ .27      1,987,500      $ .43        350,200     $  .50      1,437,750    $  1.30
Exercised ...............    (555,090)     $ .15       (713,304)     $ .19       (161,998)    $  .15       (879,399)   $  1.04
Cancelled ...............    (115,410)     $ .16       (178,491)     $ .30       (465,180)    $  .38        (59,454)   $   .32
                            ---------      -----      ---------      -----      ---------     ------      ---------    -------
Outstanding at end of
 period .................   2,168,495      $ .20      3,264,200      $ .33      2,987,222     $  .36      3,486,119    $   .75
                            =========      =====      =========      =====      =========     ======      =========    =======
Vested options at end
 of period ..............     501,064      $ .11        539,650      $ .15      1,365,406     $  .32        811,637    $   .39
                            =========      =====      =========      =====      =========     ======      =========    =======
</TABLE>

Exercise prices for options outstanding as of March 31, 2000 ranged from $.10 to
$1.50. The weighted average remaining contractual life of those options at March
31, 2000 is 6.6 years. The weighted-average fair value of options granted in
1997, 1998 and 1999, using the minimum value pricing model, was $.07, $.11 and
$.11, respectively.

As of March 31, 2000, options for 2,358,433 common shares were available for
future grant.

The Company recorded $615,855, $1,019,170, $1,024,244 and $7,232,293 of deferred
compensation for options granted during the years ended December 31, 1997, 1998
and 1999 and the three months ended March 31, 2000, respectively, representing
the difference between the option exercise price and the estimated fair value of
the underlying stock for financial statement presentation purposes. The Company
is amortizing the deferred compensation over the vesting period of the options.
The Company recorded $104,345, $607,788, $675,122 and $660,900 of compensation
expense during the years ended December 31, 1997, 1998 and 1999 and the three
months ended March 31, 2000, respectively.

Pro forma information regarding net loss is required to be disclosed by SFAS
123, and has been determined as if the Company had accounted for its employee
stock options under the fair value method prescribed in that Statement. The fair
value of these options was estimated at the date of grant using the minimum
value pricing model with the following weighted-average assumptions for 1997,
1998 and 1999 and the three months ended March 31, 2000: risk-free interest rate
of 6%, dividend yield of 0%; and an expected life of four years.

The minimum value pricing model is similar to the Black-Scholes option valuation
model which was developed for use in estimating the fair value of traded options
which have no vesting restrictions and are fully transferable, except that it
excludes the factor for volatility. In addition, option valuation models require
the input of highly subjective assumptions. Because the Company's employee stock
options have characteristics significantly different from those of traded
options, and because changes in the subjective input assumptions can materially
affect the fair value estimate, in management's opinion, the existing models do
not necessarily provide a reliable single measure of the fair value of its
employee stock options.

For purposes of pro forma disclosures, the estimated fair value of the options
is amortized to expense over the vesting period of the related options. The
adjusted pro forma net loss for the years ended December 31, 1997, 1998 and 1999
was $5,757,845, $4,384,804 and $7,913,695, respectively. The effects are not
likely to be representative of the effects on pro forma net loss in future years
because it does not take into consideration pro forma compensation expense
related to grants made prior to 1996.


                                      F-17
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

COMMON SHARES RESERVED FOR FUTURE ISSUANCE


At March 31, 2000, the Company has reserved shares of common stock for future
issuance as follows:


<TABLE>
<S>                                                        <C>

       Conversion of convertible preferred stock .........  24,492,639
       Stock option plans ................................   5,844,552
       Warrants ..........................................     250,000
                                                            ----------
                                                            30,587,191
                                                            ==========

</TABLE>

6. INCOME TAXES

Significant components of the Company's deferred tax assets as of December 31,
1998 and 1999 are shown below. A valuation allowance of $15,290,000, of which
$2,779,000 is related to 1999, has been recognized as of December 31, 1999 to
offset the deferred tax assets as realization of such assets is uncertain.


<TABLE>
<CAPTION>
                                                                       DECEMBER 31,
                                                             ---------------------------------
<S>                                                          <C>              <C>
                                                                       1998             1999
                                                                       ----             ----
       DEFERRED TAX ASSETS:
       Capitalized research expenses .......................  $     965,000    $     921,000
       Net operating loss carryforwards ....................      9,276,000       11,389,000
       Research and development credits ....................      1,458,000        1,877,000
       Depreciation ........................................         57,000          952,000
       Other, net ..........................................        755,000          151,000
                                                              -------------    -------------
       Total deferred tax assets ...........................     12,511,000       15,290,000
       Valuation allowance for deferred tax assets .........    (12,511,000)     (15,290,000)
                                                              -------------    -------------
       Net deferred taxes ..................................  $          --    $          --
                                                              =============    =============

</TABLE>

At December 31, 1999, the Company has federal and California net operating loss
carryforwards of approximately $30,621,000 and $11,680,000, respectively. The
difference between the federal and California tax loss carryforwards is
attributable to the capitalization of research and development expenses for
California tax purposes and the fifty percent limitation on California loss
carryforwards prior to 1997. The federal tax loss carryforwards will begin
expiring in 2007, unless previously utilized. The California tax loss
carryforwards will continue to expire in 2000 (approximately $1,035,000 expired
in 1999). The Company also has federal and California research and development
tax credit carryforwards of approximately $1,368,000 and $783,000, respectively,
which will begin expiring in 2008 unless previously utilized.


Pursuant to Sections 382 and 383 of the Internal Revenue Code, the annual use of
the Company's net operating loss and credit carryforwards may be limited if a
cumulative change in ownership (as defined) of more than 50% occurs within a
three-year testing period.


7. SUBSEQUENT EVENT (UNAUDITED)


In January 2000, the Company's Board of Directors adopted the 2000 Equity
Incentive Plan, which amended the 1993 Stock Option Plans and the 1997 Stock
Option Plan. The Board of Directors also increased the share reserve of the 2000
Equity Incentive Plan to 9,050,000 shares.


                                      F-18
<PAGE>
                          SIGNAL PHARMACEUTICALS, INC.
                         NOTES TO FINANCIAL STATEMENTS

 (INFORMATION  SUBSEQUENT TO DECEMBER 31, 1999 AND  PERTAINING TO MARCH 31, 2000
       AND THE THREE MONTHS ENDED MARCH 31, 1999 AND 2000 IS UNAUDITED.)

In June 2000, Signal issued a secured promissory note for up to $5,000,000 that
can be borrowed against through December 31, 2000, as needed. The proceeds of
the note will be used for general corporate purposes and working capital. The
interest rate will float with the Treasury rate as the proceeds are drawn down
and then be fixed for the term, maintaining the spread. The note is payable in
either twelve or thirty-six monthly installments, at Signal's option, and is
secured by the assets of the Company. To date, Signal has not drawn down any
proceeds from the note. In conjunction with the issuance of the promissory note,
Signal issued the creditor a warrant to purchase up to 225,000 shares of Series
C-2 Preferred Stock at a price of $4.00 per share, of which 150,000 shares were
issuable under the warrant upon Signal's signing of a loan commitment letter in
May 2000, and the remaining 75,000 shares become issuable under the warrant upon
any additional borrowing against the note greater than $2.5 million. The warrant
expires ten years from the date of grant. Accordingly, the Company increased its
authorized shares of Preferred Stock from 24,742,639 to 24,967,639.

On June 29, 2000, the Company  entered into an agreement and plan of merger with
Celgene  Corporation  ("Celgene")  in  which  Celgene  will  acquire  all of the
outstanding  shares of Signal common and preferred stock for  approximately  3.7
million shares of Celgene common stock.  Signal  stockholders will receive .1257
of a share of common stock, par value $.01 per share, of Celgene in exchange for
each share of common stock of Signal.  The  acquisition  will be  accounted  for
using the pooling of interests method of accounting.


                                      F-19
<PAGE>

                                     PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS


ITEM 20. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     The General Corporation Law of the State of Delaware, or the DGCL, permits
Celgene and its stockholders to limit directors' exposure to liability for
certain breaches of the directors' fiduciary duty, either in a suit on behalf of
Celgene or in an action by stockholders of Celgene.

     The Certificate of Incorporation of Celgene, or the Charter, eliminates the
liability of directors of Celgene to Celgene or its stockholders for monetary
damages arising out of the directors' breach of their fiduciary duty of care.
The Charter also authorizes Celgene to indemnify its directors, officers,
incorporators, employees and agents with respect to certain costs, expenses, and
amounts incurred in connection with an action, suit or proceeding by reason of
the fact that such person was serving as a director, officer, incorporator,
employee or agent of Celgene. In addition, the Charter permits Celgene to
provide additional indemnification rights to its officers and directors and to
indemnify them to the greatest extent possible under the DGCL. Celgene has
entered into indemnification agreements with each of its officers and directors
and intends to enter into indemnification agreements with each of its future
officers and directors. Pursuant to such indemnification agreements, Celgene has
agreed to indemnify its officers and directors against certain liabilities,
including liabilities arising out of the offering made by this registration
statement.

     Celgene maintains a standard form of officers' and directors' liability
insurance policy which provides coverage to the officers and directors of
Celgene for certain liabilities, including certain liabilities which may arise
out of the registration statement.


ITEM 21. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES


(A) EXHIBITS

The following exhibits are filed herewith or incorporated herein by reference.





<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                            DESCRIPTION
--------                                         ------------
<S>      <C>
    2.1  Agreement and Plan of Merger, dated as of June 29, 2000, among Celgene Corporation,
         Celgene Acquisition Corp. and Signal Pharmaceuticals, Inc. (incorporated by reference to
         Appendix A to the proxy statement/prospectus filed as part of this registration statement).
    2.2  Form of Voting and Proxy  Agreement  among Celgene  Corporation and the
         Shareholders listed on Schedule A thereto (incorporated by reference to
         Exhibit  A-1 to Appendix A to the proxy  statement/prospectus  filed as
         part of this registration statement).
    2.3  Form of Option Agreement between Celgene Corporation and Signal Pharmaceuticals, Inc.
         (incorporated by reference to Exhibit A-2 to Appendix A to the proxy
         statement/prospectus filed as part of this registration statement).
    2.4  Form of Affiliate Agreement of affiliates of Signal Pharmaceuticals, Inc. (incorporated by
         reference to Exhibit C to Appendix A to the proxy statement/prospectus filed as part of
         this registration statement).
    5.1  Form of Opinion of Proskauer Rose LLP,  counsel to Celgene  Corporation,  as to
         the legality of the Celgene common stock being registered hereby.
    8.1  Form of Opinion of Proskauer Rose LLP, counsel to Celgene  Corporation,
         regarding tax matters.
    8.2  Form Of Opinion of Cooley Godward LLP, counsel to Signal Pharmaceuticals,
         Inc. regarding tax matters.
  *10.1  *Form of Employment Agreement with Alan Lewis.
   23.1  Consent of KPMG LLP.
   23.2 Consent of Proskauer Rose LLP (incorporated by reference to Exhibits 5.1
and 8.1).
</TABLE>

                                      II-1
<PAGE>


<TABLE>
<CAPTION>
23.3      Consent of Pennie & Edmonds LLP.
<S>       <C>
23.4      Consent of Kleinfeld, Kaplan & Becker.
23.5      Consent of Mathew, Collins, Shepherd & Gould, P.A.
23.6      Consent of Cooley Godward LLP (incorporated by reference to Exhibit 8.2).
23.7      Consent of FleetBoston Robertson Stephens Inc.
23.8      Consent of Ernst & Young LLP, Independent Auditors
24.1      Power of Attorney (included in Signature Pages).
99.1      Form of Proxy to be used in connection with special meeting of shareholders of Signal
          Pharmaceuticals, Inc.
</TABLE>

----------
* To be filed by amendment.


(B) FINANCIAL STATEMENT SCHEDULES

All schedules have been omitted as the required information is presented in the
consolidated financial statements or related notes incorporated by reference in
the proxy statement/prospectus or are not applicable.


(C) REPORTS, OPINIONS AND APPRAISALS

Opinion of FleetBoston Robertson Stephens Inc. (incorporated by reference to
Appendix C to the proxy statement/prospectus filed as part of this registration
statement).


ITEM 22. UNDERTAKINGS

(a) The undersigned registrant hereby undertakes:

   (1)  To file, during any period in which offers or sales are being made, a
        post-effective amendment to this registration statement:

       (i)  To include any prospectus required by section 10(a)(3) of the
            Securities Act of 1933;

       (ii) To reflect in the prospectus any facts or events arising after the
            effective date of the registration statement (or the most recent
            post-effective amendment thereof) which, individually or in the
            aggregate, represent a fundamental change in the information set
            forth in the registration statement. Notwithstanding the foregoing,
            any increase or decrease in volume of securities offered (if the
            total dollar value of securities offered would not exceed that which
            was registered) and any deviation from the low or high and of the
            estimated maximum offering range may be reflected in the form of
            prospectus filed with the Commission pursuant to Rule 424(b) if, in
            the aggregate, the changes in volume and price represent no more
            than 20 percent change in the maximum aggregate offering price set
            forth in the "Calculation of Registration Fee" table in the
            effective Registration Statement; and

      (iii) To include any material information with respect to the plan of
            distribution not previously disclosed in the registration statement
            or any material change to such information in the registration
            statement.

   provided, however, that paragraphs (i) and (ii) do not apply if the
   registration statement is on Form S-3, Form S-8 or Form F-3, and the
   information required to be included in a post-effective amendment by those
   paragraphs is contained in periodic reports filed with or furnished to the
   Commission by the registrant pursuant to Section 13 or 15(d) of the
   Securities Exchange Act of 1934 that are incorporated by reference in the
   registration statement.


                                      II-2
<PAGE>

   (2)  That, for the purpose of determining any liability under the Securities
        Act of 1933, each such post-effective amendment shall be deemed to be a
        new registration statement relating to the securities offered therein,
        and the offering of such securities at that time shall be deemed to be
        the initial bona fide offering thereof.

   (3)  To remove from registration by means of a post-effective amendment any
        of the securities being registered which remain unsold at the
        termination of the offering.

(b)  The undersigned registrant hereby undertakes that, for purposes of
     determining any liability under the Securities Act of 1933, each filing of
     the registrant's annual report pursuant to Section 13(a) or 15(d) of the
     Securities Exchange Act of 1934 (and, where applicable, each filing of an
     employee benefit plan's annual report pursuant to Section 15(d) of the
     Securities Exchange Act of 1934) that is incorporated by reference in the
     registration statement shall be deemed to be a new registration statement
     relating to the securities offered therein, and the offering of such
     securities at that time shall be deemed to be the initial bona fide
     offering thereof.

(c)  The undersigned registrant hereby undertakes as follows: that prior to any
     public reoffering of the securities registered hereunder through use of a
     prospectus which is a part of the registration statement, by any person or
     party who is deemed to be an underwriter within the meaning of Rule 145(c),
     the issuer undertakes that such reoffering prospectus will contain the
     information called for by the applicable registration form with respect to
     reofferings by persons who may be deemed underwriters, in addition to the
     information called for by the other items of the applicable form.

(d)  The registrant undertakes that every prospectus: (i) that is filed pursuant
     to paragraph (c) immediately preceding or (ii) that purports to meet the
     requirements of Section 10(a)(3) of the Act and is used in connection with
     an offering of securities subject to Rule 415, will be filed as a part of
     an amendment to the registration statement and will not be used until such
     amendment is effective, and that, for purposes of determining any liability
     under the Securities Act of 1933, each such post-effective amendment shall
     be deemed to be a new registration statement relating to the securities
     offered therein, and the offering of such securities at that time shall be
     deemed to be the initial bona fide offering thereof.

(e)  Insofar as indemnification for liabilities arising under the Securities Act
     of 1933 may be permitted to directors, officers and controlling persons of
     the registrant pursuant to the foregoing provisions, or otherwise, the
     registrant has been advised that in the opinion of the Securities and
     Exchange Commission such indemnification is against public policy as
     expressed in the Act and is, therefore, unenforceable. In the event that
     such a claim for indemnification against such liabilities (other than the
     payment by the registrant of expenses incurred or paid by a director,
     officer or controlling person of the registrant in the successful defense
     of any action, suit or proceeding) is asserted by such director, officer or
     controlling person in connection with the securities being registered, the
     registrant will, unless in the opinion of its counsel the matter has been
     settled by controlling precedent, submit to a court of appropriate
     jurisdiction the question whether such indemnification by it is against
     public policy as expressed in the Act and will be governed by the final
     adjudication of such issue.

(f)  The undersigned registrant hereby undertakes to respond to requests for
     information that is incorporated by reference into the prospectus pursuant
     to Items 4, 10(b), 11 or 13 of this form, within one business day of
     receipt of such request, and to send the incorporated documents by first
     class mail or other equally prompt means. This includes information
     contained in documents filed subsequent to the effective date of the
     registration statement through the date of responding to the request.

(g)  The undersigned registrant hereby undertakes to supply by means of a
     post-effective amendment all information concerning a transaction, and the
     company being acquired involved therein, that was not the subject of and
     included in the registration statement when it became effective.


                                      II-3
<PAGE>

                        SIGNATURES AND POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENT, that each person or entity whose signature
appears below constitutes and appoints John W. Jackson, Sol J. Barer and Robert
J. Hugin, and each of them, its true and lawful attorneys-in-fact and agents,
with full power of substitution and resubstitution, for it and in its name,
place and stead, in any and all capacities, to sign any and all amendments to
this registration statement on Form S-4 and to file the same, with all exhibits
thereto, and other documents in connection therewith, with the Securities and
Exchange Commission, granting unto said attorneys-in-fact and agents, and each
of them, full power and authority to do and perform each and every act and thing
requisite and necessary to be done, as fully to all intents and purposes as it
might or could do in person, hereby ratifying and confirming all that said
attorneys-in-fact and agents or any of them, or their or his substitute or
substitutes may lawfully do or cause to be done by virtue thereof.

Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-4 and has duly caused this registration
statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the city of Warren, State of New Jersey on July 26, 2000.


                                        CELGENE CORPORATION


                                        By: /s/ John W. Jackson
                                           ------------------------------------

                                            John W. Jackson
                                            Chairman of the Board
                                            and Chief Executive Officer

Pursuant to the requirements of the Securities Act, this registration  statement
has been signed  below by the  persons  whose  signatures  appear  below,  which
persons have signed such registration statement in the capacities indicated:





<TABLE>
<CAPTION>
             SIGNATURE                               TITLE                       DATE
<S>                                <C>                                      <C>
        /s/ John W. Jackson        Chairman of the Board and Chief          July 26, 2000
 -------------------------------
                                   Executive Officer (Principal Executive
          John W. Jackson
                                   Officer)
          /s/ Sol J. Barer         President, Chief Operating Officer and   July 26, 2000
 -------------------------------
                                    Director
            Sol J. Barer
        /s/ Robert J. Hugin        Chief Financial Officer (Principal       July 26, 2000
 -------------------------------
                                   Accounting and Financial Officer)
          Robert J. Hugin
         /s/ Jack L. Bowman        Director                                 July 26, 2000
 -------------------------------
           Jack L. Bowman
         /s/ Frank T. Cary         Director                                 July 26, 2000
 -------------------------------
           Frank T. Cary
          /s/ Gilla Kaplan         Director                                 July 26, 2000
 -------------------------------
            Gilla Kaplan
       /s/ Arthur Hull Hayes, Jr.  Director                                 July 26, 2000
 -------------------------------
         Arthur Hull Hayes, Jr.

        /s/ Richard C.E. Morgan    Director                                 July 26, 2000
 -------------------------------
        Richard C.E. Morgan
         /s/ Walter L. Robb        Director                                 July 26, 2000
 -------------------------------
           Walter L. Robb
        /s/ Lee J. Schroeder       Director                                 July 26, 2000
 -------------------------------
  Lee J. Schroeder
</TABLE>

                                      II-4
<PAGE>

                                  EXHIBIT INDEX



<TABLE>
<CAPTION>
EXHIBIT
NUMBER                                            DESCRIPTION
--------                                         -------------
<S>      <C>
  2.1    Agreement and Plan of Merger, dated as of June 29, 2000, among Celgene Corporation,
         Celgene Acquisition Corp. and Signal Pharmaceuticals, Inc. (incorporated by reference to
         Appendix A to the proxy statement/prospectus filed as part of this registration statement).
  2.2    Form of Voting and Proxy  Agreement  among Celgene  Corporation and the
         Shareholders listed on Schedule A thereto (incorporated by reference to
         Exhibit  A-1 to Appendix A to the proxy  statement/prospectus  filed as
         part of this registration statement).
  2.3    Form of Option Agreement between Celgene Corporation and Signal Pharmaceuticals, Inc.
         (incorporated by reference to Exhibit A-2 to Appendix A to the proxy
         statement/prospectus filed as part of this registration statement).
  2.4    Form of Affiliate Agreement of affiliates of Signal Pharmaceuticals, Inc. (incorporated by
         reference to Exhibit C to Appendix A to the proxy statement/prospectus filed as part of
         this registration statement).
  5.1    Form of Opinion of Proskauer Rose LLP,  counsel to Celgene  Corporation,  as to
         the legality of the Celgene common stock being registered hereby.
  8.1    Form of Opinion of Proskauer Rose LLP, counsel to Celgene  Corporation,
         regarding tax matters.
  8.2    Form Of Opinion of Cooley Godward LLP, counsel to Signal Pharmaceuticals,
         Inc. regarding tax matters.

*10.1    Form of Employment Agreement with Alan Lewis.
 23.1    Consent of KPMG LLP.
 23.2    Consent of Proskauer Rose LLP (incorporated by reference to Exhibit 5.1 and 8.1).
 23.3    Consent of Pennie & Edmonds LLP.
 23.4    Consent of Kleinfeld, Kaplan & Becker.
 23.5    Consent of Mathew, Collins, Shepherd & Gould, P.A.
 23.6    Consent of Cooley Godward LLP (incorporated by reference to Exhibit 8.2).
 23.7    Consent of FleetBoston Robertson Stephens Inc.
 23.8    Consent of Ernst & Young LLP, Independent Auditors
 24.1    Power of Attorney (included in Signature Pages).
 99.1    Form  of  Proxy  to be used  in  connection  with  special  meeting  of
         shareholders of Signal Pharmaceuticals, Inc.
</TABLE>

----------
* To be filed by amendment.


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