SOMATIX THERAPY CORPORATION
SC 13D, 1997-01-22
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>   1
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13D


                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                               (AMENDMENT NO. __)*


                               CELL GENESYS, INC.
- --------------------------------------------------------------------------------
                                (NAME OF ISSUER)


                     Common Stock, Par Value $.001 Per Share
- --------------------------------------------------------------------------------
                         (TITLE OF CLASS OF SECURITIES)


                                   0001509211
- --------------------------------------------------------------------------------
                                 (CUSIP NUMBER)

                           J. Stephan Dolezalek, Esq.
                         Brobeck, Phleger & Harrison LLP
                              Two Embarcadero Place
                                 2200 Geng Road
                        Palo Alto, California 94303-0913
                                 (415) 424-0160
- --------------------------------------------------------------------------------
          (Name, Address and Telephone Number of Person Authorized to
                      Receive Notices and Communications)

                                January 12, 1997
                    ---------------------------------------
             (DATE OF EVENT WHICH REQUIRES FILING OF THIS STATEMENT)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(b)(3) or (4), check the following box. / /

NOTE: Six copies of this statement, including all exhibits, should be filed with
the Commission. See Rule 13d-1(a) for other parties to whom copies are to be
sent.

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).


<PAGE>   2
- ----------------------                                        
CUSIP NO.   0001509211                 13D                    
- ----------------------                                        

- --------------------------------------------------------------------------------
1          NAME OF REPORTING PERSON
           S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Somatix Therapy Corporation
- --------------------------------------------------------------------------------
2          CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*             (a) / /
                                                                         (b) / /

- --------------------------------------------------------------------------------
3          SEC USE ONLY


- --------------------------------------------------------------------------------
4          SOURCE OF FUNDS*
           00 (See Item 3)
- --------------------------------------------------------------------------------
5          CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO 
           ITEMS 2(d) OR 2(e)                                                / /

- --------------------------------------------------------------------------------
6          CITIZENSHIP OR PLACE OF ORGANIZATION

           Delaware
- --------------------------------------------------------------------------------
 NUMBER OF    7          SOLE VOTING POWER
  SHARES                       
BENEFICIALLY             3,286,703 shares **
  OWNED BY    ------------------------------------------------------------------
   EACH       8          SHARED VOTING POWER
REPORTING
  PERSON                 0 shares
   WITH       ------------------------------------------------------------------
              9          SOLE DISPOSITIVE POWER
              
                         3,286,703 shares **
              ------------------------------------------------------------------
              10         SHARED DISPOSITIVE POWER
                 
                         0 shares
- --------------------------------------------------------------------------------
11         AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           3,286,703 shares**
- --------------------------------------------------------------------------------
12         CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN 
           SHARES*                                                           / /

- --------------------------------------------------------------------------------
13         PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

           19.9%
- --------------------------------------------------------------------------------
14         TYPE OF REPORTING PERSON*

           CO
- --------------------------------------------------------------------------------

                      *SEE INSTRUCTIONS BEFORE FILLING OUT!
          INCLUDE BOTH SIDES OF THE COVER PAGE, RESPONSES TO ITEMS 1-7
      (INCLUDING EXHIBITS) OF THE SCHEDULE, AND THE SIGNATURE ATTESTATION.


**       Neither the filing of this Schedule 13D nor any of its contents shall
         be deemed to constitute an admission by Somatix Therapy Corporation
         that it is the beneficial owner of any of the shares of Issuer Common
         Stock referred to herein for purposes of Section 13(d) of the
         Securities Exchange Act of 1934, as amended, or for any other purpose,
         and such beneficial ownership is expressly disclaimed.


<PAGE>   3
CUSIP NO.:   0001509211                13D                    



ITEM 1.  SECURITY AND ISSUER.

         This Statement on Schedule 13D (this "Schedule 13D") relates to shares
of common stock, $.001 par value par share (the "Issuer Common Stock"), of Cell
Genesys, Inc., a Delaware corporation (the "Issuer"). The principal executive
offices of the Issuer are located at 322 Lakeside Drive, Foster City, California
94404.


ITEM 2.  IDENTITY AND BACKGROUND.

         (a)-(c), (f) This Schedule 13D is being filed on behalf of Somatix
Therapy Corporation, a Delaware corporation ("STC"). Neither the filing of this
Schedule 13D nor the information contained herein shall be deemed to constitute
an affirmation by STC that it is the beneficial owner of the Issuer Common Stock
referred to herein for purposes of Section 13(d) of the Securities Exchange Act
of 1934, as amended (the "Exchange Act") or for any other purpose, and such
beneficial ownership is expressly disclaimed.

         STC is principally engaged in the field of gene therapy. STC's mission
is to research, develop and commercialize proprietary processes for the genetic
modification of cells and their use in the treatment of human disease. STC's
principal executive offices are located at 950 Marina Village Parkway, Suite
100, Alameda, California 94501.

         The name, citizenship, residence or business address and principal
occupation or employment (and the name, principal business and address of any
corporation or other organization in which such employment is conducted) of each
director and executive officer of STC is set forth in Schedule A hereto.

         (d)-(e) Neither STC nor, to the best of STC's knowledge, any of the
directors or executive officers of STC has, during the past five years: (i) been
convicted in a criminal proceeding (excluding traffic violations or similar
misdemeanors); or (ii) been a party to a civil proceeding of a judicial or
administrative body of competent jurisdiction and as a result of such proceeding
was or is subject to a judgment, decree or final order enjoining future
violations of, or prohibiting or mandating activities subject to, federal or
state securities laws or finding any violation with respect to such laws.

         (f)      Not Applicable.


ITEM 3.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

         This statement relates to 3,286,703 shares of Issuer Common Stock
subject to the Stock Option Agreement, dated as of January 12, 1997 (the "Issuer
Stock Option Agreement"), between the Issuer and STC, pursuant to which the
Issuer granted to STC an option (the "STC Option") to purchase up to 3,286,703
newly-issued shares of Issuer Common Stock at an exercise price per share equal
to $9.12. No cash consideration was


<PAGE>   4
CUSIP NO.:   0001509211                13D                    


paid by STC to the Issuer for the STC Option. If STC were to exercise the STC
Option in full, the total amount of funds required would be $29,974,731. STC
anticipates that such funds would be obtained from its available capital,
including the proceeds of borrowings as to which no arrangements have been made.

         As a condition to the willingness of STC to enter into (i) the
Agreement and Plan of Merger and Reorganization, dated as of January 12, 1997
(the "Merger Agreement"), among STC, the Issuer and S Merger Corp., a direct
wholly owned subsidiary of the Issuer ("Merger Sub"), providing for, among other
things, the merger (the "Merger") of Merger Sub with and into STC, whereupon the
separate corporate existence of Merger Sub shall cease and STC shall continue as
the surviving corporation of the Merger and a wholly-owned subsidiary of the
Issuer, and (ii) the Stock Option Agreement, dated as of January 12, 1997 (the
"STC Stock Option Agreement"), between STC, as grantor, and the Issuer, as
grantee, pursuant to which STC granted to the Issuer an option (the "Issuer
Option") to purchase up to 5,441,480 shares of common stock of STC at an
exercise price per share equal to $3.51, representing approximately 19.9% of the
shares of such common stock issued and outstanding on the date of grant, STC
required that the Issuer agree to, and in order to induce STC to enter into the
Merger Agreement and the STC Stock Option Agreement, the Issuer agreed to,
execute the Issuer Stock Option Agreement and grant the STC Option to STC.

         The obligations of the parties under the Merger Agreement to effect the
Merger are subject to certain conditions, including the approval of the Merger
and the Merger Agreement by the stockholders of the Issuer and STC. Prior to the
effective time of the Merger, the Issuer or STC may terminate the Merger
Agreement under certain circumstances, in each case as set forth in Section 9.01
of the Merger Agreement. Section 9.05 of the Merger Agreement sets forth certain
circumstances under which termination of the Merger Agreement by the Issuer or
STC shall obligate the Issuer or STC, as the case may be, to pay to the other
party certain amounts as specified in Section 9.05 of the Merger Agreement.

         In accordance with the terms and subject to the conditions set forth in
the Issuer Stock Option Agreement, the STC Option may be exercised by STC, in
whole or in part, at any time or from time to time after the occurrence of an
Exercise Event (as defined below) and prior to the Termination Date (as defined
below). For purposes of the Issuer Stock Option Agreement, (x) an "Exercise
Event" shall occur upon the occurrence of any event or circumstance which
obligates the Issuer, or, in the case of Section 9.05(c)(ii) of the Merger
Agreement, may obligate the Issuer in the event a Competing Transaction (as
defined in the Merger Agreement) is consummated within the 12-month period
referred to in the Merger Agreement, to pay to STC any amount specified pursuant
to Section 9.05 of the Merger Agreement, and (y) the "Termination Date" shall
occur upon the first to occur of any of (i) the Effective Time of the Merger,
(ii) the termination of the Issuer Stock Option Agreement in accordance with its
terms, or (iii) the date which is 90 days after the occurrence of an Exercise
Event.


<PAGE>   5
         The Issuer Stock Option Agreement provides that, in the event STC
wishes to exercise the STC Option, it must send a written notice to the Issuer
specifying (i)(A) the total number of shares of Issuer Common Stock STC wishes
to purchase and the denominations of the certificate or certificates evidencing
such shares of Issuer Common Stock which STC wishes to receive or (B) the total
number of shares of Issuer Common Stock STC wishes to receive cash payment with
respect to, and (ii) a date and place for the closing of such purchase or
payment. Upon receipt of such an exercise notice, the Issuer will be obligated
to (i) deliver to STC a certificate or certificates evidencing the number of
shares of Issuer Common Stock specified in such exercise notice or (ii) pay to
STC an amount in cash equal to (A) the excess, if any, over the exercise price
for the shares of Issuer Common Stock of the higher of (1) if applicable, the
highest price per share of Issuer Common Stock paid by any person in a Competing
Transaction (as defined in the Merger Agreement) and (2) the closing price of
the shares of Issuer Common Stock on the Nasdaq National Market on the last
trading day immediately prior to the date of the applicable exercise notice,
multiplied by (B) the number of shares of Issuer Common Stock specified in such
exercise notice. Notwithstanding the foregoing, the Issuer may, by written
notice to STC within three business days after receipt of an exercise notice
under the Issuer Stock Option Agreement with respect to the purchase of shares
of Issuer Common Stock as described in clause (i) of the preceding sentence,
elect to pay to STC within 10 business days following receipt of such exercise
notice an amount in cash calculated as described in clause (ii) of the preceding
sentence. Furthermore, if at the time a cash payment elected by STC upon
exercise of the STC Option is due, the Issuer has not consummated a Competing
Transaction, the Issuer may elect to make such payment in cash or in shares of
Issuer Common Stock valued at the closing price of shares of Issuer Common Stock
on the Nasdaq National Market on the business day prior to such payment.

         The Issuer Stock Option Agreement provides for customary anti-dilution
adjustments in the event of any change in shares of Issuer Common Stock or in
the number of outstanding shares of Issuer Common Stock by reason of a stock
dividend, split-up, recapitalization, combination, exchange of shares or similar
transaction or any other change in the corporate or capital structure of the
Issuer. The Issuer Stock Option Agreement further provides that, in the event
that the Issuer enters into a merger agreement pursuant to which it will not be
the surviving corporation or pursuant to which a change of control of the Issuer
will occur or an agreement to sell or otherwise transfer all or substantially
all of its assets to any person, other than STC or any of its subsidiaries, then
proper provision must be made in the agreements governing such transaction so
that STC will receive upon exercise of the STC Option the number and class of
shares or other securities or property that STC would have received in respect
of shares of Issuer Common Stock if the STC Option had been exercised
immediately prior to such transaction, or the record date therefor, as
applicable, and elected to the fullest extent it would have been permitted to
elect to receive such securities, cash or other property.


<PAGE>   6
         The Issuer Stock Option Agreement contains certain customary
representations and warranties on the part of STC and the Issuer, including
covenants on the part of the Issuer with respect to the listing of the shares of
Issuer Common Stock for quotation on the Nasdaq National Market and the
registration of the shares of Issuer Common Stock under the Securities Act and
any applicable state securities laws.

        The Issuer Stock Option Agreement will terminate by its terms on
February 12, 1998.
<PAGE>   7
CUSIP NO.:   0001509211                 13D                   


                  The preceding summary of certain provisions of the Merger
Agreement and the Issuer Stock Option Agreement is not intended to be complete
and is qualified in its entirety by reference to the full text of such
agreements, copies of which are filed as Exhibits 1 and 2 hereto, and which are
incorporated herein by reference.


ITEM 4.  PURPOSE OF TRANSACTION.

         As stated above, the STC Option was granted by the Issuer to STC as an
inducement to STC to enter into the Merger Agreement and the STC Stock Option
Agreement.

         Other than as described above, STC has no plans or proposals that
relate to or would result in any of the actions described in subparagraphs (a)
through (j) of Item 4 of Schedule 13D (although subject to the provisions of the
Merger Agreement STC reserves the right to develop such plans).


ITEM 5.  INTEREST IN SECURITIES OF THE ISSUER.

         (a) Under the definition of "beneficial ownership" as set forth in Rule
13d-3 under the Securities Exchange Act of 1934, as amended, STC may be deemed
to be the beneficial owner of the 3,286,703 shares of Issuer Common Stock
issuable upon exercise of the STC Option. Such 3,286,703 shares of Issuer Common
Stock constitute approximately 19.9% of the number of shares of Issuer Common
Stock issued and outstanding as of January 10, 1997, and STC's percentage
interest in the Issuer Common Stock would be approximately 16.6% after the
exercise of the STC Option in full.(1)

         The shares of Issuer Common Stock described herein are subject to the
STC Option, which is not currently exercisable. STC does not own any shares of
Issuer Common Stock other than those shares which may be acquired upon exercise
of the STC Option.

         Neither the filing of this Schedule 13D nor any of its contents shall
be deemed to constitute an admission that STC is the beneficial owner of the
Issuer Common Stock which may be acquired upon exercise of the STC Option for
purposes of Section 13(d) of the Exchange Act or for any other purpose, and such
beneficial ownership is expressly disclaimed.

         (b) If STC exercises the STC Option, STC expects to have the sole power
to vote or direct the vote of, and sole power to dispose or direct the
disposition of, any shares of Issuer Common Stock which STC may acquire upon
such exercise.

- --------
         (1) Based on 16,516,099 shares of Issuer Common Stock outstanding as of
January 10, 1997, according to the representation of the Issuer contained in
Section 5.03 of the Merger Agreement.


<PAGE>   8
CUSIP NO.:   0001509211                13D                    



         (c) Except as set forth in this Schedule 13D, neither STC, nor, to the
best knowledge of STC, any person named in Schedule A hereto, has effected any
transaction in the Issuer Common Stock during the past 60 days.

         (d) Not applicable.

         (e) Not applicable.


ITEM 6.  CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT 
         TO SECURITIES OF THE ISSUER.

         Except as set forth in this Schedule 13D, to the best knowledge of STC,
there are no other contracts, arrangements, understandings or relationships
(legal or otherwise) among the persons named in Item 2 and between such persons
and any person with respect to any securities of the Issuer, including but not
limited to, transfer or voting of any of the securities of the Issuer, joint
ventures, loan or option arrangements, puts or calls, guarantees of profits,
division of profits or loss, or the giving or withholding of proxies, or a
pledge or contingency the occurrence of which would give another person voting
power or investment power over the securities of the Issuer.


ITEM 7.  MATERIALS TO BE FILED AS EXHIBITS.

         The following documents are filed as exhibits:


         1.       Agreement and Plan of Merger and Reorganization, dated January
                  12, 1997, among Cell Genesys, Inc., S Merger Corp., and
                  Somatix Therapy Corporation.

         2.       Stock Option Agreement, dated as of January 12, 1997, between
                  Cell Genesys, Inc. and Somatix Therapy Corporation.


<PAGE>   9
CUSIP NO.:   0001509211                 13D                   



                                    SIGNATURE


         After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this Statement is true, complete and
correct.


Dated:   January 22, 1997

                                              SOMATIX THERAPY CORPORATION
                                              
                                              
                                              
                                              By: /s/ Edward O. Lanphier
                                                 -------------------------------
                                              Edward O. Lanphier
                                              Executive Vice President and Chief
                                              Financial Officer                 
                           
<PAGE>   10
CUSIP NO.:   0001509211                13D                    


                                   SCHEDULE A

         Set forth below are the names, present principal occupations and
business address (if other than STC) of each of the directors and executive
officers of STC. Except as otherwise indicated, the principal business address
of each such person is 950 Marina Village Parkway, Suite 100, Alameda,
California 94501. Except as otherwise indicated, all of the persons listed below
are United States citizens.


DIRECTORS:
- ----------

<TABLE>
<CAPTION>
                                                    PRINCIPAL OCCUPATION
NAME                                                AND BUSINESS ADDRESS
- ----                                                --------------------
<S>                                 <C>
David W. Carter                     Chairman of the Board, President and Chief Executive
                                    Officer of STC


Karen Davis, Ph.D.                  President, The Commonwealth Fund
                                    One East 75th Street
                                    New York, NY  10021-2692


Michael R. Eisenson                 President and Chief Executive Officer, Harvard Private
                                    Capital Group, Inc.
                                    600 Atlantic Avenue
                                    Boston, MA  02210-2203


Fred H. Gage, Ph.D                  Professor of Neuroscience, The Salk Institute
                                    University of California at San Diego
                                    Department of Neurosciences
                                    9500 Gilman Drive
                                    La Jolla, CA  92093-0624


John T. Potts, Jr., M.D.            Director of Research, Massachusetts General Hospital
                                    and Jackson Distinguished Professor of Medicine
                                    Massachusetts General Hospital
                                    32 Fruit Street, GRB 740
                                    Boston, MA  02114-2698
</TABLE>


<PAGE>   11
CUSIP NO.:   0001509211                 13D                   


<TABLE>
<S>                                 <C>
Leon E. Rosenberg, M.D.             President, Bristol-Myers Squibb Pharmaceutical
                                    Research Institute
                                    Bristol-Myers Squibb Company
                                    Route 206 and Province Line Road
                                    Princeton, NJ  08543-4000


Thomas E. Shenk, Ph.D.              Howard Hughes Professor of Molecular Biology,
                                    Princeton University
                                    Princeton, NJ  08544-1014


Inder M. Verma, Ph.D.               Chairman of the Faculty and Academic Counsel, The
                                    Salk Institute and Co-Director of the Laboratory of
                                    Genetics, The Salk Institute
                                    10010 North Torrey Pines Road
                                    La Jolla, CA  92037


Samuel D. Waksal, Ph.D.             President, Chief Executive Officer, Imclone Systems,
                                    Incorporated
                                    180 Varick Street
                                    Seventh Floor
                                    New York, NY  10014
</TABLE>



EXECUTIVE OFFICERS:

<TABLE>
<CAPTION>
                                                    PRINCIPAL OCCUPATION
NAME                                                AND BUSINESS ADDRESS
- ----                                                --------------------
<S>                                <C>
David W. Carter                    Chairman of the Board, President and Chief Executive
                                   Officer of STC


Edward O. Lanphier II              Executive Vice President, Commercial Development and
                                   Chief Financial Officer of STC



Lawrence K. Cohen, Ph.D.           Vice President Research of STC
</TABLE>


<PAGE>   12
CUSIP NO.:   0001509211                13D                   


<TABLE>
<S>                                <C>
Joseph A. Rokovich, Ph.D.           Vice President, Regulatory, Clinical Operations, QA/QC
                                    and Project Management of STC
</TABLE>


<PAGE>   13
CUSIP NO.:   0001509211                13D                 


                                  EXHIBIT INDEX


1.       Agreement and Plan of Merger and Reorganization, dated January 12,
         1997, among Cell Genesys, Inc., S Merger Corp., and Somatix Therapy
         Corporation.

2.       Stock Option Agreement, dated as of January 12, 1997, between Cell
         Genesys, Inc. and Somatix Therapy Corporation.


<PAGE>   14
                                                                      EXHIBIT 1

                                                                  CONFORMED COPY












                 AGREEMENT AND PLAN OF MERGER AND REORGANIZATION



                                      among


                               CELL GENESYS, INC.

                                 S MERGER CORP.

                                       and

                           SOMATIX THERAPY CORPORATION




                          Dated as of January 12, 1997


<PAGE>   15
                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                               Page
                                                                                               ----
<S>            <C>                                                                             <C>
                                    ARTICLE I

                                   DEFINITIONS
SECTION 1.01.  Certain Defined Terms..........................................................   2
                                                                                               
                                                                                               
                                   ARTICLE II
                                                                                               
                                   THE MERGER
                                                                                               
SECTION 2.01.  The Merger.....................................................................  12
SECTION 2.02.  Closing........................................................................  12
SECTION 2.03.  Effective Time.................................................................  13
SECTION 2.04.  Effect of the Merger...........................................................  13
SECTION 2.05.  Certificate of Incorporation; By-laws; Directors and Officers                   
                  of Surviving Corporation....................................................  13
                                                                                               
                                                                                               
                                   ARTICLE III
                                                                                               
               CONVERSION OF SECURITIES; EXCHANGE OF CERTIFICATES
                                                                                               
SECTION 3.01.  Conversion of Securities.......................................................  14
SECTION 3.02.  Exchange of Shares Other than Treasury Shares..................................  15
SECTION 3.03.  Stock Transfer Books...........................................................  16
SECTION 3.04.  No Fractional Share Certificates...............................................  16
SECTION 3.05.  Options and Warrants to Purchase STC Common Stock..............................  18
SECTION 3.06.  Certain Adjustments............................................................  19
                                                                                               
                                                                                               
                                   ARTICLE IV
                                                                                               
                      REPRESENTATIONS AND WARRANTIES OF STC
                                                                                               
SECTION 4.01.  Organization and Qualification; Subsidiaries...................................  19
SECTION 4.02.  Certificate of Incorporation and By-laws.......................................  19
SECTION 4.03.  Capitalization.................................................................  20
</TABLE>


                                        i

<PAGE>   16
<TABLE>
<CAPTION>
                                                                                               Page
                                                                                               ----
<S>            <C>                                                                             <C>
SECTION 4.04.  Authority Relative to This Agreement and the STC Stock
                  Option Agreement............................................................  20
SECTION 4.05.  No Conflict; Required Filings and Consents.....................................  21
SECTION 4.06.  Permits; Compliance with Laws..................................................  22
SECTION 4.07.  SEC Filings; Financial Statements; Projected Cash Balances;                     
                  Operating Budget............................................................  23
SECTION 4.08.  Absence of Certain Changes or Events...........................................  24
SECTION 4.09.  Employee Benefit Plans; Labor Matters..........................................  25
SECTION 4.10.  Tax Matters....................................................................  26
SECTION 4.11.  Contracts; Debt Instruments....................................................  26
SECTION 4.12.  Litigation.....................................................................  27
SECTION 4.13.  Environmental Matters..........................................................  27
SECTION 4.14.  Intellectual Property..........................................................  27
SECTION 4.15.  Taxes..........................................................................  28
SECTION 4.16.  Opinion of Financial Advisor...................................................  28
SECTION 4.17.  Brokers........................................................................  28
SECTION 4.18.  Certain Interests..............................................................  28
                                                                                               
                                                                                               
                                    ARTICLE V
                                                                                               
               REPRESENTATIONS AND WARRANTIES OF CGI AND MERGER SUB
                                                                                               
SECTION 5.01.  Organization and Qualification; Subsidiaries...................................  29
SECTION 5.02.  Certificate of Incorporation and By-laws.......................................  30
SECTION 5.03.  Capitalization.................................................................  30
SECTION 5.04.  Authority Relative to This Agreement and the CGI Stock                          
                  Option Agreement............................................................  31
SECTION 5.05.  No Conflict; Required Filings and Consents.....................................  31
SECTION 5.06.  Permits; Compliance with Laws..................................................  32
SECTION 5.07.  SEC Filings; Financial Statements..............................................  33
SECTION 5.08.  Absence of Certain Changes or Events...........................................  34
SECTION 5.09.  Employee Benefit Plans; Labor Matters..........................................  34
SECTION 5.10.  Tax Matters....................................................................  36
SECTION 5.11.  Contracts; Debt Instruments....................................................  36
SECTION 5.12.  Litigation.....................................................................  36
SECTION 5.13.  Environmental Matters..........................................................  37
SECTION 5.14.  Intellectual Property..........................................................  37
SECTION 5.15.  Taxes..........................................................................  38
SECTION 5.16.  Opinion of Financial Advisor...................................................  38
SECTION 5.17.  Brokers........................................................................  38
</TABLE>


                                       ii

<PAGE>   17
<TABLE>
<CAPTION>
                                                                                               Page
                                                                                               ----
<S>            <C>                                                                             <C>
SECTION 5.18.  Certain Interests..............................................................  38
                                                                                               
                                                                                               
                                   ARTICLE VI                                                  
                                                                                               
                                    COVENANTS                                                  
                                                                                               
SECTION 6.01.  Conduct of Business by STC Pending the Closing.................................  39
SECTION 6.02.  Conduct of Business by CGI Pending the Closing.................................  41
SECTION 6.03.  Cooperation; Steering Committee................................................  43
SECTION 6.04.  Notices of Certain Events......................................................  44
SECTION 6.05.  Access to Information; Confidentiality.........................................  44
SECTION 6.06.  No Solicitation of Transactions................................................  44
SECTION 6.07.  Plan of Reorganization.........................................................  45
SECTION 6.08.  Subsequent Financial Statements................................................  46
SECTION 6.09.  Control of Operations..........................................................  46
SECTION 6.10.  Further Action; Consents; Filings..............................................  46
                                                                                               
                                                                                               
                                   ARTICLE VII                                                 
                                                                                               
                              ADDITIONAL AGREEMENTS                                            
                                                                                               
SECTION 7.01.  Registration Statement; Joint Proxy Statement..................................  47
SECTION 7.02.  Stockholders' Meetings.........................................................  49
SECTION 7.03.  Affiliates.....................................................................  49
SECTION 7.04.  Directors' and Officers' Indemnification and Insurance.........................  50
SECTION 7.05.  No Shelf Registration..........................................................  51
SECTION 7.06.  Public Announcements...........................................................  51
SECTION 7.07.  Officers and Directors of CGI..................................................  51
SECTION 7.08.  NMS Listing....................................................................  52
SECTION 7.09.  Blue Sky.......................................................................  52
SECTION 7.10.  STC Stock Options..............................................................  52
SECTION 7.11.  [INTENTIONALLY LEFT BLANK].....................................................  53
SECTION 7.12.  Bridge Facility................................................................  53
SECTION 7.13.  Audited Financial Statements...................................................  54
SECTION 7.14.  Liquidity Takedowns; Additional Debt...........................................  55
SECTION 7.15.  Collateralization..............................................................  56
</TABLE>


                                       iii

<PAGE>   18
<TABLE>
<CAPTION>
                                                                                               Page
                                                                                               ----
                                  ARTICLE VIII

                            CONDITIONS TO THE MERGER
<S>           <C>                                                                              <C> 
SECTION 8.01. Conditions to the Obligations of Each Party to Consummate
                  the Merger..................................................................  56
SECTION 8.02.  Conditions to the Obligations of STC...........................................  57
SECTION 8.03.  Conditions to the Obligations of CGI...........................................  58
                                                                                               
                                                                                               
                                   ARTICLE IX
                                                                                               
                        TERMINATION, AMENDMENT AND WAIVER
                                                                                               
SECTION 9.01.  Termination....................................................................  59
SECTION 9.02.  Effect of Termination..........................................................  61
SECTION 9.03.  Amendment......................................................................  62
SECTION 9.04.  Waiver.........................................................................  62
SECTION 9.05.  Expenses.......................................................................  62
                                                                                               
                                                                                               
                                    ARTICLE X
                                                                                               
                               GENERAL PROVISIONS
                                                                                               
SECTION 10.01.  Non-Survival of Representations and Warranties................................  63
SECTION 10.02.  Notices.......................................................................  63
SECTION 10.03.  Severability..................................................................  63
SECTION 10.04.  Assignment; Binding Effect; Benefit...........................................  64
SECTION 10.05.  Incorporation of Exhibits.....................................................  64
SECTION 10.06.  Specific Performance..........................................................  64
SECTION 10.07.  Governing Law.................................................................  64
SECTION 10.08.  Waiver of Jury Trial..........................................................  64
SECTION 10.09.  Headings......................................................................  64
SECTION 10.10.  Counterparts..................................................................  65
SECTION 10.11.  Entire Agreement..............................................................  65
</TABLE>


                                       iv

<PAGE>   19
                                    EXHIBITS


Exhibit 1.00(a)   Form of STC Stock Option Agreement
Exhibit 1.00(b)   Form of CGI Stock Option Agreement
Exhibit 1.00(c)   Form of Bridge Facility Promissory Note
Exhibit 1.01(a)   Form of Stockholder Resolution Regarding the CGI Amendment
Exhibit 1.01(b)   Form of Stockholder Resolution Regarding the STC Amendment
Exhibit 7.03(a)   Form of STC Affiliate Agreement 
Exhibit 7.03(b)   Form of CGI Affiliate Agreement


                                       v

<PAGE>   20
                 AGREEMENT AND PLAN OF MERGER AND REORGANIZATION

         AGREEMENT AND PLAN OF MERGER AND REORGANIZATION, dated as of January
12, 1997 (as amended, supplemented or otherwise modified from time to time, this
"AGREEMENT"), among CELL GENESYS, INC., a corporation organized and existing
under the laws of the State of Delaware ("CGI"), S MERGER CORP., a corporation
organized and existing under the laws of the State of Delaware ("MERGER SUB")
and a direct wholly owned subsidiary of CGI, and SOMATIX THERAPY CORPORATION, a
corporation organized and existing under the laws of the State of Delaware
("STC");


                              W I T N E S S E T H:

         WHEREAS, the boards of directors of CGI, Merger Sub and STC have each
determined that it is fair to and in the best interests of their respective
stockholders for Merger Sub to merge (the "MERGER") with and into STC upon the
terms and subject to the conditions set forth herein and in accordance with the
General Corporation Law of the State of Delaware (the "GENERAL CORPORATION
LAW");

         WHEREAS, concurrently with the execution of this Agreement and as an
inducement to CGI and Merger Sub to enter into this Agreement, CGI, Merger Sub
and STC have entered into a stock option agreement, dated as of the date hereof
(the "STC STOCK OPTION AGREEMENT"), substantially in the form attached hereto as
Exhibit 1.00(a) pursuant to which STC has granted to Purchaser an option to
purchase from STC up to 5,441,480 shares of common stock, par value $.01 per
share, of STC (the "STC COMMON STOCK"), representing approximately 19.9 percent
of the shares of STC Common Stock issued and outstanding on the date hereof, at
a price of $3.51 per Share, all upon the terms and subject to the conditions set
forth therein;

         WHEREAS, concurrently with the execution of this Agreement and as an
inducement to STC to enter into this Agreement, CGI and STC have entered into a
stock option agreement, dated as of the date hereof (the "CGI STOCK OPTION
AGREEMENT"), substantially in the form attached hereto as Exhibit 1.00(b)
pursuant to which CGI has granted to STC an option to purchase from CGI up to
3,286,703 shares of common stock, par value $.001 per share, of CGI (the "CGI
COMMON STOCK"), representing approximately 19.9 percent of the shares of CGI
Common Stock issued and outstanding on the date hereof, at a price of $9.12 per
Share, all upon the terms and subject to the conditions set forth therein;

         WHEREAS, concurrently with the execution of this Agreement and as an
inducement to CGI and Merger Sub to enter into this Agreement, STC has made a
promissory note in favor of CGI, dated as of the date hereof (the "BRIDGE
FACILITY PROMISSORY NOTE"), substantially in the form attached hereto as Exhibit
1.00(c) pursuant to which STC has agreed to repay with interest the aggregate
principal amount of all Advances


<PAGE>   21
                                        2

(as defined below) made by CGI under the Bridge Facility (as defined below), all
upon the terms and subject to the conditions set forth therein; and

         WHEREAS, for United States federal income tax purposes, it is intended
that the Merger qualify as a reorganization under the provisions of Section 368
of the Internal Revenue Code of 1986, as amended (together with the rules and
regulations promulgated thereunder, the "CODE");

         NOW, THEREFORE, in consideration of the foregoing and the
representations, warranties, covenants and agreements set forth herein, and
other good and valuable consideration, the receipt and adequacy of which are
hereby acknowledged, and intending to be legally bound hereby, the parties
hereto hereby agree as follows:


                                    ARTICLE I

                                   DEFINITIONS

         SECTION 1.01. Certain Defined Terms. Unless the context otherwise
requires, the following terms, when used in this Agreement, shall have the
respective meanings specified below:

         "ACTUAL BALANCES" shall mean, on any specified date, the actual
balances of cash, cash equivalents and marketable securities held by STC on such
date.

         "AFFILIATE" shall have the meaning specified in Rule 144 promulgated
under the Securities Act.

         "AGREEMENT" shall have the meaning specified in the preamble to this
Agreement.

         "BENEFICIAL OWNER" shall mean, with respect to any shares of capital
stock, a person who shall be deemed to be the beneficial owner of such shares
(i) which such person or any of its affiliates or associates (as such term is
defined in Rule 12b-2 promulgated under the Exchange Act) beneficially owns,
directly or indirectly, (ii) which such person or any of its affiliates or
associates has, directly or indirectly, (A) the right to acquire (whether such
right is exercisable immediately or subject only to the passage of time),
pursuant to any agreement, arrangement or understanding or upon the exercise of
consideration rights, exchange rights, warrants or options, or otherwise, or (B)
the right to vote pursuant to any agreement, arrangement or understanding, or
(iii) which are beneficially owned, directly or indirectly, by any other persons
with whom such person or any of its affiliates or associates or person with whom
such person or any of its affiliates or associates has any agreement,


<PAGE>   22
                                        3


arrangement or understanding for the purpose of acquiring, holding, voting or
disposing of any such shares of capital stock.

         "BLUE SKY LAWS" shall mean state securities or "blue sky" laws.

         "BRIDGE FACILITY" shall mean the loan facility to be provided by CGI to
STC pursuant to, and upon the terms and subject to the conditions set forth in,
Section 7.12 and the Bridge Facility Promissory Note.

         "BRIDGE FACILITY MATURITY DATE" shall mean the earliest to occur of (i)
August 31, 1997; (ii) the 20th day after termination of this Agreement for any
reason whatsoever; (iii) notwithstanding the immediately preceding clause (ii),
the first business day after termination of this Agreement by CGI pursuant to
Section 9.01(d); (iv) the first business day after the board of directors of STC
changes, modifies, or withdraws its recommendation of the Merger in a manner
adverse to CGI; and (v) the day on which CGI declares its obligation to make
Advances to be terminated pursuant to the Bridge Facility Promissory Note with
respect to an Event of Default described in subsection (vi) or (vii) of the
definition of Event of Default contained in the Bridge Facility Promissory Note.

         "BRIDGE FACILITY PROMISSORY NOTE" shall have the meaning specified in
the recitals to this Agreement.

         "BUSINESS DAY" shall mean any day on which the principal offices of the
SEC in Washington, D.C. are open to accept filings, or, in the case of
determining a date when any payment is due, any day on which banks are not
required or authorized by law or executive order to close in San Francisco,
California.

         "CERTIFICATE OF MERGER" shall have the meaning specified in Section
2.03.

         "CGI" shall have the meaning specified in the preamble to this
Agreement.

         "CGI AFFILIATE AGREEMENT" shall have the meaning specified in Section
7.03(b).

         "CGI AMENDMENT" shall mean the proposed amendment, substantially in the
form attached hereto as Exhibit 1.01(a), to the certificate of incorporation of
CGI, to be included in the Joint Proxy Statement and voted on at CGI
Stockholders' Meeting.

         "CGI BENEFIT PLANS" shall have the meaning specified in Section
5.09(a).

         "CGI COMMON STOCK" shall have the meaning specified in the recitals to
this Agreement.


<PAGE>   23
                                        4


                  "CGI DIRECTOR" shall mean any person serving as a director of
CGI on the date hereof who remains a director of CGI after the Effective Time or
any other designee selected by CGI.

                  "CGI DISCLOSURE SCHEDULE" shall mean the disclosure schedule
delivered by CGI to STC prior to the execution of this Agreement and forming a
part hereof.

                  "CGI MATERIAL ADVERSE EFFECT" shall mean any change in or
effect on the business of CGI and the CGI Subsidiaries that is, or could
reasonably be expected to be, materially adverse to the business, assets
(including intangible assets), liabilities (contingent or otherwise), condition
(financial or otherwise) or results of operations of CGI and the CGI
Subsidiaries taken as a whole; provided, however, that any change in or effect
upon the business of CGI and the CGI Subsidiaries that directly or indirectly
arises out of or is attributable to (i) any decrease in the market price of CGI
Common Stock (but not any change or effect underlying such decrease to the
extent such change or effect would otherwise constitute a CGI Material Adverse
Effect) or (ii) circumstances or events that generally affect the industries in
which CGI or the CGI Subsidiaries operate, shall not constitute a CGI Material
Adverse Effect; provided further that the foregoing proviso shall not be deemed
to cause the condition contained in Section 8.02(a) or (b) not to have been
satisfied.

                  "CGI MATERIAL CONTRACT" shall have the meaning specified in
Section 5.11.

                  "CGI PERMITS" shall have the meaning specified in Section
5.06(a).

                  "CGI REPORTS" shall have the meaning specified in Section
5.07(a).

                  "CGI RIGHT" shall mean the preferred share purchase right to
be issued with respect to each share of CGI Common Stock issued to holders of
STC Capital Stock pursuant to the Merger as provided in Section 3(b) of the CGI
Rights Agreement.

                  "CGI RIGHTS AGREEMENT" shall mean the preferred shares rights
agreement, dated as of July 28, 1995, between CGI and The First National Bank of
Boston, as rights agent.

                  "CGI STOCK OPTION AGREEMENT" shall have the meaning specified
in the recitals to this Agreement.

                  "CGI STOCK PLANS" shall mean CGI's 1989 Incentive Stock Plan,
as amended, and 1992 Employee Stock Purchase Plan, as amended.


<PAGE>   24
                                        5


                  "CGI STOCKHOLDERS' MEETING" shall have the meaning specified
in Section 7.01(a).

                  "CGI SUBSIDIARIES" shall have the meaning specified in Section
5.01.

                  "CLOSING" shall have the meaning specified in Section 2.02.

                  "CODE" shall have the meaning specified in the recitals to
this Agreement.

                  "COMMITMENT TERMINATION EVENT" shall mean any of (i)
termination of this Agreement or the Bridge Facility Promissory Note for any
reason whatsoever; (ii) the occurrence of an Event of Default under the Bridge
Facility Promissory Note; (iii) a material breach of this Agreement or the
Bridge Facility Promissory Note; and (iv) the exercise of one or more of the
Fletcher Put Options or the consummation of any other Liquidity Takedown;
provided that, upon the occurrence of a Commitment Termination Event described
in this clause (iv), the commitment of CGI under the Bridge Facility shall only
be reduced on a dollar-for-dollar basis equal to the proceeds of any Liquidity
Takedown (e.g., a $2,000,000 Liquidity Takedown would reduce CGI's commitment
under the Bridge Facility to $3,000,000).

                  "COMMON EXCHANGE RATIO" shall have the meaning specified in
Section 3.01(a).

                  "COMPETING TRANSACTION" shall mean any of the following
involving CGI or STC, as the case may be (other than the Merger contemplated by
this Agreement):

                           (i)   any merger, consolidation, share exchange,
         business combination or other similar transaction;

                           (ii)  any sale, lease, exchange, mortgage, pledge,
         transfer or other disposition of 15 percent or more of the assets of
         such party and its subsidiaries, taken as a whole, in a single
         transaction or series of transactions;

                           (iii) any tender offer or exchange offer for 25
         percent or more of the outstanding voting securities of such party or
         the filing of a registration statement under the Securities Act in
         connection therewith; or

                           (iv)  any person having acquired beneficial ownership
         or the right to acquire beneficial ownership of, or any "group" (as
         such term is defined under Section 13(d) of the Exchange Act) having
         been formed which beneficially owns or has the right to acquire
         beneficial ownership of, 25 percent or more of the outstanding voting
         securities of such party;


<PAGE>   25
                                        6


                  (v)  any solicitation by any person (A) proposing any
     transaction described in clause (i), (ii), (iii) or (iv) above or (B) who
     is not a stockholder of CGI or STC on the date hereof, in opposition to the
     approval of this Agreement by the stockholders of CGI or STC; or

                  (vi) any public announcement of a proposal, plan or intention
     to do any of the foregoing or any agreement to engage in any of the
     foregoing.

         "CONFIDENTIALITY AGREEMENT" shall mean the confidentiality agreement,
dated as of October 14, 1996, between CGI and STC.

         "COSTS" shall have the meaning specified in Section 7.04(d).

         "DEA" the United States Drug Enforcement Administration.

         "DLJ" shall mean Donaldson, Lufkin & Jenrette, financial advisors to
STC.

         "$" shall mean United States Dollars.

         "EFFECTIVE TIME" shall have the meaning specified in Section 2.03.

         "ENVIRONMENTAL LAW" shall mean any Law and any enforceable judicial or
administrative interpretation thereof, including any judicial or administrative
order, consent decree or judgment, relating to pollution or protection of the
environment or natural resources, including, without limitation, those relating
to the use, handling, transportation, treatment, storage, disposal, release or
discharge of Hazardous Material, as in effect as of the date hereof.

         "ENVIRONMENTAL PERMIT" shall mean any permit, approval, identification
number, license or other authorization required under or issued pursuant to any
applicable Environmental Law.

         "ERISA" shall mean the Employee Retirement Income Security Act of 1974,
as amended.

         "EVENT OF DEFAULT" shall have the meaning specified in the Bridge
Facility Promissory Note.

         "EXCESS SHARES" shall have the meaning specified in Section 3.04(b).

         "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
amended, together with the rules and regulations promulgated thereunder.


<PAGE>   26
                                        7


         "EXCHANGE AGENT" shall have the meaning specified in Section 3.02.

         "EXCHANGE FUND" shall have the meaning specified in Section 3.02.

         "EXPENSES" shall mean, with respect to any party hereto, all reasonable
out-of-pocket expenses (including, without limitation, all fees and expenses of
counsel, accountants, investment bankers, experts and consultants to a party
hereto and its affiliates) incurred by such party or on its behalf in connection
with or related to the authorization, preparation, negotiation, execution and
performance of its obligations pursuant to this Agreement and the consummation
of the Merger, the preparation, printing, filing and mailing of the Registration
Statement and the Joint Proxy Statement, the solicitation of shareholder
approvals, the filing of HSR Act notice, if any, and all other matters related
to the closing of the Merger.

         "FDA" shall mean the United States Food and Drug Administration.

         "FDCA" shall mean the Federal Food, Drug, and Cosmetic Act, as amended.

         "FLETCHER" shall mean Fletcher International Limited, a company
organized under the laws of the Cayman Islands.

         "FLETCHER PUT OPTIONS" shall mean the put options granted by Fletcher
to STC pursuant to Section 1(a) of the subscription agreement, dated September
24, 1996, between STC and Fletcher and upon the terms and subject to the
conditions set forth in Annex A thereto.

         "FLETCHER WARRANT" shall mean the warrant, dated September 25, 1996,
issued by STC to and in the name of Fletcher.

         "GENERAL CORPORATION LAW" shall have the meaning specified in the
recitals to this Agreement.

         "GOVERNMENTAL ENTITY" shall mean any United States federal, state or
local or any foreign governmental, regulatory or administrative authority,
agency or commission or any court, tribunal or arbitral body.

         "GOVERNMENTAL ORDER" shall mean any order, writ, judgment, injunction,
decree, stipulation, determination or award entered by or with any Governmental
Entity.

         "HAZARDOUS MATERIAL" shall mean (i) any petroleum, petroleum products,
by-products or breakdown products, radioactive materials, asbestos-containing
materials or polychlorinated biphenyls or (ii) any chemical, material or
substance defined or regulated as


<PAGE>   27
                                        8


toxic or hazardous or as a pollutant or contaminant or waste under any
applicable Environmental Law.

         "HSR ACT" shall mean the Hart-Scott-Rodino Antitrust Improvements Act
of 1976, as amended, together with the rules and regulations promulgated
thereunder.

         "INDEMNIFIED PARTIES" shall have the meaning specified in Section
7.04(d).

         "IRS" shall mean the United States Internal Revenue Service.

         "JOINT PROXY STATEMENT" shall have the meaning specified in Section
7.01(a).

         "LAW" shall mean any federal, state or local statute, law, ordinance,
regulation, rule, code, order, other requirement or rule of law of the United
States or any other jurisdiction, including, without limitation, the FDCA, the
Controlled Substances Act, and any other similar act or law.

         "LEHMAN BROTHERS" shall mean Lehman Brothers, Inc., financial advisors
to CGI.

         "LIQUIDITY NOTICE" shall have the meaning specified in Section 7.12(b).

         "LIQUIDITY TAKEDOWN" shall have the meaning specified in Section
7.14(a).

         "MERGER" shall have the meaning specified in the recitals to this
Agreement.

         "MERGER SUB" shall have the meaning specified in the preamble to this
Agreement.

         "NASD" shall mean the National Association of Securities Dealers, Inc.

         "NEW FINANCING ADJUSTMENT AMOUNT" shall mean .3850 minus the quantity
 .3850 multiplied by the quotient of (i) (A) the aggregate number of shares of
CGI Common Stock issuable upon conversion of the STC Common Stock and the Series
A Preferred Stock pursuant to Sections 3.01(a) and 3.01(b), respectively, before
giving effect to clause (i), (ii) or (iii) in Section 3.01(a), minus (B) the
aggregate number of shares of CGI Common Stock issuable upon conversion of any
securities of STC issued thereby in connection with any Liquidity Takedown;
divided by (ii) the aggregate number of shares of CGI Common Stock issuable upon
conversion of the STC Common Stock and the Series A Preferred Stock pursuant to
Sections 3.01(a) and 3.01(b), respectively, before giving effect to clause (i),
(ii) or (iii) in Section 3.01(a). The purpose of the New Financing Adjustment
Amount is to ensure, and the New Financing Adjustment Amount shall be construed
so as to ensure, that


<PAGE>   28
                                        9


the number of shares of CGI Common Stock issuable pursuant to the Merger is the
same whether or not STC shall elect to issue in connection with any Liquidity
Takedown securities of STC convertible into shares of CGI Common Stock pursuant
to the Merger.

                  "NMS" shall mean the National Association of Securities
Dealers Automated Quotation System/National Market System.

                  "OPERATING BUDGET" shall have the meaning specified in Section
4.07(e).

                  "PERMITTED FINANCING" shall have the meaning specified in
Section 7.14(b).

                  "PERSON" shall mean an individual, corporation, partnership,
limited partnership, limited liability company, syndicate, person (including,
without limitation, a "person" as defined in Section 13(d)(3) of the Exchange
Act), trust, association, entity or government or political subdivision, agency
or instrumentality of a government.

                  "PRESURRENDER DIVIDENDS" shall have the meaning specified in
Section 3.02.

                  "PROJECTED CASH BALANCES" shall have the meaning specified in
Section 4.07(d).

                  "REGISTRATION STATEMENT" shall have the meaning specified in
Section 7.01(a).

                  "REPRESENTATIVES" shall have the meaning specified in Section
6.05(a).

                  "SEC" shall have the meaning specified in the recitals to this
Agreement.

                  "SECURITIES ACT" shall mean the Securities Act of 1933, as
amended, together with the rules and regulations promulgated thereunder.

                  "SERIES A EXCHANGE RATIO" shall have the meaning specified in
Section 3.01(b).

                  "SERIES A PREFERRED STOCK" shall mean the preferred stock of
STC designated as "Series A-1 Preferred Stock" and "Series A-2 Preferred Stock"
pursuant to the certificate of designation of preferences of preferred shares of
STC filed with the Secretary of State of the State of Delaware on June 29, 1995.

                  "SERIES B ADJUSTMENT AMOUNT" shall mean .3850 minus the
quantity .3850 multiplied by the quotient of (i) (A) the aggregate number of
shares of CGI Common Stock issuable upon conversion of the STC Common Stock and
the Series A Preferred Stock pursuant to Sections 3.01(a) and 3.01(b),
respectively, before giving effect to clause (i), (ii)


<PAGE>   29
                                       10


or (iii) in Section 3.01(a), minus (B) the product of (1) aggregate number of
shares of Series B Preferred Stock issued and outstanding immediately prior to
the Effective Time multiplied by (2) the Series B Exchange Ratio minus 16.4384;
divided by (ii) the aggregate number of shares of CGI Common Stock issuable upon
conversion of the STC Common Stock and the Series A Preferred Stock pursuant to
Sections 3.01(a) and 3.01(b), respectively, before giving effect to clause (i),
(ii) or (iii) in Section 3.01(a).

                  "SERIES B EXCHANGE RATIO" shall have the meaning specified in
Section 3.01(c).

                  "SERIES B PREFERRED STOCK" shall mean the preferred stock of
STC designated as "Series B-1 Preferred Stock" pursuant to the certificate of
designation of preferences of preferred shares of STC filed with the Secretary
of State of the State of Delaware on September 25, 1996.

                  "STC" shall have the meaning specified in the preamble to this
Agreement.

                  "STC AFFILIATE AGREEMENT" shall have the meaning specified in
Section 7.05(a).

                  "STC AMENDMENT" shall mean the proposed amendment,
substantially in the form attached hereto as Exhibit 1.01(b), to the certificate
of incorporation of STC, to be included in the Joint Proxy Statement and voted
on at the STC Stockholders' Meeting.

                  "STC BENEFIT PLANS" shall have the meaning specified in
Section 4.09(a).

                  "STC CAPITAL STOCK" shall mean the STC Common Stock, the
Series A Preferred Stock and the Series B Preferred Stock.

                  "STC COMMON STOCK" shall have the meaning specified in the
recitals to this Agreement.

                  "STC DIRECTOR" shall mean any person serving as a director of
STC on the date hereof who becomes a director of CGI at the Effective Time or
any other designee selected by STC.

                  "STC DISCLOSURE SCHEDULE" shall mean the disclosure schedule
delivered by STC to CGI prior to the execution of this Agreement and forming a
part hereof.

                  "STC MATERIAL ADVERSE EFFECT" shall mean any change in or
effect on the business of STC and the STC Subsidiaries that is, or could
reasonably be expected to be, materially adverse to the business, assets
(including intangible assets), liabilities (contingent


<PAGE>   30
                                       11


or otherwise), condition (financial or otherwise) or results of operations of
STC and the STC Subsidiaries taken as a whole; provided, however, that any
change in or effect upon the business of STC and the STC Subsidiaries that
directly or indirectly arises out of or is attributable to (i) the loss by STC
of any of its corporate partners (including, without limitation, any financial
consequence of such loss of corporate partners) due primarily to the public
announcement of this Agreement and the transactions contemplated hereby, (ii)
any decrease in the market price of the STC Common Stock (but not any change or
effect underlying such decrease to the extent such change or effect would
otherwise constitute an STC Material Adverse Effect), (iii) circumstances or
events that generally affect the industries in which STC or the STC Subsidiaries
operate, (iv) so long as STC has not breached Section 6.01 in any material
respect, any decrease in STC's cash balances and liquidity from the date hereof
and (v) in the event CGI has not, pursuant to Section 7.12, made available to
STC funds which, together with STC's then existing funds, are sufficient to
avoid the triggering of the rights specified in Section 7(B) of the certificate
of designation of STC applicable to the Series A Preferred Stock, the triggering
of such rights, shall not constitute an STC Material Adverse Effect; provided
further that the foregoing proviso shall not be deemed to cause the condition
contained in Section 8.03(a) or (b) not to have been satisfied.

                  "STC MATERIAL CONTRACT" shall have the meaning specified in
Section 4.11.

                  "STC PERMITS" shall have the meaning specified in Section
4.06(a).

                  "STC REPORTS" shall have the meaning specified in Section
4.07(a).

                  "STC STOCK OPTION" shall have the meaning specified in Section
3.05.

                  "STC STOCK OPTION AGREEMENT" shall have the meaning specified
in the recitals to this Agreement.

                  "STC STOCK PLANS" shall mean the Hana Biologics, Inc. 1988
Directors Stock Option Plan, STC's 1988 Stock Option Plan, as amended, the
GeneSys Therapeutic Corporation 1991 Stock Option Plan, STC's 1992 Stock Option
Plan, as amended, and the Merlin Pharmaceutical Corporation 1993 Stock Option
Plan.

                  "STC STOCKHOLDERS' MEETING" shall have the meaning specified
in Section 7.01(a).

                  "STC SUBSIDIARIES" shall have the meaning specified in Section
4.01.

                  "SUBSIDIARY" shall mean, with respect to any person, any
corporation, limited liability company, partnership, joint venture or other
legal entity of which such person (either


<PAGE>   31
                                       12


alone or through or together with any other subsidiary of such person) owns,
directly or indirectly, a majority of the stock or other equity interests, the
holders of which are generally entitled to vote for the election of the board of
directors or other governing body of such corporation or other legal entity.

                  "SURVIVING CORPORATION" shall have the meaning specified in
Section 2.01.

                  "TAXES" shall mean any and all taxes, fees, levies, duties,
tariffs, imposts and other charges of any kind (together with any and all
interest, penalties, additions to tax and additional amounts imposed with
respect thereto) imposed by any Governmental Entity or taxing authority,
including, without limitation, taxes or other charges on or with respect to
income, franchises, windfall or other profits, gross receipts, property, sales,
use, capital stock, payroll, employment, social security, workers' compensation,
unemployment compensation or net worth; taxes or other charges in the nature of
excise, withholding, ad valorem, stamp, transfer, value-added or gains taxes;
license, registration and documentation fees; and customers' duties, tariffs and
similar charges.

                  "TERMINATING CGI BREACH" shall have the meaning specified in
Section 9.01(h).

                  "TERMINATING STC BREACH" shall have the meaning specified in
Section 9.01(g).

                  "TRUST" shall have the meaning specified in Section 3.04(c).

                  "U.S. GAAP" shall mean United States generally accepted
accounting principles.


                                   ARTICLE II

                                   THE MERGER

                  SECTION 2.01. The Merger. Upon the terms and subject to the
conditions set forth in this Agreement, and in accordance with the General
Corporation Law, at the Effective Time, Merger Sub shall be merged with and into
STC. As a result of the Merger, the separate corporate existence of Merger Sub
shall cease and STC shall continue as the surviving corporation of the Merger
(the "SURVIVING CORPORATION").

                  SECTION 2.02. Closing. Unless this Agreement shall have been
terminated and the Merger shall have been abandoned pursuant to Section 9.01 and
subject to the satisfaction or waiver of the conditions set forth in Article
VIII, the consummation of the


<PAGE>   32
                                       13


Merger shall take place as promptly as practicable (and in any event within
three business days) after satisfaction or waiver of the conditions set forth in
Article VIII, at a closing (the "CLOSING") to be held at the offices of Shearman
& Sterling, 555 California Street, San Francisco, California, unless another
date, time or place is agreed to by STC and CGI.

                  SECTION 2.03. Effective Time. At the time of the Closing, the
parties shall cause the Merger to be consummated by filing a certificate of
merger (the "CERTIFICATE OF MERGER") with the Secretary of State of the State of
Delaware in such form as required by, and executed in accordance with the
relevant provisions of, the General Corporation Law (the date and time of such
filing being the "EFFECTIVE TIME").

                  SECTION 2.04. Effect of the Merger. At the Effective Time, the
effect of the Merger shall be as provided in the applicable provisions of the
General Corporation Law. Without limiting the generality of the foregoing, and
subject thereto, at the Effective Time, except as otherwise provided herein, all
the property, rights, privileges, powers and franchises of STC and Merger Sub
shall vest in the Surviving Corporation, and all debts, liabilities and duties
of STC and Merger Sub shall become the debts, liabilities and duties of the
Surviving Corporation.

                  SECTION 2.05. Certificate of Incorporation; By-laws; Directors
and Officers of Surviving Corporation. Unless otherwise agreed by STC and CGI
prior to the Effective Time, at the Effective Time:

                           (a) the certificate of incorporation and by-laws of
         Merger Sub, as in effect immediately prior to the Effective Time, shall
         be the certificate of incorporation and by-laws of the Surviving
         Corporation until thereafter amended as provided by Law and such
         certificate of incorporation or by-laws;

                           (b) the officers of Merger Sub immediately prior to
         the Effective Time shall be the initial officers of the Surviving
         Corporation until their successors are elected or appointed and
         qualified or until their resignation or removal; and

                           (c) the directors of Merger Sub immediately prior to
         the Effective Time shall be the initial directors of the Surviving
         Corporation until their successors are elected or appointed and
         qualified or until their resignation or removal.


<PAGE>   33
                                       14

                                   ARTICLE III

               CONVERSION OF SECURITIES; EXCHANGE OF CERTIFICATES

                  SECTION 3.01. Conversion of Securities. At the Effective Time,
by virtue of the Merger and without any action on the part of Merger Sub, STC or
the holders of any of the following securities:

                           (a) Each share of STC Common Stock issued and
         outstanding immediately prior to the Effective Time (other than any
         shares of STC Common Stock to be cancelled pursuant to Section 3.01(d))
         and all rights in respect thereof shall forthwith cease to exist and
         shall be converted into and become exchangeable for the number of
         shares of CGI Common Stock (and associated CGI Rights) equal to .3850
         minus (i) in the event that the Series B Exchange Ratio shall be
         greater than 16.4384, the Series B Adjustment Amount, (ii) in the event
         that the holder(s) of the Fletcher Warrant shall elect pursuant to the
         Fletcher Notice and in accordance with Section 10 of the Fletcher
         Warrant to put the Fletcher Warrant to, and have the Fletcher Warrant
         redeemed by, STC, .0063, and (iii) in the event that STC shall issue in
         connection with any Liquidity Takedown any securities convertible into
         shares of CGI Common Stock pursuant to this Section 3.01, the New
         Financing Adjustment Amount (after giving effect to such adjustments,
         if any, the "COMMON EXCHANGE RATIO");

                           (b) Each share of Series A Preferred Stock issued and
         outstanding immediately prior to the Effective Time (other than any
         shares of Series A Preferred Stock to be cancelled pursuant to Section
         3.01(d)) and all rights in respect thereof shall forthwith cease to
         exist and shall be converted into and become exchangeable for the
         number of shares of CGI Common Stock (and associated CGI Rights) equal
         to the product of 6.25 multiplied by the Common Exchange Ratio (the
         "SERIES A EXCHANGE RATIO");

                           (c) Each share of Series B Preferred Stock issued and
         outstanding immediately prior to the Effective Time (other than any
         shares of Series B Preferred Stock to be cancelled pursuant to Section
         3.01(d)) and all rights in respect thereof shall forthwith cease to
         exist and shall be converted into and become exchangeable for the
         number of shares of CGI Common Stock (and associated CGI Rights) equal
         to the quotient of $150.00 divided by the average of the daily closing
         prices of the CGI Common Stock over the 30-day period ending three days
         prior to the Effective Time (the "SERIES B EXCHANGE RATIO");

                           (d) Each share of STC Capital Stock held in the
         treasury of STC and each share of STC Capital Stock owned by CGI or any
         direct or indirect wholly


<PAGE>   34
                                       15


         owned subsidiary of CGI or of STC immediately prior to the Effective
         Time shall be cancelled and extinguished without any conversion thereof
         and no payment shall be made with respect thereto; and

                           (e) Each share of common stock, par value $.01 per
         share, of Merger Sub issued and outstanding immediately prior to the
         Effective Time and all rights in respect thereof shall forthwith cease
         to exist and shall be converted into and become exchangeable for one
         newly and validly issued, fully paid and nonassessable share of common
         stock of the Surviving Corporation.

                  SECTION 3.02. Exchange of Shares Other than Treasury Shares.
Subject to the terms and conditions hereof, at or prior to the Effective Time,
CGI shall appoint, and shall retain for a period of at least six months after
the Effective Time, an exchange agent to effect the exchange of shares of STC
Capital Stock for CGI Common Stock (and associated CGI Rights) in accordance
with the provisions of this Article III (the "EXCHANGE AGENT"). As soon as
reasonably practicable after the Effective Time, CGI will instruct the Exchange
Agent to mail to each holder of record of STC Capital Stock (i) a letter of
transmittal (which shall specify that delivery shall be effected, and risk of
loss and title to certificates evidencing shares of STC Capital Stock shall
pass, only upon proper delivery of such certificates to the Exchange Agent and
shall be in such form and have such other provisions as CGI may reasonably
specify) and (ii) instructions to effect the surrender of certificates
evidencing shares of STC Capital Stock in exchange for certificates evidencing
shares of CGI Common Stock (and associated CGI Rights) and, in lieu of any
fractional shares thereof, cash. From time to time after the Effective Time, CGI
shall deposit, or cause to be deposited, certificates representing CGI Common
Stock (and associated CGI Rights) for conversion of shares of STC Capital Stock
in accordance with the provisions of Section 3.01 (such certificates, together
with any dividends or distributions with respect thereto, being herein referred
to as the "EXCHANGE FUND"). Commencing immediately after the Effective Time and
until the appointment of the Exchange Agent shall be terminated, each holder of
a certificate or certificates theretofore evidencing shares of STC Capital Stock
may surrender the same, together with a duly executed letter of transmittal and
such other customary documents as CGI may reasonably require, to the Exchange
Agent, and, after the appointment of the Exchange Agent shall be terminated, any
such holder may surrender any such certificate, letter of transmittal and other
documents to CGI. Such holder shall be entitled upon such surrender to receive
in exchange therefor a certificate or certificates representing the number of
full shares of CGI Common Stock (and associated CGI Rights) into which the
shares of STC Capital Stock theretofore represented by the certificate or
certificates so surrendered shall have been converted in accordance with the
provisions of Section 3.01, together with a cash payment in lieu of fractional
shares, if any, in accordance with Section 3.04, and all such shares of CGI
Common Stock (and associated CGI Rights) shall be deemed to have been issued at
the Effective Time. Until so surrendered and exchanged, each outstanding
certificate which, prior to the Effective Time, represented


<PAGE>   35
                                       16


issued and outstanding shares of STC Capital Stock shall be deemed for all
corporate purposes of CGI, other than the payment of dividends and other
distributions, if any, to evidence ownership of the number of full shares of CGI
Common Stock (and associated CGI Rights) into which the shares of STC Capital
Stock theretofore represented thereby shall have been converted at the Effective
Time. Unless and until any such certificate theretofore representing shares of
STC Capital Stock is so surrendered, no dividend or other distribution, if any,
payable to the holders of record of CGI Common Stock as of any date subsequent
to the Effective Time shall be paid to the holder of such certificate in respect
thereof. Upon the surrender of any such certificate theretofore representing
shares of STC Capital Stock, however, the record holder of the certificate or
certificates representing shares of CGI Common Stock issued in exchange therefor
shall receive from the Exchange Agent or from CGI, as the case may be, payment
of the amount of dividends and other distributions, if any, which as of any date
subsequent to the Effective Time and until such surrender shall have become
payable with respect to such number of shares of CGI Common Stock ("PRESURRENDER
DIVIDENDS"). No interest shall be payable with respect to the payment of
Presurrender Dividends upon the surrender of certificates theretofore
representing shares of STC Capital Stock. After the appointment of the Exchange
Agent shall have been terminated, such holders of CGI Common Stock which have
not received payment of Presurrender Dividends shall look only to CGI for
payment thereof. Notwithstanding the foregoing provisions of this Section 3.02,
risk of loss and title to such certificates representing shares of STC Capital
Stock shall pass only upon proper delivery of such certificates to the Exchange
Agent, and neither the Exchange Agent nor any party hereto shall be liable to a
holder of shares of STC Capital Stock for any CGI Common Stock or dividends or
distributions thereon delivered to a public official pursuant to any applicable
abandoned property, escheat or similar law or to a transferee pursuant to
Section 3.03.

                  SECTION 3.03. Stock Transfer Books. At the Effective Time, the
stock transfer books of STC with respect to shares of STC Capital Stock shall
each be closed, and there shall be no further registration of transfers of
shares of STC Capital Stock thereafter on the records of any such stock transfer
books. In the event of a transfer of ownership of shares of STC Capital Stock
that is not registered in the stock transfer records of STC, at the Effective
Time, a certificate or certificates representing the number of full shares of
CGI Common Stock into which such shares of STC Capital Stock shall have been
converted shall be issued to the transferee together with a cash payment in lieu
of fractional shares, if any, in accordance with Section 3.04, and a cash
payment in the amount of Presurrender Dividends, if any, in accordance with
Section 3.02, if the certificate or certificates representing such shares of STC
Capital Stock is or are surrendered as provided in Section 3.02, accompanied by
all documents required to evidence and effect such transfer and by evidence of
payment of any applicable stock transfer tax.

                  SECTION 3.04. No Fractional Share Certificates. (a) No scrip
or fractional share certificate for CGI Common Stock shall be issued upon the
surrender for exchange of


<PAGE>   36
                                       17


certificates evidencing shares of STC Capital Stock, and an outstanding
fractional share interest shall not entitle the owner thereof (i) to vote, (ii)
to receive dividends or (iii) to any rights of a stockholder of CGI or of the
Surviving Corporation with respect to such fractional share interest.

                  (b) As promptly as practicable following the Effective Time,
the Exchange Agent shall determine the excess of (i) the number of full shares
of CGI Common Stock to be issued and delivered to the Exchange Agent pursuant to
Section 3.02 over (ii) the aggregate number of full shares of CGI Common Stock
to be distributed to holders of STC Capital Stock pursuant to Section 3.02 (such
excess being herein called the "EXCESS SHARES"). Following the Effective Time,
the Exchange Agent, as agent for the holders of STC Capital Stock, shall sell
the Excess Shares at then prevailing prices on the NMS, all in the manner
provided in subsection (c) of this Section 3.04.

                  (c) The sale of the Excess Shares by the Exchange Agent shall
be executed on the NMS through one or more member firms of such exchange and
shall be executed in round lots to the extent practicable. The Exchange Agent
shall use all reasonable efforts to complete the sale of the Excess Shares as
promptly following the Effective Time as, in the Exchange Agent's reasonable
judgment, is practicable consistent with obtaining the best execution of such
sales in light of prevailing market conditions. Until the net proceeds of such
sale or sales have been distributed to the holders of STC Capital Stock, the
Exchange Agent shall hold such proceeds in trust for the holders of STC Capital
Stock (the "TRUST"). CGI shall pay all commissions, transfer taxes and other
out-of-pocket transaction costs, including the expenses and compensation of the
Exchange Agent, incurred in connection with such sale of Excess Shares. The
Exchange Agent shall determine the portion of the Trust to which each holder of
STC Capital Stock shall be entitled, if any, by multiplying the amount of the
aggregate net proceeds comprising the Trust by a fraction the numerator of which
is the amount of fractional share interests to which such holder of STC Capital
Stock is entitled (after taking into account all shares of STC Capital Stock
held at the Effective Time by such holder) and the denominator of which is the
aggregate amount of fractional share interests to which all holders of STC
Capital Stock are entitled.

                  (d) Notwithstanding the provisions of subsections (b) and (c)
of this Section 3.04, CGI may, in lieu of the issuance and sale of Excess Shares
and the making of the payments contemplated in such subsections, pay to the
Exchange Agent an amount in cash sufficient for the Exchange Agent to pay each
holder of STC Capital Stock an amount in cash equal to the product obtained by
multiplying (i) the fractional share interest to which such holder would
otherwise be entitled (after taking into account all shares of STC Capital Stock
held at the Effective Time by such holder) by (ii) the closing price for a share
of CGI Common Stock on the NMS on the first business day immediately following
the Effective Time, and, in such case, all references herein to the cash
proceeds of the sale of the Excess Shares and similar references shall be deemed
to mean and refer to the payments calculated


<PAGE>   37
                                       18


as set forth in this subsection (d). In such event, Excess Shares shall not be
issued or otherwise transferred to the Exchange Agent pursuant to Section 3.02.

                  (e) As soon as practicable after the determination of the
amount of cash, if any, to be paid to holders of STC Capital Stock with respect
to any fractional share interests, the Exchange Agent shall make available such
amounts, net of any required withholding, excise or similar tax, to such holders
of STC Capital Stock, subject to and in accordance with the terms of Section
3.02.

                  (f) Any portion of the Exchange Fund or the Trust which
remains undistributed for six months after the Effective Time shall be delivered
to CGI, and any holder of STC Capital Stock who has not theretofore complied
with the provisions of this Article III shall thereafter look only to CGI for
satisfaction of their claims for CGI Common Stock or any cash in lieu of
fractional shares of CGI Common Stock and any Presurrender Dividends.

                  SECTION 3.05. Options and Warrants to Purchase STC Common
Stock. At the Effective Time, each option or warrant granted by STC to purchase
shares of STC Common Stock (each, an "STC STOCK OPTION") which is outstanding
and unexercised immediately prior to the Effective Time, shall be assumed by CGI
and converted into an option or warrant to purchase shares of CGI Common Stock
in such number and at such exercise price as provided below and otherwise having
the same terms and conditions as in effect immediately prior to the Effective
Time (except to the extent that such terms, conditions and restrictions may be
altered in accordance with their terms as a result of the Merger):

                           (a) the number of shares of CGI Common Stock to be
         subject to the new option or warrant shall be equal to the product of
         (i) the number of shares of STC Common Stock subject to the original
         option or warrant and (ii) the Common Exchange Ratio;

                           (b) the exercise price per share of CGI Common Stock
         under the new option or warrant shall be equal to the quotient of (i)
         the exercise price per share of STC Common Stock under the original
         option or warrant divided by (ii) the Common Exchange Ratio; and

                           (c) upon each exercise of options or warrants by a
         holder thereof, the aggregate number of shares of CGI Common Stock
         deliverable upon such exercise shall be rounded down, if necessary, to
         the nearest whole share and the aggregate exercise price shall be
         rounded up, if necessary, to the nearest cent.


<PAGE>   38
                                       19


The adjustments provided herein with respect to any options which are "incentive
stock options" (as defined in Section 422 of the Code) shall be effected in a
manner consistent with the requirements of Section 424(a) of the Code.

                  SECTION 3.06. Certain Adjustments. If between the date of this
Agreement and the Effective Time, the outstanding shares of STC Capital Stock or
CGI Common Stock shall be changed into a different number of shares by reason of
any reclassification, recapitalization, split-up, combination or exchange of
shares, or any dividend payable in stock or other securities shall be declared
thereon with a record date within such period, the exchange ratios established
pursuant to the provisions of Section 3.01 shall be adjusted accordingly to
provide to the holders of STC Capital Stock the same economic effect as
contemplated by this Agreement prior to such reclassification, recapitalization,
split-up, combination, exchange or dividend.


                                   ARTICLE IV

                      REPRESENTATIONS AND WARRANTIES OF STC

                  STC hereby represents and warrants to CGI and Merger Sub that:

                  SECTION 4.01. Organization and Qualification; Subsidiaries.
Each of STC and each subsidiary of STC (the "STC SUBSIDIARIES") has been duly
organized and is validly existing and in good standing (to the extent
applicable) under the laws of the jurisdiction of its incorporation or
organization, as the case may be, and has the requisite corporate power and
authority and all necessary governmental approvals to own, lease and operate its
properties and to carry on its business as it is now being conducted, except
where the failure to be so organized, existing or in good standing or to have
such power, authority and governmental approvals could not reasonably be
expected to have, individually or in the aggregate, an STC Material Adverse
Effect. Each of STC and each STC Subsidiary is duly qualified or licensed to do
business, and is in good standing (to the extent applicable), in each
jurisdiction where the character of the properties owned, leased or operated by
it or the nature of its business makes such qualification or licensing
necessary, except for such failures to be so qualified or licensed and in good
standing that could not reasonably be expected to have, individually or in the
aggregate, an STC Material Adverse Effect.

                  SECTION 4.02. Certificate of Incorporation and By-laws. The
copies of STC's certificate of incorporation and by-laws that are incorporated
by reference as exhibits to STC's Form 10-K for the period ending June 30, 1996
(the "STC 1996 10-K") are true, complete and correct copies thereof. Such
certificate of incorporation and by-laws are in full force and effect. STC is
not in violation of any of the provisions of its certificate of incorporation or
by-laws.


<PAGE>   39
                                       20


                  SECTION 4.03. Capitalization. The authorized capital stock of
STC consists of 40,000,000 shares of STC Common Stock and 1,000,000 shares of
preferred stock. As of January 6, 1997, (i) 27,344,121 shares of STC Common
Stock are issued and outstanding, all of which are validly issued, fully paid
and nonassessable, (ii) no shares of STC Common Stock are held in the treasury
of STC, (iii) no shares of STC Common Stock are held by the STC Subsidiaries,
(iv) 3,052,491 shares of STC Common Stock are reserved for future issuance
pursuant to employee stock options or stock incentive rights granted under the
STC Stock Plans, (v) 5,441,480 shares of STC Common Stock are reserved for
issuance pursuant to the STC Stock Option Agreement, (vi) 2,047,651 shares of
STC Common Stock are reserved for issuance upon conversion of the Series A
Preferred Stock, (vii) 1,500,000 shares of STC Common Stock are reserved for
issuance upon conversion of the Series B Preferred Stock, (viii) 224,000 shares
of Series A-1 Preferred Stock are issued and outstanding, (ix) 23,651 shares of
Series A-2 Preferred Stock are issued and outstanding and (x) 33,333 shares of
Series B Preferred Stock are issued and outstanding. There has been no change in
the capitalization of STC since January 6, 1997, excluding the exercise of
outstanding stock options. Except for the STC Stock Option Agreement and shares
of STC Common Stock issuable pursuant to the STC Stock Plans or pursuant to
agreements or arrangements described in Section 4.03 of the STC Disclosure
Schedule, and the warrants to purchase 889,000 shares of STC Common Stock issued
to holders of the Series A-1 Preferred Stock, there are no options, warrants or
other rights, agreements, arrangements or commitments of any character to which
STC is a party or by which STC is bound relating to the issued or unissued
capital stock of STC or any STC Subsidiary or obligating STC or any STC
Subsidiary to issue or sell any shares of capital stock of, or other equity
interests in, STC or any STC Subsidiary. All shares of STC Common Stock subject
to issuance as aforesaid, upon issuance prior to the Effective Time on the terms
and conditions specified in the instruments pursuant to which they are issuable,
will be duly authorized, validly issued, fully paid and nonassessable. Except
for the Fletcher Warrant, there are no outstanding contractual obligations of
STC or any STC Subsidiary to repurchase, redeem or otherwise acquire any shares
of STC Capital Stock or any capital stock of any STC Subsidiary. Each
outstanding share of capital stock of each STC Subsidiary is duly authorized,
validly issued, fully paid and nonassessable and each such share owned by STC or
another STC Subsidiary is free and clear of all security interests, liens,
claims, pledges, options, rights of first refusal, agreements, limitations on
STC's or such other STC Subsidiary's voting rights, charges and other
encumbrances of any nature whatsoever, except where the failure to own such
shares free and clear could not reasonably be expected to have, individually or
in the aggregate, an STC Material Adverse Effect. Except as set forth in Section
4.03 of the STC Disclosure Schedule, there are no material outstanding
contractual obligations of STC or any STC Subsidiary to provide funds to, or
make any material investment (in the form of a loan, capital contribution or
otherwise) in, any STC Subsidiary or any other person.

                  SECTION 4.04. Authority Relative to This Agreement and the STC
Stock Option Agreement. STC has all necessary corporate power and authority to
execute and


<PAGE>   40
                                       21


deliver this Agreement and the STC Stock Option Agreement, to perform its
obligations hereunder and thereunder and to consummate the transactions
contemplated hereby and thereby. The execution and delivery of this Agreement
and the STC Stock Option Agreement by STC and the consummation by STC of the
transactions contemplated hereby and thereby have been duly and validly
authorized by all necessary corporate action, and no other corporate proceedings
on the part of STC are necessary to authorize this Agreement or the STC Stock
Option Agreement or to consummate such transactions (other than the approval of
this Agreement and the Merger by the holders of a majority of the outstanding
shares of STC Capital Stock and Series A Preferred Stock entitled to vote with
respect thereto at the STC Stockholders' Meeting, in each case voting together
as a single class, and the filing and recordation of the Certificate of Merger
as required by the General Corporation Law). This Agreement and the STC Stock
Option Agreement have been duly executed and delivered by STC and, assuming the
due authorization, execution and delivery by the other parties hereto and
thereto, constitute legal, valid and binding obligations of STC, enforceable
against STC in accordance with their terms.

                  SECTION 4.05. No Conflict; Required Filings and Consents. (a)
The execution and delivery of this Agreement and the STC Stock Option Agreement
by STC do not, and the performance by STC of its obligations hereunder and
thereunder and the consummation of the Merger will not, (i) conflict with or
violate any provision of the certificate of incorporation or by-laws of STC or
any equivalent organizational documents of any STC Subsidiary, (ii) assuming
that all consents, approvals, authorizations and permits described in Section
4.05(b) have been obtained and all filings and notifications described in
Section 4.05(b) have been made, conflict with or violate any Law applicable to
STC or any STC Subsidiary or by which any property or asset of STC or any STC
Subsidiary is bound or affected or (iii) except as set forth in Section 4.05(a)
of the STC Disclosure Schedule, result in any breach of or constitute a default
(or an event which with the giving of notice or lapse of time or both could
reasonably be expected to become a default) under, or give to others any right
of termination, amendment, acceleration or cancellation of, or result in the
creation of a lien or other encumbrance on any property or asset of STC or any
STC Subsidiary pursuant to, any note, bond, mortgage, indenture, contract,
agreement, lease, license, permit, franchise or other instrument or obligation,
except, with respect to clauses (ii) and (iii), for any such conflicts,
violations, breaches, defaults or other occurrences which could not reasonably
be expected, individually or in the aggregate, (A) to have an STC Material
Adverse Effect or (B) to prevent or materially delay the performance by STC of
its obligations pursuant to this Agreement or the STC Stock Option Agreement or
the consummation of the Merger.

                  (b) The execution and delivery of this Agreement and the STC
Stock Option Agreement by STC do not, and the performance by STC of its
obligations hereunder and thereunder and the consummation of the Merger will
not, require any consent, approval, authorization or permit of, or filing by STC
with or notification by STC to, any


<PAGE>   41
                                       22

Governmental Entity except (i) pursuant to applicable requirements of the
Exchange Act, the Securities Act, Blue Sky Laws, the rules and regulations of
the NASD, state takeover laws, the premerger notification requirements of the
HSR Act, if any, and the filing and recordation of the Certificate of Merger as
required by the General Corporation Law, and (ii) where failure to obtain such
consents, approvals, authorizations or permits, or to make such filings or
notifications, could not reasonably be expected, individually or in the
aggregate, (A) to have an STC Material Adverse Effect or (B) to prevent or
materially delay the performance by STC of its obligations pursuant to this
Agreement or the STC Stock Option Agreement or the consummation of the Merger.

                  SECTION 4.06. Permits; Compliance with Laws. (a) STC and the
STC Subsidiaries are in possession of all franchises, grants, authorizations,
licenses, establishment registrations, product listings, permits, easements,
variances, exceptions, consents, certificates, approvals and orders of any
Governmental Entity, including, without limitation, the FDA, the DEA, and
similar authorities in other jurisdictions, necessary for STC or any STC
Subsidiary to own, lease and operate its properties or to produce, store,
distribute and market its products or otherwise to carry on its business as it
is now being conducted (the "STC PERMITS"), except where the failure to have, or
the suspension or cancellation of, any of the STC Permits could not reasonably
be expected to have, individually or in the aggregate, an STC Material Adverse
Effect, and, as of the date of this Agreement, no suspension or cancellation of
any of the STC Permits is pending or, to the knowledge of STC, threatened,
except where the failure to have, or the suspension or cancellation of, any of
the STC Permits could not reasonably be expected to have, individually or in the
aggregate, an STC Material Adverse Effect. Neither STC nor any STC Subsidiary is
in conflict with, or in default or violation of, (i) any Law applicable to STC
or any STC Subsidiary or by which any property or asset of STC or any STC
Subsidiary is bound or affected or (ii) any STC Permits, except in the case of
clauses (i) and (ii) for any such conflicts, defaults or violations that could
not reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect.

                  (b) Except as disclosed in the STC Reports or in Section
4.06(b) of the STC Disclosure Schedule or as could not reasonably be expected to
have, individually or in the aggregate, an STC Material Adverse Effect:

                           (i)  to the knowledge of STC, all of the clinical
         studies which have been, or are being, conducted by or for STC and the
         STC Subsidiaries are being conducted in substantial compliance with
         generally accepted good clinical practices and all applicable
         government regulatory requirements; and

                           (ii) to the knowledge of STC, none of STC, the STC
         Subsidiaries or any of their respective officers, employees or agents
         (during the term of such person's employment by STC or any STC
         Subsidiary or while acting as an agent of STC or


<PAGE>   42
                                       23


         any STC Subsidiary, or, to STC's knowledge, prior to such employment)
         has made any untrue statement of a material fact or fraudulent
         statement to the FDA or any similar Governmental Entity, failed to
         disclose a material fact required to be disclosed to the FDA or similar
         Governmental Entity, or committed an act, made a statement or failed to
         make a statement that could reasonably be expected to provide a basis
         for the FDA or similar Governmental Entity to invoke its policy
         respecting "Fraud, Untrue Statements of Material Facts, Bribery, and
         Illegal Gratuities" or similar governmental policy or Law.

                  SECTION 4.07. SEC Filings; Financial Statements; Projected
Cash Balances; Operating Budget. (a) Except as disclosed in Section 4.07 of the
STC Disclosure Schedule, STC has timely filed all forms, reports and documents
required to be filed by it with the SEC and the NASD since June 30, 1994 through
the date of this Agreement (collectively and as amended, the "STC REPORTS").
Each STC Report (i) was prepared in accordance with the requirements of the
Securities Act, the Exchange Act or the rules and regulations of the NASD, as
the case may be, and (ii) did not at the time it was filed contain any untrue
statement of a material fact or omit to state a material fact required to be
stated therein or necessary in order to make the statements made therein, in the
light of the circumstances under which they were made, not misleading. No STC
Subsidiary is subject to the periodic reporting requirements of the Exchange Act
or required to file any form, report or other document with the SEC, the NASD,
any other stock exchange or any other comparable Governmental Entity.

                   (b) Each of the consolidated financial statements (including,
in each case, any notes thereto) contained in the STC Reports was prepared, and
each of the consolidated financial statements (including, in each case, the
notes thereto) prepared and delivered pursuant to Section 7.13, if any, will be
prepared, in accordance with U.S. GAAP applied on a consistent basis throughout
the periods indicated (except as may be indicated in the notes thereto) and each
presented or will present fairly, in all material respects, the consolidated
financial position of STC and the consolidated STC Subsidiaries as at the
respective dates thereof and for the respective periods indicated therein,
except as otherwise noted therein (subject, in the case of unaudited statements,
to normal and recurring year-end adjustments which did not have and could not
reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect).

                   (c) Except as and to the extent set forth or reserved against
on the consolidated balance sheet of STC and the STC Subsidiaries as reported in
the STC Reports, including the notes thereto, none of STC or any STC Subsidiary
has any liabilities or obligations of any nature (whether accrued, absolute,
contingent or otherwise) that would be required to be reflected on a balance
sheet or in notes thereto prepared in accordance with U.S. GAAP, except for
liabilities or obligations incurred in the ordinary course of business


<PAGE>   43
                                       24


consistent with past practice since June 30, 1996 that have not had and could
not reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect.

                   (d) Within five days after the date hereof, STC shall furnish
CGI with a detailed schedule of STC's projected balances (the "PROJECTED CASH
BALANCES") of cash, cash equivalents and marketable securities of STC for each
month during the period from the date hereof through August 31, 1997. The
Projected Cash Balances will be prepared (and any revised Projected Cash
Balances delivered after the date hereof will be prepared) by senior management
of STC on the basis of assumptions and supplemental data which represent a
reasonable basis for such preparation, and will reflect (and any revised
Projected Cash Balances delivered after the date hereof will reflect) the best
currently available estimates and judgment of senior management of STC as to the
expected future balances of cash, cash equivalents and marketable securities of
the STC for the periods included.

                   (e) Within five days after the date hereof, STC shall furnish
CGI with a detailed schedule of STC's projected operating budget (the "OPERATING
BUDGET") of STC for each month during the period from the date hereof through
August 31, 1997. The Operating Budget will be prepared (and any revised
Operating Budget delivered after the date hereof will be prepared) by senior
management of STC on the basis of assumptions and supplemental data which
represent a reasonable basis for such preparation, and will reflect (and any
revised Operating Budget delivered after the date hereof will reflect) the best
currently available estimates and judgment of senior management of STC as to the
future operating expenses of STC expected to be incurred by STC in the ordinary
course consistent with past practice for the periods included.

                  SECTION 4.08. Absence of Certain Changes or Events. Since June
30, 1996, except as contemplated by or as disclosed in this Agreement, as set
forth in Section 4.08 of the STC Disclosure Schedule or as disclosed in any STC
Report filed since June 30, 1996, STC and the STC Subsidiaries have conducted
their businesses only in the ordinary course consistent with past practice and,
since such date, there has not been (i) any STC Material Adverse Effect
excluding any changes and effects resulting from changes in economic, regulatory
or political conditions or changes in conditions generally applicable to the
industries in which STC and the STC Subsidiaries are involved, (ii) any event
that could reasonably be expected to prevent or materially delay the performance
of its obligations pursuant to this Agreement and the consummation of the Merger
by STC, (iii) any material change by STC in its accounting methods, principles
or practices, (iv) any declaration, setting aside or payment of any dividend or
distribution in respect of the shares of STC Capital Stock or any redemption,
purchase or other acquisition of any of STC's securities or (v) any increase in
the compensation or benefits or establishment of any bonus, insurance,
severance, deferred compensation, pension, retirement, profit sharing, stock
option (including, without limitation, the granting of stock options, stock
appreciation rights, performance awards or restricted stock awards), stock
purchase or other employee benefit


<PAGE>   44
                                       25


plan, or any other increase in the compensation payable or to become payable to
any executive officers of STC or any STC Subsidiary except in the ordinary
course of business consistent with past practice.

                  SECTION 4.09. Employee Benefit Plans; Labor Matters. (a) With
respect to each employee benefit plan, program, arrangement and contract
(including, without limitation, any "employee benefit plan", as defined in
Section 3(3) of ERISA) maintained or contributed to by STC or any STC
Subsidiary, or with respect to which STC or any STC Subsidiary could incur
liability under Section 4069, 4212(c) or 4204 of ERISA (the "STC BENEFIT
PLANS"), STC has delivered or made available to CGI a true, complete and correct
copy of (i) such STC Benefit Plan and the most recent summary plan description
related to such STC Benefit Plan, if a summary plan description is required
therefor, (ii) each trust agreement or other funding arrangement relating to
such STC Benefit Plan, (iii) the most recent annual report (Form 5500) filed
with the IRS) with respect to such STC Benefit Plan, (iv) the most recent
actuarial report or financial statement relating to such STC Benefit Plan and
(v) the most recent determination letter issued by the IRS with respect to such
STC Benefit Plan, if it is qualified under Section 401(a) of the Code.

                  (b) Each STC Benefit Plan has been administered in all
material respects in accordance with its terms and all contributions required to
be made under the terms of any of the STC Benefit Plans as of the date of this
Agreement have been timely made or have been reflected on the most recent
consolidated balance sheet filed or incorporated by reference in the STC Reports
prior to the date of this Agreement. Except as set forth in Section 4.09(b) of
the STC Disclosure Schedule, with respect to the STC Benefit Plans, no event has
occurred and, to the knowledge of STC, there exists no condition or set of
circumstances in connection with which STC or any STC Subsidiary could be
subject to any liability under the terms of such STC Benefit Plans, ERISA, the
Code or any other applicable Law which could reasonably be expected to have,
individually or in the aggregate, an STC Material Adverse Effect.

                  (c) Except as set forth in Section 4.09(c) of the STC
Disclosure Schedule, neither STC nor any STC Subsidiary is a party to any
collective bargaining or other labor union contract applicable to persons
employed by STC or any STC Subsidiary and no collective bargaining agreement is
being negotiated by STC or any STC Subsidiary. As of the date of this Agreement,
there is no labor dispute, strike or work stoppage against STC or any STC
Subsidiary pending or, to the knowledge of STC, threatened which may interfere
with the respective business activities of STC or any STC Subsidiary, except
where such dispute, strike or work stoppage could not reasonably be expected to
have, individually or in the aggregate, an STC Material Adverse Effect. As of
the date of this Agreement, to the knowledge of STC, none of STC, any STC
Subsidiary, or any of their respective representatives or employees has
committed any unfair labor practice in connection with the operation of the
respective businesses of STC or any STC Subsidiary, and there is no charge


<PAGE>   45
                                       26


or complaint against STC or any STC Subsidiary by the National Labor Relations
Board or any comparable Governmental Entity pending or threatened in writing,
except where such unfair labor practice, charge or complaint could not
reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect.

                  (d) Except as set forth in Section 4.09(d) of the STC
Disclosure Schedule, STC has delivered to CGI true, complete and correct copies
of (i) all employment agreements with officers and employees and all consulting
agreements of STC and each STC Subsidiary providing for annual compensation in
excess of $25,000, (ii) all severance plans, agreements, programs and policies
of STC and each STC Subsidiary with or relating to their respective employees or
consultants, and (iii) all plans, programs, agreements and other arrangements of
STC and each STC Subsidiary with or relating to their respective employees or
consultants which contain "change of control" provisions.

                  (e) Except as provided in Section 4.09(e) of the STC
Disclosure Schedule or as otherwise required by Law, no STC Benefit Plan
provides retiree medical or retiree life insurance benefits to any person.

                  SECTION 4.10. Tax Matters. Except as disclosed in the STC
Reports, neither STC nor, to the knowledge of STC, any of its affiliates has
taken or agreed to take any action (other than actions contemplated by this
Agreement) that could reasonably be expected to prevent the Merger from
constituting a transaction qualifying under Section 368 of the Code. STC is not
aware of any agreement, plan or other circumstance that could reasonably be
expected to prevent the Merger from so qualifying under Section 368 of the Code.

                  SECTION 4.11. Contracts; Debt Instruments. Except as disclosed
in the STC Reports or in Section 4.11 of the STC Disclosure Schedule, there is
no contract or agreement that is material to the business, financial condition
or results of operations of STC and the STC Subsidiaries taken as a whole (each,
an "STC MATERIAL CONTRACT"). Except as disclosed in the STC Reports or in
Section 4.11 of the STC Disclosure Schedule, neither STC nor any STC Subsidiary
is in violation of or in default under (nor does there exist any condition which
with the passage of time or the giving of notice could reasonably be expected to
cause such a violation of or default under) any loan or credit agreement, note,
bond, mortgage, indenture or lease, or any other contract, license, agreement,
arrangement or understanding to which it is a party or by which it or any of its
properties or assets is bound, except for violations or defaults that could not
reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect. Set forth in Section 4.11 of the STC Disclosure
Schedule is a description of any material changes to the amount and terms of the
indebtedness of STC and its subsidiaries as described in the notes to the
financial statements incorporated in STC 1996 10-K.


<PAGE>   46
                                       27

                  SECTION 4.12. Litigation. Except as disclosed in the STC
Reports or in Section 4.12 of the STC Disclosure Schedule, there is no suit,
claim, action, proceeding or investigation pending or, to the knowledge of STC,
threatened against STC or any STC Subsidiary before any Governmental Entity that
could reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect, and, except as disclosed to CGI, to the knowledge of
STC, there are no existing facts or circumstances that could reasonably be
expected to result in such a suit, claim, action, proceeding or investigation.
For purposes hereof, nonmeritorious strike-suit litigation challenging the
execution, adoption or performance of this Agreement shall not be deemed
material. Except as disclosed to CGI, STC is not aware of any facts or
circumstances which could reasonably be expected to result in the denial of
insurance coverage under policies issued to STC and the STC Subsidiaries in
respect of such suits, claims, actions, proceedings and investigations, except
in any case as could not reasonably be expected to have, individually or in the
aggregate, an STC Material Adverse Effect. Except as disclosed in the STC
Reports or in Section 4.12 of the STC Disclosure Schedule, neither STC nor any
STC Subsidiary is subject to any outstanding order, writ, injunction or decree
which could reasonably be expected to have, individually or in the aggregate, an
STC Material Adverse Effect.

                  SECTION 4.13. Environmental Matters. Except as disclosed in
the STC Reports or in Section 4.13 of the STC Disclosure Schedule or as could
not reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect, (i) STC and the STC Subsidiaries are in compliance with
all applicable Environmental Laws; (ii) all past noncompliance of STC or any STC
Subsidiary with Environmental Laws or Environmental Permits has been resolved
without any pending, ongoing or future obligation, cost or liability; and (iii)
neither STC nor any STC Subsidiary has released a Hazardous Material at, or
transported a Hazardous Material to or from, any real property currently or
formerly owned, leased or occupied by STC or any STC Subsidiary, in violation of
any Environmental Law.

                  SECTION 4.14. Intellectual Property. Except as set forth in
Section 4.14 of the STC Disclosure Schedule, or as could not reasonably be
expected to have, individually or in the aggregate, an STC Material Adverse
Effect, STC and the STC Subsidiaries own or possess adequate licenses or other
valid rights to use all patents, patent rights, trademarks, trademark rights,
trade names, trade dress, trade name rights, copyrights, service marks, trade
secrets, applications for trademarks and for service marks, know-how and other
proprietary rights and information used or held for use in connection with the
respective businesses of STC and the STC Subsidiaries as currently conducted,
and STC is unaware of any assertion or claim challenging the validity of any of
the foregoing. Section 4.14 of the STC Disclosure Schedule lists all licenses,
sublicenses and other agreements to which STC or any STC Subsidiary is a party
and pursuant to which (i) any third party is authorized to use any intellectual
property right of STC or any STC Subsidiary and (ii) STC or any STC Subsidiary
is authorized to use any intellectual property rights (other than pursuant to
shrink-


<PAGE>   47
                                       28


wrap licenses and noncustomized software licenses) of a third party, and
includes the identity of all parties thereto, a description of the nature and
subject matter thereof, the royalty provisions, if any, therein and the term
thereof. Except as set forth in Section 4.14 of the STC Disclosure Schedule, the
conduct of the respective businesses of STC and the STC Subsidiaries as
currently conducted does not conflict in any way with any patent, patent right,
license, trademark, trademark right, trade dress, trade name, trade name right,
service mark or copyright of any third party that could not reasonably be
expected to have, individually or in the aggregate, an STC Material Adverse
Effect. To the knowledge of STC, there are no infringements of any proprietary
rights owned by or licensed by or to STC or any STC Subsidiary that could
reasonably be expected to have, individually or in the aggregate, an STC
Material Adverse Effect.

                  SECTION 4.15. Taxes. Except as set forth in Section 4.15 of
the STC Disclosure Schedule and except for such matters as could not reasonably
be expected to have, individually or in the aggregate, an STC Material Adverse
Effect, (i) each of STC and each STC Subsidiary has timely filed or shall timely
file all returns and reports required to be filed by it with any taxing
authority with respect to Taxes for any period ending on or before the Effective
Time, taking into account any extension of time to file granted to or obtained
on behalf of STC and the STC Subsidiaries, (ii) all Taxes shown to be payable on
such returns or reports that are due prior to the Effective Time have been or
will be paid, (iii) as of the date hereof, no deficiency for any amount of Tax
has been asserted or assessed by a taxing authority against STC or any STC
Subsidiary and (iv) each of STC and each STC Subsidiary has provided adequate
reserves in its financial statements for any Taxes that have not been paid,
whether or not shown as being due on any returns.

                  SECTION 4.16. Opinion of Financial Advisor. DLJ has delivered
to the board of directors of STC its written opinion to the effect that, as of
the date hereof, the Common Exchange Ratio, the Series A Exchange Ratio and the
Series B Exchange Ratio to be offered to the stockholders of STC in the proposed
transaction are fair to such stockholders from a financial point of view. DLJ
has authorized the inclusion of its opinion in the Joint Proxy Statement.

                  SECTION 4.17. Brokers. No broker, finder or investment banker
(other than DLJ) is entitled to any brokerage, finder's or other fee or
commission in connection with the Merger based upon arrangements made by or on
behalf of STC. STC has heretofore made available to CGI true, complete and
correct copies of all agreements between STC and DLJ pursuant to which such firm
would be entitled to any payment relating to the Merger.

                  SECTION 4.18. Certain Interests. (a) Except as set forth in
Section 4.18(a) of the STC Disclosure Schedule, no officer or director
(excluding outside directors) of STC or any STC Subsidiary, and no relative or
spouse (or relative of such spouse) who resides with, or is a dependent of, any
such officer or director:


<PAGE>   48
                                       29


                           (i)   has any direct or indirect financial interest 
         in any competitor of STC; provided, however, that the ownership of
         securities representing no more than two percent of the outstanding
         voting power of any competitor, supplier or customer, and which are
         also listed on any national securities exchange or traded actively in
         the national over-the-counter market, shall not be deemed to be a
         "financial interest" so long as the person owning such securities has
         no other connection or relationship with such competitor, supplier or
         customer;

                           (ii)  owns, directly or indirectly, in whole or in
         part, or has any other interest, in any tangible or intangible property
         which STC or any STC Subsidiary uses in the conduct of its business or
         otherwise; or

                           (iii) has outstanding any indebtedness to STC or any 
         STC Subsidiary.

                  (b) Except as set forth in Section 4.18(b) of the STC
Disclosure Schedule, neither STC nor any STC Subsidiary has any liability or any
other obligation of any nature whatsoever to any officer, director or
shareholder of STC or any STC Subsidiary, or to any relative or spouse (or
relative of such spouse) who resides with, or is a dependent of, any such
officer, director or shareholder, other than immaterial liabilities and
obligations incurred in the ordinary course of business which are reflected in
the STC Reports or with respect to which adequate reserves have been taken.


                                    ARTICLE V

              REPRESENTATIONS AND WARRANTIES OF CGI AND MERGER SUB

                  CGI and Merger Sub hereby jointly and severally represent and
warrant to STC that:

                  SECTION 5.01. Organization and Qualification; Subsidiaries.
Each of CGI, Merger Sub and each other subsidiary of CGI (the "CGI
SUBSIDIARIES") has been duly organized and is validly existing and in good
standing (to the extent applicable) under the laws of the jurisdiction of its
incorporation or organization, as the case may be, and has the requisite
corporate power and authority and all necessary governmental approvals to own,
lease and operate its properties and to carry on its business as it is now being
conducted, except where the failure to be so organized, existing or in good
standing or to have such power, authority and governmental approvals could not
reasonably be expected to have, individually or in the aggregate, a CGI Material
Adverse Effect. Each of CGI, Merger Sub and each other CGI Subsidiary is duly
qualified or licensed to do business, and is in good standing (to the extent
applicable), in each jurisdiction where the character of the properties


<PAGE>   49
                                       30


owned, leased or operated by it or the nature of its business makes such
qualification or licensing necessary, except for such failures to be so
qualified or licensed and in good standing that could not reasonably be expected
to have, individually or in the aggregate, a CGI Material Adverse Effect.

                  SECTION 5.02. Certificate of Incorporation and By-laws. Except
as set forth in Section 5.02 of the CGI Disclosure Schedule, the copies of CGI's
certificate of incorporation and by-laws that are incorporated by reference as
exhibits to CGI's Form 10-K for the period ending December 31, 1995 (the "CGI
1995 10-K") are true, complete and correct copies thereof. CGI has heretofore
furnished STC with true, complete and correct copies of the certificate of
incorporation and by-laws of Merger Sub. Such certificates of incorporation and
by-laws are in full force and effect. Neither CGI nor Merger Sub is in violation
of any of the provisions of its certificate of incorporation or by-laws.

                  SECTION 5.03. Capitalization. The authorized capital stock of
CGI consists of 25,000,000 shares of CGI Common Stock and 5,000,000 shares of
preferred stock. As of January 10, 1997, (i) 16,516,0099 shares of CGI Common
Stock are issued and outstanding, all of which are validly issued, fully paid
and nonassessable, (ii) no shares of CGI Common Stock are held in the treasury
of STC, (iii) no shares of CGI Common Stock are held by the CGI Subsidiaries,
(iv) 2,363,240 shares of CGI Common Stock are reserved for future issuance
pursuant to employee stock options or stock incentive rights granted under the
CGI Stock Plans and (v) 3,286,703 shares of CGI Common Stock are reserved for
issuance pursuant to the CGI Stock Option Agreement. As of the date hereof,
there are no shares of preferred stock of CGI issued and outstanding. Except for
the CGI Stock Option Agreement, shares of CGI Common Stock issuable pursuant to
the CGI Stock Plans or pursuant to agreements or arrangements described in
Section 5.03 of the CGI Disclosure Schedule, the CGI Rights issued and issuable
pursuant to the CGI Rights Plan, there are no options, warrants or other rights,
agreements, arrangements or commitments of any character to which CGI is a party
or by which CGI is bound relating to the issued or unissued capital stock of
CGI, Merger Sub or any other CGI Subsidiary or obligating CGI, Merger Sub or any
other CGI Subsidiary to issue or sell any shares of capital stock of, or other
equity interests in, CGI, Merger Sub or any other CGI Subsidiary. All shares of
CGI Common Stock subject to issuance as aforesaid, upon issuance prior to the
Effective Time on the terms and conditions specified in the instruments pursuant
to which they are issuable, will be duly authorized, validly issued, fully paid
and nonassessable. There are no outstanding contractual obligations of CGI,
Merger Sub or any other CGI Subsidiary to repurchase, redeem or otherwise
acquire any shares of CGI Common Stock or any capital stock of any CGI
Subsidiary. Each outstanding share of capital stock of each CGI Subsidiary is
duly authorized, validly issued, fully paid and nonassessable and each such
share owned by CGI or another CGI Subsidiary is free and clear of all security
interests, liens, claims, pledges, options, rights of first refusal, agreements,
limitations on CGI's or such other CGI Subsidiary's voting rights, charges and
other encumbrances of any nature whatsoever, except


<PAGE>   50
                                       31


where the failure to own such shares free and clear could not reasonably be
expected to have, individually or in the aggregate, a CGI Material Adverse
Effect. Except as set forth in Section 5.03 of the CGI Disclosure Schedule,
there are no material outstanding contractual obligations of CGI, Merger Sub or
any other CGI Subsidiary to provide funds to, or make any material investment
(in the form of a loan, capital contribution or otherwise) in, any CGI
Subsidiary or any other person.

                  SECTION 5.04. Authority Relative to This Agreement and the CGI
Stock Option Agreement. CGI and Merger Sub have all necessary corporate power
and authority to execute and deliver this Agreement and the CGI Stock Option
Agreement, to perform their respective obligations hereunder and thereunder and
to consummate the transactions contemplated hereby and thereby. The execution
and delivery of this Agreement and the CGI Stock Option Agreement by CGI and
Merger Sub and the consummation by CGI and Merger Sub of the transactions
contemplated hereby and thereby have been duly and validly authorized by all
necessary corporate action, and no other corporate proceedings on the part of
CGI or Merger Sub are necessary to authorize this Agreement or the CGI Stock
Option Agreement or to consummate such transactions (other than the approval of
this Agreement and the Merger by the holders of a majority of the votes cast by
CGI's stockholders with respect thereto at the CGI Stockholders' Meeting and the
filing and recordation of the Certificate of Merger as required by the General
Corporation Law). This Agreement and the CGI Stock Option Agreement have been
duly executed and delivered by CGI and Merger Sub and, assuming the due
authorization, execution and delivery by STC, constitute legal, valid and
binding obligations of CGI and Merger Sub, enforceable against CGI and Merger
Sub in accordance with their terms.

                  SECTION 5.05. No Conflict; Required Filings and Consents. (a)
The execution and delivery of this Agreement and the CGI Stock Option Agreement
by CGI and Merger Sub do not, and the performance by CGI and Merger Sub of their
obligations hereunder and thereunder and the consummation of the Merger will
not, (i) conflict with or violate any provision of the certificate of
incorporation or by-laws of CGI or Merger Sub or any equivalent organizational
documents of any other CGI Subsidiary, (ii) assuming that all consents,
approvals, authorizations and permits described in Section 5.05(b) have been
obtained and all filings and notifications described in Section 5.05(b) have
been made, conflict with or violate any Law applicable to CGI or any other CGI
Subsidiary or by which any property or asset of CGI, Merger Sub or any other CGI
Subsidiary is bound or affected or (iii) except as set forth in Section 5.05(a)
of the CGI Disclosure Schedule, result in any breach of or constitute a default
(or an event which with the giving of notice or lapse of time or both could
reasonably be expected to become a default) under, or give to others any right
of termination, amendment, acceleration or cancellation of, or result in the
creation of a lien or other encumbrance on any property or asset of CGI, Merger
Sub or any other CGI Subsidiary pursuant to, any note, bond, mortgage,
indenture, contract, agreement, lease, license, permit, franchise or other
instrument or obligation, except, with respect to clauses


<PAGE>   51
                                       32

(ii) and (iii), for any such conflicts, violations, breaches, defaults or other
occurrences which could not reasonably be expected, individually or in the
aggregate, (A) to have a CGI Material Adverse Effect or (B) to prevent or
materially delay the performance by CGI or Merger Sub of its obligations
pursuant to this Agreement or the CGI Stock Option Agreement or the consummation
of the Merger.

                  (b) The execution and delivery of this Agreement and the CGI
Stock Option Agreement by CGI and Merger Sub do not, and the performance by CGI
and Merger Sub of their respective obligations hereunder and thereunder and the
consummation of the Merger will not, require any consent, approval,
authorization or permit of, or filing by CGI or Merger Sub with or notification
by CGI or Merger Sub to, any Governmental Entity, except (i) pursuant to
applicable requirements of the Exchange Act, the Securities Act, Blue Sky Laws,
the rules and regulations of the NASD, state takeover laws, the premerger
notification requirements of the HSR Act, if any, and the filing and recordation
of the Certificate of Merger as required by the General Corporation Law and (ii)
where failure to obtain such consents, approvals, authorizations or permits, or
to make such filings or notifications, could not reasonably be expected,
individually or in the aggregate, (A) to have a CGI Material Adverse Effect or
(B) to prevent or materially delay the performance by CGI or Merger Sub of its
obligations pursuant to this Agreement or the CGI Stock Option Agreement or the
consummation of the Merger.

                  SECTION 5.06. Permits; Compliance with Laws. (a) Each of CGI,
Merger Sub and each other CGI Subsidiary is in possession of all franchises,
grants, authorizations, licenses, establishment registrations, product listings,
permits, easements, variances, exceptions, consents, certificates, approvals and
orders of any Governmental Entity, including, without limitation, the FDA, the
DEA and similar authorities in other jurisdictions, necessary for it to own,
lease and operate its properties or to store, distribute and market its products
or otherwise to carry on its business as it is now being conducted (the "CGI
PERMITS"), except where the failure to have, or the suspension or cancellation
of, any of the CGI Permits could not reasonably be expected to have,
individually or in the aggregate, a CGI Material Adverse Effect, and, as of the
date of this Agreement, no suspension or cancellation of any of the CGI Permits
is pending or, to the knowledge of CGI, threatened, except where the failure to
have, or the suspension or cancellation of, any of the CGI Permits could not
reasonably be expected to have, individually or in the aggregate, a CGI Material
Adverse Effect. None of CGI, Merger Sub or any other CGI Subsidiary is in
conflict with, or in default or violation of, (i) any Law applicable to CGI,
Merger Sub or any other CGI Subsidiary or by which any property or asset of CGI,
Merger Sub or any other CGI Subsidiary is bound or affected or (ii) any CGI
Permits, except in the case of clauses (i) and (ii) for any such conflicts,
defaults or violations that could not reasonably be expected to have,
individually or in the aggregate, a CGI Material Adverse Effect.


<PAGE>   52
                                       33

                  (b) Except as disclosed in the CGI Reports or in Section
5.06(b) of the CGI Disclosure Schedule or as could not reasonably be expected to
have, individually or in the aggregate, a CGI Material Adverse Effect:

                           (i) to the knowledge of CGI, all of the clinical
         studies which have been, or are being, conducted by or for CGI and the
         CGI Subsidiaries are being conducted in substantial compliance with
         generally accepted good clinical practices and all applicable
         government regulatory requirements; and

                           (ii) to the knowledge of CGI, none of CGI, the CGI
         Subsidiaries or any of their respective officers, employees or agents
         (during the term of such person's employment by CGI or any CGI
         Subsidiary or while acting as an agent of CGI or any CGI Subsidiary,
         or, to CGI's knowledge, prior to such employment) has made any untrue
         statement of a material fact or fraudulent statement to the FDA or any
         similar Governmental Entity, failed to disclose a material fact
         required to be disclosed to the FDA or similar Governmental Entity, or
         committed an act, made a statement or failed to make a statement that
         could reasonably be expected to provide a basis for the FDA or similar
         Governmental Entity to invoke its policy respecting "Fraud, Untrue
         Statements of Material Facts, Bribery, and Illegal Gratuities" or
         similar governmental policy or Law.

                  SECTION 5.07. SEC Filings; Financial Statements. (a) Except as
disclosed in Section 5.07 of the CGI Disclosure Schedule, CGI has timely filed
all forms, reports and documents required to be filed by it with the SEC and the
NASD since December 31, 1993 through the date of this Agreement (collectively
and as amended, the "CGI Reports"). Each CGI Report (i) was prepared in
accordance with the requirements of the Securities Act, the Exchange Act or the
NASD, as the case may be, and (ii) did not at the time it was filed contain any
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary in order to make the statements made therein, in
the light of the circumstances under which they were made, not misleading. No
CGI Subsidiary is subject to the periodic reporting requirements of the Exchange
Act or required to file any form, report or other document with the SEC, the
NASD, any other stock exchange or any other comparable Governmental Entity.

                  (b) Each of the consolidated financial statements (including,
in each case, any notes thereto) contained in the CGI Reports was prepared in
accordance with U.S. GAAP applied on a consistent basis throughout the periods
indicated (except as may be indicated in the notes thereto) and each presented
fairly, in all material respects, the consolidated financial position of CGI and
the consolidated CGI Subsidiaries as at the respective dates thereof and for the
respective periods indicated therein, except as otherwise noted therein
(subject, in the case of unaudited statements, to normal and recurring year-end
<PAGE>   53
                                       34

adjustments which did not and could not reasonably be expected to have,
individually or in the aggregate, a CGI Material Adverse Effect).

                  (c) Except as and to the extent set forth or reserved against
on the consolidated balance sheet of CGI and its Subsidiaries as reported in the
CGI Reports, including the notes thereto, none of CGI or any CGI Subsidiary has
any liabilities or obligations of any nature (whether accrued, absolute,
contingent or otherwise) that would be required to be reflected on a balance
sheet or in notes thereto prepared in accordance with U.S. GAAP, except for
liabilities or obligations incurred in the ordinary course of business
consistent with past practice since December 31, 1995 that have not had and
could not reasonably be expected to have, individually or in the aggregate, a
CGI Material Adverse Effect.

                  SECTION 5.08. Absence of Certain Changes or Events. Since
December 31, 1995, except as contemplated by or as disclosed in this Agreement,
as set forth in Section 5.08 of the CGI Disclosure Schedule or as disclosed in
any CGI Report filed since December 31, 1995, CGI and the CGI Subsidiaries have
conducted their businesses only in the ordinary course consistent with past
practice and, since such date, there has not been (i) any CGI Material Adverse
Effect excluding any changes and effects resulting from changes in economic,
regulatory or political conditions or changes in conditions generally applicable
to the industries in which CGI and the CGI Subsidiaries are involved, (ii) any
event that could reasonably be expected to prevent or materially delay the
performance of their obligations pursuant to this Agreement and the consummation
of the Merger by Merger Sub, (iii) any material change by CGI in its accounting
methods, principles or practices, (iv) any declaration, setting aside or payment
of any dividend or distribution in respect of the shares of CGI Common Stock or
any redemption, purchase or other acquisition of any of CGI's securities or (v)
any increase in the compensation or benefits or establishment of any bonus,
insurance, severance, deferred compensation, pension, retirement,
profit-sharing, stock option (including, without limitation, the granting of
stock options, stock appreciation rights, performance awards or restricted stock
awards), stock purchase or other employee benefit plan, or any other increase in
the compensation payable or to become payable to any executive officers of CGI
or any CGI Subsidiary except in the ordinary course of business consistent with
past practice.

                  SECTION 5.09. Employee Benefit Plans; Labor Matters. (a) With
respect to each employee benefit plan, program, arrangement and contract
(including, without limitation, any "employee benefit plan", as defined in
Section 3(3) of ERISA) maintained or contributed to by CGI or any CGI
Subsidiary, or with respect to which CGI or any CGI Subsidiary could incur
liability under Section 4069, 4212(c) or 4204 of ERISA (the "CGI Benefit Plans",
CGI has delivered or made available to STC a true, complete and correct copy of
(i) such CGI Benefit Plan and the most recent summary plan description related
to such CGI Benefit Plan, if a summary plan description is required therefor,
(ii) each
<PAGE>   54
                                       35

trust agreement or other funding arrangement relating to such CGI Benefit Plan,
(iii) the most recent annual report (Form 5500) filed with the IRS with respect
to such CGI Benefit Plan, (iv) the most recent actuarial report or financial
statement relating to such CGI Benefit Plan and (v) the most recent
determination letter issued by the IRS with respect to such CGI Benefit Plan, if
it is qualified under Section 401(a) of the Code.

                  (b) Each CGI Benefit Plan has been administered in all
material respects in accordance with its terms and all contributions required to
be made under the terms of any of the CGI Benefit Plans as of the date of this
Agreement have been timely made or have been reflected on the most recent
consolidated balance sheet filed or incorporated by reference in the CGI Reports
prior to the date of this Agreement. Except as set forth in Section 5.09(b) of
the CGI Disclosure Schedule, with respect to the CGI Benefit Plans, no event has
occurred and, to the knowledge of CGI, there exists no condition or set of
circumstances in connection with which CGI or any CGI Subsidiary could be
subject to any liability under the terms of such CGI Benefit Plans, ERISA, the
Code or any other applicable Law which could reasonably be expected to have,
individually or in the aggregate, a CGI Material Adverse Effect.

                  (c) Except as set forth in Section 5.09(c) of the CGI
Disclosure Schedule, neither CGI nor any CGI Subsidiary is a party to any
collective bargaining or other labor union contract applicable to persons
employed by CGI or any CGI Subsidiary and no collective bargaining agreement is
being negotiated by CGI or any CGI Subsidiary. As of the date of this Agreement,
there is no labor dispute, strike or work stoppage against CGI or any CGI
Subsidiary pending or, to the knowledge of CGI, threatened which may interfere
with the respective business activities of CGI or any CGI Subsidiary, except
where such dispute, strike or work stoppage could not reasonably be expected to
have, individually or in the aggregate, a CGI Material Adverse Effect. As of the
date of this Agreement, to the knowledge of CGI, none of CGI, any CGI
Subsidiary, or any of their respective representatives or employees has
committed any unfair labor practice in connection with the operation of the
respective businesses of CGI or any CGI Subsidiary, and there is no charge or
complaint against CGI or any CGI Subsidiary by the National Labor Relations
Board or any comparable Governmental Entity pending or threatened in writing,
except where such unfair labor practice, charge or complaint could not
reasonably be expected to have, individually or in the aggregate, a CGI Material
Adverse Effect.

                  (d) CGI has delivered to STC true, complete and correct copies
of (i) all employment agreements with officers of CGI and each CGI Subsidiary
providing for annual compensation in excess of $25,000, (ii) all severance
plans, agreements, programs and policies of CGI and each CGI Subsidiary with or
relating to their respective employees and (iii) all plans, programs, agreements
and other arrangements of CGI and each CGI Subsidiary with or relating to their
respective employees which contain "change of control" provisions.
<PAGE>   55
                                       36


                  (e) Except as provided in Section 5.09(e) of the CGI
Disclosure Schedule or as otherwise required by Law, no CGI Benefit Plan
provides retiree medical or retiree life insurance benefits to any person.

                  SECTION 5.10. Tax Matters. Except as disclosed in the CGI
Reports, neither CGI nor, to the knowledge of CGI, any of its affiliates has
taken or agreed to take any action (other than actions contemplated by this
Agreement) that could reasonably be expected to prevent the Merger from
constituting a transaction qualifying under Section 368 of the Code. CGI is not
aware of any agreement, plan or other circumstance that could reasonably be
expected to prevent the Merger from so qualifying under Section 368 of the Code.

                  SECTION 5.11. Contracts; Debt Instruments. Except as disclosed
in the CGI Reports or in Section 5.11 of the CGI Disclosure Schedule, there is
no contract or agreement that is material to the business, financial condition
or results of operations of CGI and the CGI Subsidiaries taken as a whole (each,
a "CGI Material Contract"). Except as disclosed in the CGI Reports or in Section
5.11 of the CGI Disclosure Schedule, neither CGI nor any CGI Subsidiary is in
violation of or in default under (nor does there exist any condition which with
the passage of time or the giving of notice could reasonably be expected to
cause such a violation of or default under) any loan or credit agreement, note,
bond, mortgage, indenture or lease, or any other contract, license, agreement,
arrangement or understanding to which it is a party or by which it or any of its
properties or assets is bound, except for violations or defaults that could not
reasonably be expected to have, individually or in the aggregate, a CGI Material
Adverse Effect. Set forth in Section 5.11 of the CGI Disclosure Schedule is a
description of any material changes to the amount and terms of the indebtedness
of CGI and its subsidiaries as described in the notes to the financial
statements incorporated in the CGI 1995 10-K.

                  SECTION 5.12. Litigation. Except as disclosed in the CGI
Reports or in Section 5.12 of the CGI Disclosure Schedule, there is no suit,
claim, action, proceeding or investigation pending or, to the knowledge of CGI,
threatened against CGI or any CGI Subsidiary before any Governmental Entity that
could reasonably be expected to have, individually or in the aggregate, a CGI
Material Adverse Effect, and, except as disclosed to STC, to the knowledge of
CGI, there are no existing facts or circumstances that could reasonably be
expected to result in such a suit, claim, action, proceeding or investigation.
For purposes hereof, nonmeritorious strike-suit litigation challenging the
execution, adoption or performance of this Agreement shall not be deemed
material. Except as disclosed to STC, CGI is not aware of any facts or
circumstances which could reasonably be expected to result in the denial of
insurance coverage under policies issued to CGI and the CGI Subsidiaries in
respect of such suits, claims, actions, proceedings and investigations, except
in any case as could not reasonably be expected to have, individually or in the
aggregate, a CGI Material Adverse Effect. Except as disclosed in the CGI Reports
or in Section 5.12 of
<PAGE>   56
                                       37

the CGI Disclosure Schedule, neither CGI nor any CGI Subsidiary is subject to
any outstanding order, writ, injunction or decree which could reasonably be
expected to have, individually or in the aggregate, a CGI Material Adverse
Effect.

                  SECTION 5.13. Environmental Matters. Except as disclosed in
the CGI Reports or in Section 5.13 of the CGI Disclosure Schedule or as could
not reasonably be expected to have, individually or in the aggregate, a CGI
Material Adverse Effect, (i) CGI and the CGI Subsidiaries are in compliance with
all applicable Environmental Laws; (ii) all past noncompliance of CGI or any CGI
Subsidiary with Environmental Laws or Environmental Permits has been resolved
without any pending, ongoing or future obligation, cost or liability; and (iii)
neither CGI nor any CGI Subsidiary has released a Hazardous Material at, or
transported a Hazardous Material to or from, any real property currently or
formerly owned, leased or occupied by CGI or any CGI Subsidiary in violation of
any Environmental Law.

                  SECTION 5.14. Intellectual Property. Except as disclosed in
Section 5.14 of the CGI Disclosure Schedule or as could not reasonably be
expected to have, individually or in the aggregate, a CGI Material Adverse
Effect, CGI and the CGI Subsidiaries own or possess adequate licenses or other
valid rights to use all patents, patent rights, trademarks, trademark rights,
trade names, trade dress, trade name rights, copyrights, service marks, trade
secrets, applications for trademarks and for service marks, know-how and other
proprietary rights and information used or held for use in connection with the
respective businesses of CGI and the CGI Subsidiaries as currently conducted,
and CGI is unaware of any assertion or claim challenging the validity of any of
the foregoing. Section 5.14 of the CGI Disclosure Schedule lists all licenses,
sublicenses and other agreements to which CGI or any CGI Subsidiary is a party
and pursuant to which (i) any third party is authorized to use any intellectual
property right of CGI or any CGI Subsidiary and (ii) CGI or any CGI Subsidiary
is authorized to use any intellectual property rights (other than pursuant to
shrink- wrap licenses and noncustomized software licenses) of a third party, and
includes the identity of all parties thereto, a description of the nature and
subject matter thereof, the royalty provisions, if any, therein and the term
thereof. Except as set forth in Section 5.14 of the CGI Disclosure Schedule, the
conduct of the respective businesses of CGI and the CGI Subsidiaries as
currently conducted does not conflict in any way with any patent, patent right,
license, trademark, trademark right, trade dress, trade name, trade name right,
service mark or copyright of any third party that could reasonably be expected
to have, individually or in the aggregate, a CGI Material Adverse Effect. Except
as disclosed in Section 5.14 of the CGI Disclosure Schedule, to the knowledge of
CGI, there are no infringements of any proprietary rights owned by or licensed
by or to CGI or any CGI Subsidiary that could reasonably be expected to have,
individually or in the aggregate, a CGI Material Adverse Effect.
<PAGE>   57
                                       38

                  SECTION 5.15. Taxes. Except as set forth in Section 5.15 of
the CGI Disclosure Schedule and except for such matters as could not reasonably
be expected to have, individually or in the aggregate, a CGI Material Adverse
Effect, (i) each of CGI, Merger Sub and each other CGI Subsidiary has timely
filed or shall timely file all returns and reports required to be filed by it
with any taxing authority with respect to Taxes for any period ending on or
before the Effective Time, taking into account any extension of time to file
granted to or obtained on behalf of CGI, Merger Sub and the other CGI
Subsidiaries, (ii) all Taxes shown to be payable on such returns or reports that
are due prior to the Effective Time have been or will be paid, (iii) as of the
date hereof, no deficiency for any amount of Tax has been asserted or assessed
by a taxing authority against CGI, Merger Sub or any other CGI Subsidiary and
(iv) each of CGI, Merger Sub and each other CGI Subsidiary has provided adequate
reserves in its financial statements for any Taxes that have not been paid,
whether or not shown as being due on any returns.

                  SECTION 5.16. Opinion of Financial Advisor. Lehman Brothers
has delivered to the board of directors of CGI its written opinion to the effect
that, as of the date hereof, each of the Common Exchange Ratio, the Series A
Exchange Ratio and the Series B Exchange Ratio is fair to the holders of shares
of CGI Common Stock from a financial point of view. Lehman Brothers has
authorized the inclusion of its opinion in the Joint Proxy Statement.

                  SECTION 5.17. Brokers. No broker, finder or investment banker
(other than Lehman Brothers) is entitled to any brokerage, finder's or other fee
or commission in connection with the Merger based upon arrangements made by or
on behalf of CGI. CGI has heretofore made available to STC true, complete and
correct copies of all agreements between CGI and Lehman Brothers pursuant to
which such firm would be entitled to any payment relating to the Merger.

                  SECTION 5.18. Certain Interests. (a) Except as set forth in
Section 5.18(a) of the CGI Disclosure Schedule or in the CGI SEC Reports, no
officer or director (excluding outside directors) of CGI or any CGI Subsidiary,
and no relative or spouse (or relative of such spouse) who resides with, or is a
dependent of, any such shareholder, officer or director:

                           (i) has any direct or indirect financial interest in
         any competitor; provided, however, that the ownership of securities
         representing no more than two percent of the outstanding voting power
         of any competitor, supplier or customer, and which are also listed on
         any national securities exchange or traded actively in the national
         over-the-counter market, shall not be deemed to be a "financial
         interest" so long as the person owning such securities has no other
         connection or relationship with such competitor, supplier or customer;
<PAGE>   58
                                       39

                           (ii) owns, directly or indirectly, in whole or in
         part, or has any other interest in any tangible or intangible property
         which CGI or any CGI Subsidiary uses in the conduct of its business or
         otherwise; or

                           (iii) has outstanding any indebtedness to CGI or any 
         CGI Subsidiary.

                  (b) Except as set forth in Section 5.18(b) of the CGI
Disclosure Schedule, neither CGI nor any CGI Subsidiary has any liability or any
other material obligation of any nature whatsoever to any officer or director of
CGI or any CGI Subsidiary, or to any relative or spouse (or relative of such
spouse) who resides with, or is a dependent of, any such officer or director,
other than immaterial liabilities and obligations incurred in the ordinary
course of business which are reflected in the CGI Reports or with respect to
which adequate reserves have been taken.


                                   ARTICLE VI

                                    COVENANTS

                  SECTION 6.01. Conduct of Business by STC Pending the Closing.
STC agrees that, between the date of this Agreement and the Effective Time,
except as set forth in Section 6.01 of the STC Disclosure Schedule or as
expressly contemplated by any other provision of this Agreement, unless CGI
shall otherwise agree in writing, (x) the respective businesses of STC and the
STC Subsidiaries shall be conducted only in, and STC and the STC Subsidiaries
shall not take any action except in, the ordinary course of business consistent
with past practice and (y) STC shall use all reasonable efforts to keep
available the services of such of the current officers, employees and
consultants of STC and the STC Subsidiaries and to preserve the current
relationships of STC and the STC Subsidiaries with such of the corporate
partners, customers, suppliers and other persons with which STC or any STC
Subsidiary has significant business relations in order to preserve substantially
intact its business organization. By way of amplification and not limitation,
except as set forth in Section 6.01 of the STC Disclosure Schedule or as
expressly contemplated by any other provision of this Agreement and the STC
Stock Option Agreement, neither STC nor any STC Subsidiary shall, between the
date of this Agreement and the Effective Time, directly or indirectly, do, or
agree to do, any of the following without the prior written consent of CGI,
which consent shall not be unreasonably withheld or delayed:

                           (a) amend or otherwise change its certificate of 
         incorporation or by-laws or equivalent organizational documents;

                           (b) issue, sell, pledge, dispose of, grant, transfer,
         lease, license, guarantee or encumber, or authorize the issuance, sale,
         pledge, disposition, grant,
<PAGE>   59
                                       40

         transfer, lease, license or encumbrance of, (i) any shares of capital
         stock of STC or any STC Subsidiary of any class, or securities
         convertible into or exchangeable or exercisable for any shares of such
         capital stock, or any options, warrants or other rights of any kind to
         acquire any shares of such capital stock, or any other ownership
         interest (including, without limitation, any phantom interest), of STC
         or any STC Subsidiary, except for (A) issuances of STC Common Stock
         pursuant to options and warrants thereon outstanding on the date hereof
         and described in Section 4.03 and (B) issuances of non-cash dividends
         required to be made under the terms of the certificate of designation
         of STC applicable to the Series A Preferred Stock, or (ii) any property
         or assets of STC or any STC Subsidiary;

                           (c) (i) acquire (including, without limitation, by
         merger, consolidation, or acquisition of stock or assets) any interest
         in any corporation, partnership, other business organization or person
         or any division thereof or any assets, other than acquisitions of
         assets; (ii) incur any indebtedness for borrowed money or issue any
         debt securities or assume, guarantee or endorse, or otherwise as an
         accommodation become responsible for, the obligations of any person for
         borrowed money; (iii) terminate, cancel or request any material change
         in, or agree to any material change in, any STC Material Contract or
         enter into any corporate partnering transaction or similar arrangement
         or any other contract or agreement material to the business, results of
         operations or financial condition of STC and the STC Subsidiaries taken
         as a whole; (iv) make or authorize any capital expenditure, except for
         capital expenditures not in excess of $5,000 individually and $50,000
         in the aggregate; provided that CGI will not unreasonably withhold its
         consent to reasonable expenditures in excess thereof; or (v) enter into
         or amend any contract, agreement, commitment or arrangement that, if
         fully performed, would not be permitted under this Section 6.01(c);

                           (d) declare, set aside, make or pay any dividend or
         other distribution, payable in cash, stock, property or otherwise, with
         respect to any of its capital stock or the Fletcher Warrant, except
         that any STC Subsidiary may pay dividends or make other distributions
         to STC or any other STC Subsidiary and may pay noncash dividends
         required to be made under the terms of the certificate of designation
         of STC applicable to the Series A Preferred Stock;

                           (e) reclassify, combine, split, subdivide or redeem,
         purchase or otherwise acquire, directly or indirectly, any of its 
         capital stock;

                           (f) increase the compensation payable or to become
         payable to its officers, consultants or employees, or grant any rights
         to severance or termination pay to, or enter into any employment or
         severance agreement which provides benefits upon a change in control of
         STC that would be triggered by the Merger with, any
<PAGE>   60
                                       41

         director, officer, consultant or other employee of STC or any STC
         Subsidiary who is not currently entitled to such benefits from the
         Merger, or establish, adopt, enter into or amend any collective
         bargaining, bonus, profit-sharing, thrift, compensation, stock option,
         restricted stock, pension, retirement, deferred compensation,
         employment, termination, severance or other plan, agreement, trust,
         fund, policy or arrangement for the benefit of any director, officer,
         consultant or employee of STC or any STC Subsidiary, except to the
         extent required by applicable Law or the terms of a collective
         bargaining agreement;

                           (g) take any action with respect to accounting 
         policies or procedures, other than actions in the ordinary course of 
         business consistent with past practice or as required by U.S. GAAP;

                           (h) make any tax election or settle or compromise any
         material federal, state or local United States income tax liability, or
         any income tax liability of any other jurisdiction, other than those
         made in the ordinary course of business consistent with past practice
         and those for which specific reserves have been recorded on the
         consolidated balance sheet of STC and the consolidated STC Subsidiaries
         dated as of June 30, 1996 included in the 1996 STC 10-K and only to the
         extent of such reserves; or

                           (i) authorize or enter into any formal or informal 
         agreement or otherwise make any commitment to do any of the foregoing.

                  SECTION 6.02. Conduct of Business by CGI Pending the Closing.
CGI agrees that, between the date of this Agreement and the Effective Time,
except as set forth in Section 6.02 of the CGI Disclosure Schedule or as
expressly contemplated by any other provision of this Agreement, unless STC
shall otherwise agree in writing, (x) the respective businesses of CGI and the
CGI Subsidiaries shall be conducted only in, and CGI and the CGI Subsidiaries
shall not take any action except in, the ordinary course of business consistent
with past practice and (y) CGI shall use all reasonable efforts to keep
available the services of such of the current officers, significant employees
and consultants of CGI and the CGI Subsidiaries and to preserve the current
relationships of CGI and the CGI Subsidiaries with such of the corporate
partners, customers, suppliers and other persons with which CGI or any CGI
Subsidiary has significant business relations as CGI deems reasonably necessary
in order to preserve substantially intact its business organization. By way of
amplification and not limitation, except as set forth in Section 6.02 of the CGI
Disclosure Schedule or as expressly contemplated by any other provision of this
Agreement and the CGI Stock Option Agreement, neither CGI nor any CGI Subsidiary
shall, between the date of this Agreement and the Effective Time, directly or
indirectly, do, or agree to do, any of the following without the prior written
consent of STC, which consent shall not be unreasonably withheld or delayed:
<PAGE>   61
                                       42


                           (a) amend or otherwise change its certificate of 
         incorporation or by-laws or equivalent organizational documents;

                           (b) issue, sell, pledge, dispose of, grant, transfer,
         lease, license, guarantee or encumber, or authorize the issuance, sale,
         pledge, disposition, grant, transfer, lease, license or encumbrance of,
         (i) any shares of capital stock of CGI or any CGI Subsidiary of any
         class, or securities convertible into or exchangeable or exercisable
         for any shares of such capital stock, or any options, warrants or other
         rights of any kind to acquire any shares of such capital stock, or any
         other ownership interest (including, without limitation, any phantom
         interest), of CGI or any CGI Subsidiary, except for (A) issuances of
         CGI Common Stock pursuant to options and warrants thereon outstanding
         on the date hereof and described in Section 5.03, (B) issuances of
         options to new hires of CGI and (C) issuances of options to employees,
         officers and directors of CGI consistent with past practice, or (ii)
         any property or assets of CGI or any CGI Subsidiary, except in the
         ordinary course of business consistent with past practice and pursuant
         to any existing CGI Material Contract or in an aggregate amount not in
         excess of $10,000,000;

                           (c) (i) acquire (including, without limitation, by
         merger, consolidation or acquisition of stock or assets) any interest
         in any corporation, partnership, other business organization or person
         or any division thereof or any assets, other than acquisitions of
         assets (excluding the acquisition of a business or substantially all of
         the stock or assets thereof) in the ordinary course of business
         consistent with past practice, and any acquisitions for consideration,
         calculated as of the date of execution of the definitive agreement for
         any such acquisition, that is not, in the aggregate for all such
         acquisitions, in excess of 10 percent of the market value of CGI of the
         date of the execution of any contract related thereto; (ii) incur any
         indebtedness for borrowed money or issue any debt securities or assume,
         guarantee or endorse, or otherwise as an accommodation become
         responsible for, the obligations of any person for borrowed money;
         (iii) terminate, cancel or request any material change in, or agree to
         any material change in, any CGI Material Contract or enter into any
         contract or agreement material to the business, results of operations
         or financial condition of CGI and the CGI Subsidiaries taken as a
         whole, in either case other than in the ordinary course of business
         consistent with past practice; (iv) make or authorize any capital
         expenditure, other than capital expenditures in the ordinary course of
         business consistent with past practice; or (v) enter into or amend any
         contract, agreement, commitment or arrangement that, if fully
         performed, would not be permitted under this Section 6.02(c);

                           (d) declare, set aside, make or pay any dividend or 
         other distribution, payable in cash, stock, property or otherwise, 
         with respect to any of its
<PAGE>   62
                                       43

         capital stock, except that any CGI Subsidiary may pay dividends or make
         other distributions to CGI or any other CGI Subsidiary;

                           (e) reclassify, combine, split, subdivide or redeem,
         purchase or otherwise acquire, directly or indirectly, any of its 
         capital stock;

                           (f) increase the compensation payable or to become
         payable to its officers or employees, except for increases in
         accordance with past practices in salaries or wages of employees or
         officers of CGI or any CGI Subsidiary (including, without limitation,
         annual merit increases and bonuses), or grant any rights to severance
         or termination pay to, or enter into any employment or severance
         agreement which provides benefits upon a change in control of CGI that
         would be triggered by the Merger with, any director, officer or other
         employee of CGI or any CGI Subsidiary who is not currently entitled to
         such benefits upon the Merger, or establish, adopt, enter into or amend
         any collective bargaining, bonus, profit-sharing, thrift, compensation,
         stock option, restricted stock, pension, retirement, deferred
         compensation, employment, termination, severance or other plan,
         agreement, trust, fund, policy or arrangement for the benefit of any
         director, officer or employee of CGI or any CGI Subsidiary, except to
         the extent required by applicable Law or the terms of a collective
         bargaining agreement;

                           (g) take any action with respect to accounting 
         policies or procedures, other than actions in the ordinary course of 
         business consistent with past practice or as required by U.S. GAAP;

                           (h) make any tax election or settle or compromise any
         material federal, state or local United States income tax liability, or
         any income tax liability of any other jurisdiction, other than those
         made in the ordinary course of business consistent with past practice
         and those for which specific reserves have been recorded on the
         consolidated balance sheet of CGI and the consolidated CGI Subsidiaries
         dated as of December 31, 1995 included in the 1995 CGI 10-K and only to
         the extent of such reserves; or

                           (i) authorize or enter into any formal or informal 
         agreement or otherwise make any commitment to do any of the foregoing.

                  SECTION 6.03. Cooperation; Steering Committee. Upon the
execution and delivery of this Agreement, CGI and STC shall establish a
committee (the "Steering Committee") for the purpose of, to the extent permitted
by applicable Laws, facilitating the efficient transition and combination of the
respective businesses of CGI and STC as promptly as practicable following the
Effective Time. The Steering Committee shall consist of up to 10 individuals to
be designated from time to time by the Chairman of CGI in consultation
<PAGE>   63
                                       44

with the Chairman of STC, and shall be chaired by CGI. The Steering Committee
shall be dissolved as of the Effective Time.

                  SECTION 6.04. Notices of Certain Events. Each of CGI and STC
shall give prompt notice to the other of (i) any notice or other communication
from any person alleging that the consent of such person is or may be required
in connection with the Merger; (ii) any notice or other communication from any
Governmental Entity in connection with the Merger; (iii) any actions, suits,
claims, investigations or proceedings commenced or, to its knowledge, threatened
against, relating to or involving or otherwise affecting CGI, STC, the CGI
Subsidiaries or the STC Subsidiaries that relate to the consummation of the
Merger; (iv) the occurrence of a default or event that, with the giving of
notice or lapse of time or both, will become a default under any STC Material
Contract or CGI Material Contract; and (v) any change that could reasonably be
expected to have an STC Material Adverse Effect or a CGI Material Adverse Effect
or to delay or impede the ability of either STC or CGI to perform its
obligations pursuant to this Agreement, the STC Stock Option Agreement or the
CGI Stock Option Agreement and to effect the consummation of the Merger.

                  SECTION 6.05. Access to Information; Confidentiality. (a)
Except as required pursuant to any confidentiality agreement or similar
agreement or arrangement to which CGI or STC or any of the CGI Subsidiaries or
the STC Subsidiaries is a party or pursuant to applicable Law or the regulations
or requirements of any stock exchange or other regulatory organization with
whose rules a party hereto is required to comply, from the date of this
Agreement to the Effective Time, CGI and STC shall (and shall cause the CGI
Subsidiaries and the STC Subsidiaries, respectively, to) (i) provide to the
other (and its officers, directors, employees, accountants, consultants, legal
counsel, agents and other representatives (collectively, "Representatives"))
access at reasonable times upon prior notice to its and its subsidiaries'
officers, employees, agents, properties, offices and other facilities and to the
books and records thereof, and (ii) furnish promptly such information concerning
its and its subsidiaries' business, properties, contracts, assets, liabilities
and personnel as the other party or its Representatives may reasonably request.
No investigation conducted pursuant to this Section 6.05 shall affect or be
deemed to modify any representation or warranty made in this Agreement.

                  (b) The parties hereto shall comply with, and shall cause
their respective Representatives to comply with, all of their respective
obligations under the Confidentiality Agreement with respect to the information
disclosed pursuant to this Section 6.05.

                  SECTION 6.06. No Solicitation of Transactions. Each party to
this Agreement shall not, directly or indirectly, and shall instruct its
officers, directors, employees, subsidiaries, agents or advisors or other
representatives (including, without limitation, any investment banker, attorney
or accountant retained by it), not to, directly or indirectly, solicit, initiate
or knowingly encourage (including by way of furnishing nonpublic
<PAGE>   64
                                       45

information), or take any other action knowingly to facilitate, any inquiries or
the making of any proposal or offer (including, without limitation, any proposal
or offer to its stockholders) that constitutes, or may reasonably be expected to
lead to, any Competing Transaction, or enter into or maintain or continue
discussions or negotiate with any person in furtherance of such inquiries or to
obtain a Competing Transaction, or agree to or endorse any Competing
Transaction, or authorize or permit any of the officers, directors or employees
of such party or any of its subsidiaries, or any investment banker, financial
advisor, attorney, accountant or other representative retained by such party or
any of such party's subsidiaries, to take any such action; provided, however,
that nothing contained in this Section 6.06 shall prohibit the board of
directors of CGI or STC from (i) complying with Rule 14e-2 promulgated under the
Exchange Act with regard to a tender or exchange offer or (ii) after receiving
the advice of outside counsel to the effect that the board of directors of STC
or CGI, as the case may be, is required to do so in order to discharge properly
its fiduciary duties, considering, negotiating and approving and recommending to
the shareholders of STC or CGI, as the case may be, an unsolicited bona fide
written acquisition proposal which (A) was not received in violation of this
Section 6.06, (B) if executed or consummated would be a Competing Transaction,
(C) is not subject to financing and (D) the board of directors of STC or CGI, as
the case may be, determines in good faith, after consultation with its financial
advisors, would result in a transaction more favorable to STC's or CGI's
stockholders, as the case may be, than the transaction contemplated by this
Agreement (any such acquisition proposal, a "Superior Proposal"). Each party
hereto shall notify the other parties hereto promptly if any proposal or offer,
or any inquiry or contact with any person with respect thereto, regarding such
an acquisition proposal or a Competing Transaction is made. Each party hereto
immediately shall cease and cause to be terminated all existing discussions or
negotiations with any parties conducted heretofore with respect to a Competing
Transaction. None of the parties hereto shall release any third party from, or
waive any provision of, any confidentiality or standstill agreement to which it
is a party. Each party hereto shall use its best efforts to ensure that its
officers, directors, employees and subsidiaries and any investment banker or
other advisor or representative retained by such party are aware of the
restrictions described in this Section 6.06.

                  SECTION 6.07. Plan of Reorganization. This Agreement is
intended to constitute a "plan of reorganization" within the meaning of Section
1.368-2(g) of the income tax regulations promulgated under the Code. From and
after the date of this Agreement, each party hereto shall use all reasonable
efforts to cause the Merger to qualify, and shall not, without the prior written
consent of the other parties hereto, knowingly take any actions or cause any
actions to be taken which could reasonably be expected to prevent the Merger
from qualifying, as a reorganization under the provisions of Section 368 of the
Code. In the event that the Merger shall fail to qualify as a reorganization
under the provisions of Section 368 of the Code, then the parties hereto agree
to negotiate in good faith to restructure the Merger in order that shall qualify
as tax-free transaction under the Code. Following the Effective Time, and
consistent with any such consent, neither the Surviving
<PAGE>   65
                                       46

Corporation nor CGI nor any of their respective affiliates knowingly and
voluntarily shall take any action or cause any action to be taken which could
reasonably be expected to cause the Merger to fail to qualify as a
reorganization under Section 368 of the Code.

                  SECTION 6.08. Subsequent Financial Statements. Prior to the
Effective Time, each of STC and CGI (i) shall consult with the other prior to
making publicly available its financial results for any period and (ii) shall
consult with the other prior to the filing of, and shall timely file with the
SEC, each Annual Report on Form 10-K, Quarterly Report on Form 10-Q and Current
Report on Form 8-K required to be filed by such party under the Exchange Act and
shall promptly deliver to the other copies of each such report filed with the
SEC.

                  SECTION 6.09. Control of Operations. Nothing contained in this
Agreement shall give CGI, directly or indirectly, the right to control or direct
the operations of STC and the STC Subsidiaries prior to the Effective Time.
Prior to the Effective Time, each of CGI and STC shall exercise, consistent with
the terms and conditions of this Agreement, complete control and supervision
over its respective operations.

                  SECTION 6.10. Further Action; Consents; Filings. Upon the
terms and subject to the conditions hereof, each of the parties hereto shall use
all reasonable efforts to (i) take, or cause to be taken, all appropriate
action, and do, or cause to be done, all things necessary, proper or advisable
under applicable Law or otherwise to consummate and make effective the Merger,
(ii) obtain from Governmental Entities any consents, licenses, permits, waivers,
approvals, authorizations or orders required to be obtained or made by CGI,
Merger Sub, STC or the Surviving Corporation or any of their respective
subsidiaries in connection with the authorization, execution and delivery of
this Agreement and the consummation of the Merger and (iii) make all necessary
filings, and thereafter make any other required or appropriate submissions, with
respect to this Agreement and the Merger required under (A) the rules and
regulations of the NASD, (B) the Securities Act, the Exchange Act and any other
applicable federal or state securities Laws, (C) the HSR Act, if any, and (D)
any other applicable Law. The parties hereto shall cooperate and consult with
each other in connection with the making of all such filings, including by
providing copies of all such documents to the nonfiling parties and their
advisors prior to filing, and none of the parties shall file any such document
if any of the other parties shall have reasonably objected to the filing of such
document. No party shall consent to any voluntary extension of any statutory
deadline or waiting period or to any voluntary delay of the consummation of the
Merger at the behest of any Governmental Entity without the consent and
agreement of the other parties hereto, which consent shall not be unreasonably
withheld or delayed.
<PAGE>   66
                                       47

                                   ARTICLE VII

                              ADDITIONAL AGREEMENTS

                  SECTION 7.01. Registration Statement; Joint Proxy Statement.
(a) As promptly as practicable after the execution of this Agreement, CGI and
STC shall jointly prepare and STC and CGI shall file with the SEC a document or
documents that will constitute (i) the prospectus forming part of the
registration statement on Form S-4 of CGI (together with all amendments thereto,
the "Registration Statement"), in connection with the registration under the
Securities Act of the CGI Common Stock to be issued to STC's stockholders
pursuant to the Merger and (ii) the Joint Proxy Statement with respect to the
Merger relating to the special meeting of each of STC's stockholders (the "STC
Stockholders' Meeting") and CGI's stockholders (the "CGI Stockholders' Meeting")
to be held to consider approval of this Agreement and the Merger contemplated
hereby (together with any amendments thereto, the "Joint Proxy Statement").
Copies of the Joint Proxy Statement shall be provided to the NASD in accordance
with its rules with respect to the NMS. Each of the parties hereto shall use all
reasonable efforts to cause the Registration Statement to become effective as
promptly as practicable after this date hereof, and, prior to the effective date
of the Registration Statement, the parties hereto shall take all action required
under any applicable Laws in connection with the issuance of shares of CGI
Common Stock pursuant to the Merger. CGI or STC, as the case may be, shall
furnish all information concerning itself as the other party may reasonably
request in connection with such actions and the preparation of the Registration
Statement and Joint Proxy Statement. As promptly as practicable after the
effective date of the Registration Statement, the Joint Proxy Statement shall be
mailed to the stockholders of CGI and STC. Each of the parties hereto shall
cause the Joint Proxy Statement to comply as to form and substance in all
material respects with the applicable requirements of (i) the Exchange Act, (ii)
the Securities Act, (iii) the rules and regulations of the NASD and (iv) the
General Corporation Law.

                  (b) The Joint Proxy Statement shall include (i) (A) subject to
the provisos contained in the first sentence of Section 6.06, the approval of
the Merger and the STC Amendment and recommendation of the board of directors of
STC to the stockholders of STC that they vote in favor of approval of this
Agreement and the Merger contemplated hereby and the STC Amendment, and (B) the
opinion of DLJ referred to in Section 4.18, and (ii) (A) subject to the provisos
contained in the first sentence of Section 6.06, the approval of the Merger and
the CGI Amendment and recommendation of the board of directors of CGI to the
stockholders of CGI that they vote in favor of approval of this Agreement and
the Merger contemplated hereby and the CGI Amendment, and (B) the opinion of
Lehman Brothers referred to in Section 5.18.

                  (c) No amendment or supplement to the Joint Proxy Statement 
or the Registration Statement shall be made without the approval of CGI and STC,
which approval
<PAGE>   67
                                       48

shall not be unreasonably withheld or delayed. Each of the parties hereto shall
advise the other parties hereto, promptly after it receives notice thereof, of
the time when the Registration Statement has become effective or any supplement
or amendment has been filed, of the issuance of any stop order, of the
suspension of the qualification of the CGI Common Stock issuable in connection
with the Merger for offering or sale in any jurisdiction, or of any request by
the SEC or the NASD for amendment of the Joint Proxy Statement or the
Registration Statement or comments thereon and responses thereto or requests by
the SEC for additional information.

                  (d) The information supplied by STC for inclusion in the
Registration Statement and the Joint Proxy Statement shall not, at (i) the time
the Registration Statement is filed with the SEC, (ii) if different, the time
the Registration Statement is declared effective, (iii) the time the Joint Proxy
Statement (or any amendment thereof or supplement thereto) is first mailed to
the stockholders of STC and CGI, (iv) the time of the STC Stockholders' Meeting,
(v) the time of the CGI Stockholders' Meeting and (vi) the Effective Time,
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 were made, not
misleading. If at any time prior to the Effective Time any event or circumstance
relating to STC or any STC Subsidiary, or their respective officers or
directors, should be discovered by STC that should be set forth in an amendment
or a supplement to the Registration Statement or Joint Proxy Statement, STC
shall promptly inform CGI. All documents that STC is responsible for filing with
the SEC in connection with the Merger will comply as to form in all material
respects with the applicable requirements of the rules and regulations of the
NASD, the General Corporation Law, the Securities Act and the Exchange Act.

                  (e) The information supplied by CGI for inclusion in the
Registration Statement and the Joint Proxy Statement shall not, at (i) the time
the Registration Statement is filed with the SEC, (ii) if different, the time
the Registration Statement is declared effective, (iii) the time the Joint Proxy
Statement (or any amendment thereof or supplement thereto) is first mailed to
the stockholders of CGI and STC, (iv) the time of the STC Stockholders' Meeting,
(v) the time of the CGI Stockholders' Meeting and (vi) the Effective Time,
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 were made, not
misleading. If, at any time prior to the Effective Time, any event or
circumstance relating to CGI or any CGI Subsidiary, or their respective officers
or directors, should be discovered by CGI that should be set forth in an
amendment or a supplement to the Registration Statement or Joint Proxy
Statement, CGI shall promptly inform STC. All documents that CGI is responsible
for filing with the SEC in connection with the Merger will comply as to form in
all material respects with the applicable requirements of the rules and
regulations of the NASD, the General Corporation Law, the Securities Act and the
Exchange Act.
<PAGE>   68
                                       49


                  SECTION 7.02. Stockholders' Meetings. STC shall call and hold
the STC Stockholders' Meeting and CGI shall call and hold the CGI Stockholders'
Meeting as promptly as practicable after the date hereof for the purpose of
voting upon the approval of this Agreement pursuant to the Joint Proxy Statement
and the Merger contemplated hereby, and each of CGI and STC shall use all
reasonable efforts to hold the CGI Stockholders' Meeting and the STC
Stockholders' Meeting on the same day and as soon as practicable after the date
on which the Registration Statement becomes effective. STC shall use all
reasonable efforts to solicit from its stockholders proxies in favor of the
approval of this Agreement and the Merger contemplated hereby and the Amendment
pursuant to the Joint Proxy Statement and shall take all other action necessary
or advisable to secure the vote or consent of stockholders required by the
General Corporation Law or applicable stock exchange requirements to obtain such
approval. CGI shall use all reasonable efforts to solicit from its stockholders
proxies in favor of the approval of this Agreement and the Merger contemplated
hereby pursuant to the Joint Proxy Statement, and shall take all other action
necessary or advisable to secure the vote or consent of stockholders required by
the General Corporation Law or applicable stock exchange requirements to obtain
such approval. Each of the parties hereto shall take all other action necessary
or, in the opinion of the other parties hereto, advisable to promptly and
expeditiously secure any vote or consent of stockholders required by applicable
Law and such party's certificate of incorporation and by-laws to effect the
Merger.

                  SECTION 7.03. Affiliates. (a) Not fewer than 45 days prior to
the Effective Time, STC shall deliver to CGI a list of names and addresses of
each person who was, in STC's reasonable judgment, at the record date for the
STC Stockholders' Meeting, an affiliate of STC. STC shall provide CGI such
information and documents as CGI shall reasonably request for purposes of
reviewing such list. STC shall use all reasonable efforts to deliver or cause to
be delivered to CGI, prior to the Effective Time, an affiliate agreement in the
form attached hereto as Exhibit 7.03(a) (each, an "STC Affiliate Agreement"),
executed by each of the affiliates of STC identified in the above-referenced
list. The foregoing notwithstanding, CGI shall be entitled to place legends as
specified in the form of STC Affiliate Agreement on the certificates evidencing
any of the CGI Common Stock to be received by (i) any affiliate of STC or (ii)
any person CGI reasonably identifies (by written notice to STC) as being a
person who may be deemed an "affiliate" within the meaning of Rule 145
promulgated under the Securities Act, and to issue appropriate stop transfer
instructions to the transfer agent for such CGI Common Stock, consistent with
the terms of the form of STC Affiliate Agreement, regardless of whether such
person has executed an STC Affiliate Agreement and regardless of whether such
person's name and address appear on Section 4.16 of the STC Disclosure Schedule.

                  (b) CGI shall use all reasonable efforts to obtain or cause to
be obtained, prior to the Effective Time, an affiliate agreement in the form
attached hereto as Exhibit 7.03(b) (each, a "CGI Affiliate Agreement"), executed
by each person who was, in CGI's
<PAGE>   69
                                       50

reasonable judgment, at the record date for the CGI Stockholders' Meeting, an
affiliate of CGI.

                  SECTION 7.04. Directors' and Officers' Indemnification and
Insurance. (a) The certificate of incorporation and by-laws of the Surviving
Corporation shall contain provisions no less favorable with respect to
indemnification than are set forth in the certificate of incorporation and
by-laws of STC on the date hereof, which provisions shall not be amended,
repealed or otherwise modified for a period of six years from the Effective Time
in any manner that would affect adversely the rights thereunder of individuals
who at the Effective Time were directors, officers, employees, fiduciaries or
agents of STC, unless such modification shall be required by law.

                  (b) STC shall, to the fullest extent permitted under
applicable law and regardless of whether the Merger shall become effective,
indemnify and hold harmless, and, after the Effective Time, the Surviving
Corporation shall, to the fullest extent permitted under applicable law,
indemnify and hold harmless, each present and former director, officer,
employee, fiduciary and agent of STC and each STC Subsidiary (collectively, the
"Indemnified Parties") against all costs and expenses (including attorneys'
fees), judgments, fines, losses, claims, damages, liabilities and settlement
amounts paid in connection with any claim, action, suit, proceeding or
investigation (whether arising before or after the Effective Time), whether
civil, criminal, administrative or investigative, arising out of or pertaining
to any action or omission in their capacity as an officer, director, employee,
fiduciary or agent, whether occurring before or after the Effective Time, for a
period of six years after the date hereof. In the event of any such claim,
action, suit, proceeding or investigation, (i) STC or the Surviving Corporation,
as the case may be, shall pay the reasonable fees and expenses of counsel
selected by the Indemnified Parties, which counsel shall be reasonably
satisfactory to STC or the Surviving Corporation, promptly after statements
therefor are received and (ii) STC and the Surviving Corporation shall cooperate
in the defense of any such matter; provided, however, that neither STC nor the
Surviving Corporation shall be liable for any settlement effected without its
written consent (which consent shall not be unreasonably withheld); provided
further that neither STC nor the Surviving Corporation shall be obligated
pursuant to this Section 7.04(b) to pay the fees and expenses of more than one
counsel for all Indemnified Parties in any single action; provided further that,
in the event that any claim for indemnification is asserted or made within such
six-year period, all rights to indemnification in respect of such claim shall
continue until the disposition of such claim.

                  (c) The Surviving Corporation shall use all reasonable efforts
to maintain in effect for three years from the Effective Time, if available, the
current directors' and officers' liability insurance policies maintained by STC
(provided that the Surviving Corporation may substitute therefor policies of at
least the same coverage containing terms and conditions which are not materially
less favorable) with respect to matters occurring prior to the Effective Time;
provided, however, that in no event shall the Surviving
<PAGE>   70
                                       51

Corporation be required to expend pursuant to this Section 7.04(c) more than an
amount per year equal to 125% of current annual premiums paid by STC for such
insurance.

                  (d) In the event STC or the Surviving Corporation or any of
their respective successors or assigns (i) consolidates with or merges into any
other person and shall not be the continuing or surviving corporation or entity
of such consolidation or merger or (ii) transfers all or substantially all of
its properties and assets to any person, then, and in each such case, proper
provision shall be made so that the successors and assigns of STC or the
Surviving Corporation, as the case may be, or at CGI's option, CGI, shall assume
the obligations set forth in this Section 7.04.

                  SECTION 7.05. No Shelf Registration. CGI shall not be required
to amend or maintain the effectiveness of the Registration Statement for the
purpose of permitting resale of the shares of CGI Common Stock received pursuant
hereto by the persons who may be deemed to be "affiliates" of STC or CGI within
the meaning of Rule 145 promulgated under the Securities Act.

                  SECTION 7.06. Public Announcements. The initial press release
concerning the Merger shall be a joint press release and, thereafter, CGI and
STC shall consult with each other before issuing any press release or otherwise
making any public statements with respect to this Agreement or the Merger and
shall not issue any such press release or make any such public statement without
the prior written approval of the other, except to the extent required by
applicable Law or the requirements of the rules and regulations of the NASD, in
which case the issuing party shall use all reasonable efforts to consult with
the other party before issuing any such release or making any such public
statement.

                  SECTION 7.07.  Officers and Directors of CGI.  (a)  At the 
Effective Time, subject to the certificate of incorporation and by-laws of CGI,
Stephen A. Sherwin, M.D. shall continue to hold the offices of Chairman,
President and Chief Executive Officer of CGI.

                  (b) Immediately after the Effective Time, the total number of
persons serving on the board of directors of CGI shall be nine (unless otherwise
agreed in writing by STC and CGI prior to the Effective Time), and shall consist
of the following individuals:

                  David W. Carter
                  James M. Gower
                  Raju S. Kucherlapati, Ph.D.
                  Joseph E. Maroun
                  John T. Potts, Jr., M.D.
                  Thomas E. Shenk, Ph.D.
                  Stephen A. Sherwin, M.D.
<PAGE>   71
                                       52

                  Eugene L. Step
                  Inder M. Verma, Ph.D.

In the event that, prior to the Effective Time, any person so selected to serve
on the board of directors of CGI is unable or unwilling to serve in such
position, the party with which such person was affiliated prior to the date
hereof shall designate another person to serve in such person's stead in
accordance with the provisions of the immediately preceding sentence; provided
that any such designee shall be reasonably satisfactory to each of CGI and STC.
From and after the Effective Time, the composition of the board of directors
shall be determined in accordance with the certificate of incorporation and
by-laws of CGI.

                  SECTION 7.08. NMS Listing. Each of the parties hereto shall
use all reasonable efforts to obtain, prior to the Effective Time, the approval
for listing on the NMS, effective upon official notice of issuance, of the
shares of CGI Common Stock into which the shares of STC Capital Stock will be
converted pursuant to Article III.

                  SECTION 7.09. Blue Sky. Each of the parties hereto shall use
all reasonable efforts to obtain, prior to the Effective Time, all necessary
blue sky permits and approvals required under Blue Sky Laws to permit the
distribution of the shares of CGI Common Stock to be issued in accordance with
the provisions of this Agreement.

                  SECTION 7.10. STC Stock Options. At the Effective Time, CGI
shall assume, by virtue of this Agreement and without any further action on the
part of STC, all of STC's obligations with respect to each outstanding STC Stock
Option, whether vested or unvested. STC shall take all corporate action
necessary to ensure that, unless otherwise elected by CGI prior to the Effective
Time, CGI shall make such assumption in such manner that CGI (i) is a
corporation "assuming a stock option in a transaction to which Section 424(a)
applies" within the meaning of Section 424 of the Code or (ii) to the extent
that Section 424 of the Code does not apply to such STC Stock Option, would be
such a corporation were Section 424 of the Code applicable to such STC Stock
Option; and, if not so otherwise elected, after the Effective Time, all
references to STC in the STC Stock Plans and the applicable STC Stock Option
agreements shall be deemed to refer to CGI, which shall have assumed the STC
Stock Plans as of the Effective Time by virtue of this Agreement and without any
further action on the part of STC or CGI. Each STC Stock Option so assumed by
CGI under this Agreement shall continue to have, and be subject to, the same
terms and conditions set forth in the applicable STC Stock Plan and the
applicable STC Stock Option as in effect immediately prior to the Effective
Time, except as otherwise provided in Section 3.05. CGI shall use all reasonable
efforts to ensure that the STC Stock Options intended to qualify as incentive
stock options under Section 422 of the Code prior to the Effective Time continue
to so qualify after the Effective Time. As soon as practicable after the
Effective Time, CGI shall file with the SEC and use its best efforts to have
declared
<PAGE>   72
                                       53

effective a registration statement on Form S-8 with respect to the shares of CGI
Common Stock issuable under the assumed STC Stock Plans.

                  SECTION 7.11.  [INTENTIONALLY LEFT BLANK]

                  SECTION 7.12.  Bridge Facility.  (a)  Pursuant to Section
6.01(b), STC is prohibited from, among other things, exercising the Fletcher Put
Options.

                  (b) During the term of this Agreement, STC shall promptly
notify CGI if the Projected Cash Balances are (i) then forecast by senior
management of STC to fall below $5,000,000 within 30 days or (ii) then below
$5,000,000. Such notice (a "Liquidity Notice") shall include, without
limitation, the date on which the Projected Cash Balances are forecast to fall
below $5,000,000. STC shall use all reasonable efforts to prevent the Actual
Balances from falling below $5,000,000. At CGI's request, STC shall borrow under
the Bridge Facility to prevent the Actual Balances from falling below $5,000,000
if sufficient funds for such purpose are not available to STC in connection with
one or more Liquidity Takedowns; provided, however, that if STC is required by
CGI to borrow under this Section 7.12, then CGI shall not have the option
pursuant to Section 1(c) of the license agreement related to the Bridge Facility
Promissory Note to forgive in full the Advances and activate such license
agreement.

                  (c) Upon receipt of a Liquidity Notice from STC and so long as
a Commitment Termination Event shall not have occurred, if so requested by STC,
CGI shall lend STC funds under the Bridge Facility as provided in subsection (d)
of this Section 7.12 in amounts sufficient to prevent the Projected Cash
Balances from falling below $5,000,000. All funds provided to STC under the
Bridge Facility shall be used solely to fund ordinary and necessary operating
expenses in accordance with the then current Operating Budget.

                  (d) In the event that STC elects to borrow funds pursuant to
subsection (c) of this Section 7.12 and provided that no Commitment Termination
Event shall have occurred, CGI shall, upon the terms and subject to the
conditions set forth herein and in the Bridge Facility Promissory Note, make
advances (the "Advances") to STC from time to time on any business day during
the period from the date hereof through the earlier to occur of June 30, 1997
and any Commitment Termination Event in an aggregate principal amount not to
exceed at any time outstanding $5,000,000. Each Advance shall be in an amount
not less than $50,000 or an integral multiple of $25,000 in excess thereof. Each
Advance shall be made upon notice (which notice may be included in a Liquidity
Notice) given by STC to CGI not later than 11:00 a.m. San Francisco time on the
second business day prior to the date of the proposed Advance. Such notice shall
specify the date and amount of the proposed Advance. Not later than 2:00 p.m.
San Francisco time on the date of such Advance and upon fulfillment of the
applicable conditions set forth in subsection (e) of this Section 7.12,
<PAGE>   73
                                       54

CGI shall make such Advance available to STC in same day funds at CGI's address
specified above.

                  (e) (i) The obligation of CGI to make its initial Advance
under the Bridge Facility shall be subject to the condition precedent that CGI
shall have received, on or before the day of such initial Advance, a certificate
of the Secretary or an Assistant Secretary of STC dated the day of such initial
Advance, in form and substance satisfactory to CGI, certifying (A) copies of the
resolutions of the board of directors of STC approving the Bridge Facility
Promissory Note, and of all documents evidencing other necessary corporate
action and governmental approvals, if any, with respect to the Bridge Facility
Promissory Note, and (B) the names and true signatures of the officers of STC
authorized to sign the Bridge Facility Promissory Note and the other documents
to be delivered hereunder.

         (ii) The obligation of CGI to make each Advance (including the initial
Advance) shall be subject to the further conditions precedent that (A) this
Agreement shall have been executed and delivered by the parties hereto and shall
be in full force and effect; (B) the representations and warranties contained in
the Bridge Facility Promissory Note shall be, and CGI shall have received a
certificate signed by a duly authorized officer of STC, dated the date of such
Advance, certifying that such representations and warranties are, true, complete
and correct in all material respects on and as of the date of such Advance,
before and after giving effect to such Advance and to the application of the
proceeds therefrom, as though made on and as of such date; (C) no event shall
have occurred and be continuing, or be reasonably likely to result from such
Advance or from the application of the proceeds therefrom, which constitutes an
Event of Default or would constitute an Event of Default but for the requirement
that notice be given or time elapse or both; and (D) CGI shall have received a
certificate signed by a duly authorized officer of STC, dated the date of such
Advance, certifying the then Projected Cash Balances and Actual Cash Balances.

                  (f) STC shall, in consultation with the Steering Committee,
revise the Projected Cash Balances and the Operating Budget from time to time,
but in no event less frequently than monthly; provided, however, that in the
event STC delivers to CGI a revised Operating Budget materially adversely
different than the Operating Budget delivered on the date hereof without the
prior written consent of CGI, CGI's obligations under the Bridge Facility shall
be suspended until such time as the parties hereto agree to a revised Operating
Budget.

                  SECTION 7.13. Audited Financial Statements. As soon as
practicable after the date hereof or, in the case of the fiscal quarter of STC
ending March 31, 1997, as soon as practicable after March 31, 1997 if CGI does
not then reasonably expect the Effective Time to occur within 45 days of such
date, STC shall cause its independent certified public accountants to prepare
and audit balance sheets of STC at and as of December 31, 1996 and March 31,
1997, respectively, and related statements of income, retained earnings,
<PAGE>   74
                                       55

shareholders' equity and changes in financial position of STC for the six-month
period ended December 31, 1996 and the nine-month period ending March 31, 1997,
respectively, and to render its unqualified report thereon. Within one business
day of receipt of the above described audited consolidated financial statements
of STC, STC shall deliver to CGI true, complete and correct copies of such
financial statements, together with the auditor's reports thereon.

                  SECTION 7.14. Liquidity Takedowns; Additional Debt. (a)
Notwithstanding the restrictions contained in Section 6.01 and the provisions of
the Bridge Facility referred to in Section 7.12, STC may issue additional shares
of STC Capital Stock (including pursuant to the Fletcher Put Options) if, and
only if, the following conditions shall have been satisfied to the reasonable
satisfaction of CGI on or prior to the date of issuance of such shares of STC
Capital Stock (a transaction meeting all of the following conditions being
referred to as a "Liquidity Takedown"):

                           (i) STC shall have given CGI not fewer than two
         business days' notice of its intention to enter into an agreement to
         sell any STC Capital Stock;

                           (ii) such sale shall be made only by a private 
         placement to 10 or fewer "accredited investors";

                           (iii) such accredited investor(s) shall have received
         a copy of the Registration Statement and Joint Proxy Statement (or the
         most recent version thereof filed with the SEC);

                           (iv) any shares of STC Capital Stock so issued will,
         by their terms, be converted into shares of CGI Common Stock pursuant
         to the Merger;

                           (v) such accredited investor(s) shall have delivered
         to CGI and STC an irrevocable proxy to vote all shares of STC Capital
         Stock held thereby in favor of the Merger; and

                           (vi) the other terms and conditions thereof shall be
         reasonably satisfactory to CGI; provided that any term that creates any
         right whatsoever in any asset or property of STC, or any ongoing
         obligation or liability on STC or CGI after consummation of the Merger,
         shall be conclusively not satisfactory; provided further that
         contractual obligations with respect to the Fletcher Put Options in
         existence on the date hereof shall be deemed reasonable.

                  (b) Notwithstanding the restrictions contained in Section 6.01
and the provisions of the Bridge Facility referred to in Section 7.12, STC may
incur indebtedness in addition to that in effect on the date hereof in a
principal amount not in excess of $2,000,000
<PAGE>   75
                                       56

if, and only if, the following conditions shall have been satisfied to the
reasonable satisfaction of CGI on or prior to the date of incurrence of such
additional indebtedness (a transaction meeting all of the following conditions
being referred to as a "PERMITTED FINANCING"):

                           (i) STC shall have given CGI not fewer than two
         business days' notice of its intention to enter into an agreement to
         incur any additional indebtedness;

                           (ii) such additional indebtedness shall be unsecured;

                           (iii) any shares of STC Capital Stock (or warrants,
         options or similar securities convertible into or exchangeable for STC
         Capital Stock) issued in connection with such additional indebtedness
         will, by their terms, be converted into shares of CGI Common Stock
         pursuant to the Merger; and

                           (iv) the other terms and conditions thereof shall be
         reasonably satisfactory to CGI; provided that any term that creates any
         right whatsoever in any asset or property of STC, or any ongoing
         obligation or liability on STC or CGI after repayment in full of such
         additional indebtedness, shall be conclusively not satisfactory.

                  (c) All funds provided to STC under any Liquidity Takedown or
Permitted Financing shall be used solely to fund ordinary and necessary
operating expenses in accordance with the then current Operating Budget.

                  SECTION 7.15. Collateralization. Promptly after the date
hereof, the parties hereto shall meet and negotiate in good faith towards
securing the Bridge Facility Promissory Note with the assets referred to in the
license agreement related thereto in the circumstances where STC is required to
borrow under Section 7.12(b). Such good faith negotiations shall involve
negotiating a customary security interest and security agreement. CGI and STC
shall use all reasonable efforts to conclude such negotiations by January 31,
1997.


                                  ARTICLE VIII

                            CONDITIONS TO THE MERGER

                  SECTION 8.01. Conditions to the Obligations of Each Party to
Consummate the Merger. The obligations of the parties hereto to consummate the
Merger, or to permit the consummation of the Merger, are subject to the
satisfaction or, if permitted by applicable Law, waiver of the following
conditions:
<PAGE>   76
                                       57

                           (a) the Registration Statement shall have been
         declared effective by the SEC under the Securities Act and no stop
         order suspending the effectiveness of the Registration Statement shall
         have been issued by the SEC and no proceeding for that purpose shall
         have been initiated by the SEC and not concluded or withdrawn;

                           (b) (i) this Agreement and the Merger shall have been
         duly approved by the requisite vote of the stockholders of each of STC
         and CGI and (ii) the CGI Amendment shall have been duly approved by the
         requisite vote of the stockholders of CGI, in each case in accordance
         with the General Corporation Law;

                           (c) no court of competent jurisdiction shall have
         issued or entered any order, writ, injunction or decree, and no other
         Governmental Entity shall have issued any order, which is then in
         effect and has the effect of making the Merger illegal or otherwise
         prohibiting its consummation;

                           (d) any waiting period (and any extension thereof)
         applicable to the consummation of the Merger under the HSR Act or any
         other applicable competition, merger control or similar Law shall have
         expired or been terminated;

                           (e) all consents, approvals and authorizations
         legally required to be obtained to consummate the Merger shall have
         been obtained from all Governmental Entities, except where the failure
         to obtain any such consent, approval or authorization could not
         reasonably be expected to result in a change in or have an effect on
         the business of STC or CGI that is materially adverse to the business,
         assets (including intangible assets), liabilities (contingent or
         otherwise), condition (financial or otherwise) or results of operations
         of CGI and its subsidiaries, taken as a whole; and

                           (f) the shares of CGI Common Stock into which the
         shares of STC Capital Stock will be converted pursuant to Article III
         and the shares of CGI Common Stock issuable upon the exercise of
         options pursuant to Section 3.05 shall have been authorized for listing
         on the NMS, subject to official notice of issuance.

                  SECTION 8.02. Conditions to the Obligations of STC. The
obligations of STC to consummate the Merger, or to permit the consummation of
the Merger, are subject to the satisfaction or, if permitted by applicable Law,
waiver of the following further conditions:

                           (a) each of the representations and warranties of CGI
         contained in this Agreement that is qualified by materiality shall be
         true, complete and correct at and as of the Effective Time as if made
         at and as of such time (other than representations and warranties which
         address matters only as of a certain date which
<PAGE>   77
                                       58

         shall be true, complete and correct as of such certain date) and each
         of the representations and warranties that is not so qualified shall be
         true, complete and correct in all material respects at and as of the
         Effective Time as if made at and as of such time (other than
         representations and warranties which address matters only as of a
         certain date which shall be true, complete and correct in all material
         respects as of such certain date), in each case except as contemplated
         or permitted by this Agreement, and STC shall have received a
         certificate of the Chairman or President and Chief Financial Officer of
         CGI to such effect;

                           (b) CGI shall have performed or complied in all
         material respects with all material agreements and covenants required
         by this Agreement to be performed or complied with by it on or prior to
         the Effective Time and STC shall have received a certificate of the
         Chairman or President and Chief Financial Officer of CGI to that
         effect; and

                           (c) Brobeck, Phleger & Harrison, special counsel to
         STC, shall have issued its opinion, such opinion dated on or about the
         date of the Closing, addressed to STC, and reasonably satisfactory to
         it, based upon customary representations of STC and customary
         assumptions (including delivery and non- withdrawal of the opinion
         referred to in subsection (c) of Section 8.03), to the effect that the
         Merger will be treated for federal income tax purposes as a
         reorganization qualifying under the provisions of Section 368 of the
         Code and that each of STC, Merger Sub and CGI will be a party to the
         reorganization within the meaning of Section 368(b) of the Code, which
         opinions shall not have been withdrawn or modified in any material
         respect.

                  SECTION 8.03. Conditions to the Obligations of CGI. The
obligations of CGI to consummate the Merger, or to permit the consummation of
the Merger, are subject to the satisfaction or, if permitted by applicable Law,
waiver of the following further conditions:

                           (a) each of the representations and warranties of STC
         contained in this Agreement that is qualified by materiality shall be
         true, complete and correct at and as of the Effective Time as if made
         at and as of such time (other than representations and warranties which
         address matters only as of a certain date which shall be true, complete
         and correct as of such certain date) and each of the representations
         and warranties that is not so qualified shall be true, complete and
         correct in all material respects at and as of the Effective Time as if
         made at and as of such time (other than representations and warranties
         which address matters only as of a certain date which shall be true,
         complete and correct in all material respects as of such certain date),
         in each case except as contemplated or permitted by this
<PAGE>   78
                                       59

         Agreement, and CGI shall have received a certificate of the Chairman or
         President and Chief Financial Officer of STC to such effect;

                           (b) STC shall have performed or complied in all
         material respects with all material agreements and covenants required
         by this Agreement to be performed or complied with by it on or prior to
         the Effective Time and CGI shall have received a certificate of the
         Chairman or President and Chief Financial Officer of STC to that
         effect;

                           (c) Shearman & Sterling, special counsel to CGI,
         shall have issued its opinion, such opinion dated on or about the date
         of the Closing, addressed to CGI, and reasonably satisfactory to it,
         based upon customary representations of CGI and customary assumptions
         (including delivery and non-withdrawal of the opinion referred to in
         subsection (c) of Section 8.02), to the effect that the Merger will be
         treated for federal income tax purposes as a reorganization qualifying
         under the provisions of Section 368 of the Code and that each of CGI,
         Merger Sub and STC will be a party to the reorganization within the
         meaning of Section 368(b) of the Code, which opinions shall not have
         been withdrawn or modified in any material respect;

                           (d) the STC Amendment shall have been duly approved 
         by the requisite vote of the stockholders of STC in accordance with the
         General Corporation Law;

                           (e) STC shall have executed and delivered the Bridge
         Facility Promissory Note and the license agreement referred to therein;
         and

                           (f) the holder(s) of the Fletcher Warrant shall have
         elected pursuant to the Fletcher Notice and in accordance with Section
         10 of the Fletcher Warrant either (i) to resell the Fletcher Warrant to
         STC for cash or (ii) to permit CGI to assume the Fletcher Warrant
         pursuant to Section 3.05; provided, however, that any disagreement
         between STC and Fletcher as to the cash amount so required to be paid
         shall not constitute a failure of this condition.


                                   ARTICLE IX

                        TERMINATION, AMENDMENT AND WAIVER

                  SECTION 9.01.  Termination.  This Agreement may be terminated
and the Merger may be abandoned at any time prior to the Effective Time,
notwithstanding any requisite adoption and approval of this Agreement, as
follows:
<PAGE>   79
                                       60

                           (a) by mutual written consent duly authorized by the
         boards of directors of each of CGI and STC;

                           (b) by either CGI or STC, if the Effective Time shall
         not have occurred on or before August 31, 1997; provided, however, that
         the right to terminate this Agreement under this Section 9.01(b) shall
         not be available to any party whose failure to fulfill any obligation
         under this Agreement shall have caused, or resulted in, the failure of
         the Effective Time to occur on or before such date;

                           (c) by either CGI or STC, if any Governmental Order,
         writ, injunction or decree preventing the consummation of the Merger
         shall have been entered by any court of competent jurisdiction and
         shall have become final and nonappealable;

                           (d) by CGI, if (i) the board of directors of STC
         withdraws, modifies or changes its recommendation of this Agreement,
         the Merger or the Amendment in a manner adverse to CGI or its
         stockholders or shall have resolved to do so, (ii) the board of
         directors of STC shall have recommended to the stockholders of STC a
         Competing Transaction or shall have resolved to do so or (iii) a tender
         offer or exchange offer for 15 percent or more of the outstanding
         shares of capital stock of STC shall have been commenced and the board
         of directors of STC shall have failed to recommend against acceptance
         of such tender offer or exchange offer by its stockholders (including
         by taking no position with respect to the acceptance of such tender
         offer or exchange offer by its stockholders);

                           (e) by STC, if (i) the board of directors of CGI
         withdraws, modifies or changes its recommendation of this Agreement or
         the Merger in a manner adverse to STC or its stockholders or shall have
         resolved to do so, (ii) the board of directors of CGI shall have
         recommended to the stockholders of CGI a Competing Transaction or shall
         have resolved to do so or (iii) a tender offer or exchange offer for 15
         percent or more of the outstanding shares of capital stock of CGI shall
         have been commenced and the board of directors of CGI shall have failed
         to recommend against acceptance of such tender offer or exchange offer
         by its stockholders (including by taking no position with respect to
         the acceptance of such tender offer or exchange offer by its
         stockholders);

                           (f) by CGI or STC, if (i) this Agreement and the
         Merger shall fail to receive the requisite votes for approval at the
         STC Stockholders' Meeting or any adjournment or postponement thereof or
         (ii) if this Agreement and the Merger shall fail to receive the
         requisite votes for approval at the CGI Stockholders' Meeting or any
         adjournment or postponement thereof;
<PAGE>   80
                                       61

                           (g) by CGI, upon a breach of any representation,
         warranty, covenant or agreement on the part of STC set forth in this
         Agreement, or if any representation or warranty of STC shall have
         become untrue, incomplete or incorrect, in either case such that the
         conditions set forth in Section 8.03 would not be satisfied (a
         "TERMINATING STC BREACH"); provided, however, that, if such Terminating
         STC Breach is curable by STC through the exercise of its reasonable
         efforts within 60 days and for so long as STC continues to exercise
         such reasonable efforts, CGI may not terminate this Agreement under
         this Section 9.01(g); and provided further that the preceding proviso
         shall not in any event be deemed to extend any date set forth in
         paragraph (b) of this Section 9.01;

                           (h) by STC, upon breach of any representation,
         warranty, covenant or agreement on the part of CGI set forth in this
         Agreement, or if any representation or warranty of CGI shall have
         become untrue, incomplete or incorrect, in either case such that the
         conditions set forth in Section 8.02 would not be satisfied (a
         "TERMINATING CGI BREACH"); provided, however, that, if such Terminating
         CGI Breach is curable by CGI through the exercise of its reasonable
         efforts within 60 days and for so long as CGI continues to exercise
         such reasonable efforts, STC may not terminate this Agreement under
         this Section 9.01(h); and provided further that the preceding proviso
         shall not in any event be deemed to extend any date set forth in
         paragraph (b) of this Section 9.01;

                           (i) by STC, if (A) the board of directors of STC
         shall have resolved to accept, accepted or recommended to the
         shareholders of STC, a Superior Proposal, and (B) in the case of the
         termination of this Agreement under this Section 9.01(i) by STC, STC
         shall have paid to CGI all amounts owing by STC to CGI under Section
         9.05(b); and

                           (j) by CGI, if (A) the board of directors of CGI
         shall have resolved to accept, accepted or recommended to the
         shareholders of CGI, a Superior Proposal, and (B) in the case of the
         termination of this Agreement under this Section 9.01(j) by CGI, CGI
         shall have paid to STC all amounts owing by CGI to STC under Section
         9.05(c).

                  SECTION 9.02. Effect of Termination. Except as provided in
Section 9.05, in the event of termination of this Agreement pursuant to Section
9.01, this Agreement shall forthwith become void, there shall be no liability
under this Agreement on the part of CGI or STC or any of their respective
officers or directors, and all rights and obligations of each party hereto shall
cease, subject to the remedies of the parties hereto set forth in Section
9.05(b), (c), (d) and (e); provided, however, that nothing herein shall relieve
any party hereto from liability for the willful or intentional breach of any of
its representations and warranties or the willful or intentional breach of any
of its covenants or agreements set forth in this Agreement.
<PAGE>   81
                                       62


                  SECTION 9.03. Amendment. This Agreement may be amended by the
parties hereto by action taken by or on behalf of their respective boards of
directors at any time prior to the Effective Time; provided, however, that,
after the approval of this Agreement by the stockholders of STC or CGI, as the
case may be, no amendment may be made, except such amendments as have received
the requisite stockholder approval and such amendments as are permitted to be
made without stockholder approval under the General Corporation Law. This
Agreement may not be amended except by an instrument in writing signed by the
parties hereto.

                  SECTION 9.04. Waiver. At any time prior to the Effective Time,
any party hereto may (a) extend the time for or waive compliance with the
performance of any obligation or other act of any other party hereto or (b)
waive any inaccuracy in the representations and warranties contained herein or
in any document delivered pursuant hereto. Any such extension or waiver shall be
valid if set forth in an instrument in writing signed by the party or parties to
be bound thereby.

                  SECTION 9.05. Expenses. (a) Except as set forth in this
Section 9.05, all Expenses incurred in connection with this Agreement, the STC
Stock Option Agreement, the CGI Stock Option Agreement and the Merger shall be
paid by the party incurring such Expenses, whether or not the Merger is
consummated, except that CGI and STC each shall pay one-half of all Expenses
incurred solely for printing, filing and mailing the Registration Statement and
the Joint Proxy Statement and all SEC and other regulatory filing fees incurred
in connection with the Registration Statement and the Joint Proxy Statement and
any fees required to be paid under the HSR Act.

                  (b) In the event that CGI shall terminate this Agreement
pursuant to Section 9.01(d), (f)(i) or (g), or STC shall terminate this
Agreement pursuant to Section 9.01(f)(i) or (i), then STC shall pay to CGI an
amount equal to $3,000,000 plus all of CGI's Expenses.

                  (c) In the event that STC shall terminate this Agreement
pursuant to Section 9.01(e), (f)(ii) or (h) or CGI shall terminate this
Agreement pursuant to Section 9.01(f)(ii) or (j), CGI shall pay to STC an amount
equal to $3,000,000 plus all of STC's Expenses.

                  (d) Any payment required to be made pursuant to Section
9.05(b) or (c) shall be made to the party entitled to receive such payment not
later than two business days after delivery to the other party of notice of
demand for payment and shall be made by wire transfer of immediately available
funds to an account designated by the party entitled to receive payment in the
notice of demand for payment delivered pursuant to this Section 9.05(d);
provided, however, that, in the event both CGI and STC would otherwise be
entitled to payments under this Section 9.05 in connection with the termination
of this
<PAGE>   82
                                       63

Agreement pursuant to both Sections 9.01(f)(i) and (f)(ii), neither party shall
be required to make any payment under this Section 9.05.

                  (e) In the event that CGI or STC, as the case may be, shall
fail timely to make any payment on Expense reimbursement required to be made
pursuant to Section 9.05(b) or (c), the amount of any such required payment on
Expense reimbursement shall be increased to include the costs and expenses
actually incurred or accrued by the other (including, without limitation, fees
and expenses of counsel) in connection with the collection under and enforcement
of this Section 9.05, together with interest on such unpaid Expense
reimbursement, commencing on the date that such Expense reimbursement became
due, at a rate equal to the rate of interest publicly announced by Citibank,
N.A., from time to time, in The City of New York, from time to time, as such
bank's base rate plus 3.00 percent per annum.


                                    ARTICLE X

                               GENERAL PROVISIONS

                  SECTION 10.01. Non-Survival of Representations and Warranties.
The representations and warranties in this Agreement shall terminate at the
Effective Time or upon the termination of this Agreement pursuant to Section
9.01, as the case may be. Each party agrees that, except for the representations
and warranties contained in this Agreement and the CGI Disclosure Schedule and
the STC Disclosure Schedule, no party hereto has made any other representations
and warranties, and each party hereby disclaims any other representations and
warranties made by itself or any of its officers, directors, employees, agents,
financial and legal advisors or other representatives, with respect to the
execution and delivery of this Agreement or the Merger contemplated herein,
notwithstanding the delivery or disclosure to any other party or any party's
representatives of any documentation or other information with respect to any
one or more of the foregoing.

                  SECTION 10.02. Notices. All notices, requests, claims, demands
and other communications hereunder shall be in writing and shall be given (and
shall be deemed to have been duly given upon receipt) by delivery in person, by
telecopy or facsimile, by registered or certified mail (postage prepaid, return
receipt requested) or by a nationally recognized courier service to the
respective parties at their addresses set forth on the signature pages to this
Agreement (or at such other address for a party as shall be specified in a
notice given in accordance with this Section 10.02).

                  SECTION 10.03. Severability. If any term or other provision of
this Agreement is invalid, illegal or incapable of being enforced by any rule of
Law or public policy, all other conditions and provisions of this Agreement
shall nevertheless remain in full force and effect so long as the economic or
legal substance of the Merger is not affected in
<PAGE>   83
                                       64

any manner materially adverse to any party. Upon such determination that any
term or other provision is invalid, illegal or incapable of being enforced, the
parties hereto shall negotiate in good faith to modify this Agreement so as to
effect the original intent of the parties as closely as possible in a mutually
acceptable manner to the fullest extent permitted by applicable Law in order
that the Merger may be consummated as originally contemplated to the fullest
extent possible.

                  SECTION 10.04. Assignment; Binding Effect; Benefit. Neither
this Agreement nor any of the rights, interests or obligations hereunder shall
be assigned by any of the parties hereto (whether by operation of Law or
otherwise) without the prior written consent of the other parties hereto.
Subject to the preceding sentence, this Agreement shall be binding upon and
shall inure to the benefit of the parties hereto and their respective successors
and permitted assigns. Notwithstanding anything contained in this Agreement to
the contrary, other than Section 7.06, nothing in this Agreement, expressed or
implied, is intended to confer on any person other than the parties hereto or
their respective successors and permitted assigns any rights or remedies under
or by reason of this Agreement.

                  SECTION 10.05. Incorporation of Exhibits. The CGI Disclosure
Schedule, the STC Disclosure Schedule and all Exhibits attached hereto and
referred to herein are hereby incorporated herein and made a part of this
Agreement for all purposes as if fully set forth herein.

                  SECTION 10.06. Specific Performance. The parties hereto agree
that irreparable damage would occur in the event any provision of this Agreement
were not performed in accordance with the terms hereof and that the parties
shall be entitled to specific performance of the terms hereof, in addition to
any other remedy at law or in equity.

                  SECTION 10.07.  Governing Law.  THIS AGREEMENT SHALL BE
GOVERNED BY, AND CONSTRUED AND ENFORCED IN ACCORDANCE WITH, THE LAWS OF THE
STATE OF DELAWARE, WITHOUT REGARD TO PRINCIPLES OF CONFLICT OF LAWS.

                  SECTION 10.08. Waiver of Jury Trial. EACH PARTY HERETO HEREBY
IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY PROCEEDING (WHETHER BASED
ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR RELATING TO THIS AGREEMENT OR
ANY TRANSACTION OR AGREEMENT CONTEMPLATED HEREBY OR THE ACTIONS OF ANY PARTY
HERETO IN THE NEGOTIATION, ADMINISTRATION, PERFORMANCE OR ENFORCEMENT HEREOF.

                  SECTION 10.09.  Headings.  The descriptive headings contained
in this Agreement are included for convenience of reference only and shall not
affect in any way the meaning or interpretation of this Agreement.
<PAGE>   84
                                       65

                  SECTION 10.10. Counterparts. This Agreement may be executed
and delivered (including by facsimile transmission) in one or more counterparts,
and by the different parties hereto in separate counterparts, each of which when
executed and delivered shall be deemed to be an original but all of which taken
together shall constitute one and the same agreement.

                  SECTION 10.11. Entire Agreement. This Agreement (including the
Exhibits, the CGI Disclosure Schedule and the STC Disclosure Schedule), the STC
Stock Option Agreement and the CGI Stock Option Agreement constitute the entire
agreement among the parties with respect to the subject matter hereof and
supersede all prior agreements and understandings among the parties with respect
thereto. No addition to or modification of any provision of this Agreement shall
be binding upon any party hereto unless made in writing and signed by all
parties hereto.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   85
                  IN WITNESS WHEREOF, the parties hereto have caused this
Agreement to be executed as of the date first written above by their respective
officers thereunto duly authorized.


                                     CELL GENESYS, INC.


                                     By:   \s\ STEPHEN A. SHERWIN
                                          ______________________________________
                                          Stephen A. Sherwin, M.D.
                                          Chairman of the Board, President and
                                               Chief Executive Officer

                                     322 Lakeside Drive
                                     Foster City, California  94404
                                     Telephone:  (415) 358-9600
                                     Telecopy:  (415) 358-0230
                                     Attention:  Kathleen Sereda Glaub

                                     with a copy to:

                                     Shearman & Sterling
                                     555 California Street
                                     San Francisco, California  94104-1522
                                     Telephone:  (415) 616-1100
                                     Telecopy:  (415) 616-1199
                                     Attention:  Michael J. Kennedy


                                     S MERGER CORP.


                                     By:   \s\ KATHLEEN SEREDA GLAUB
                                          ______________________________________
                                          Kathleen Sereda Glaub
                                          Chairman of the Board and President

                                     c/o Cell Genesys, Inc.
                                     322 Lakeside Drive
                                     Foster City, California  94404
                                     Telephone:  (415) 358-9600
                                     Telecopy:  (415) 358-0230
                                     Attention:  Kathleen Sereda Glaub
<PAGE>   86
                                       SOMATIX THERAPY CORPORATION


                                       By:   \s\ EDWARD O. LANPHIER
                                            ____________________________________
                                            Edward O. Lanphier II
                                            Executive Vice President and
                                                 Chief Financial Officer

                                       950 Marina Village Parkway
                                       Suite 100
                                       Alameda, California  94501
                                       Telephone:  (510) 748-3000
                                       Telecopy:  (510) 814-8002
                                       Attention:  Edward O. Lanphier

                                       with a copy to:

                                       Brobeck, Phleger & Harrison
                                       2200 Geng Road
                                       Palo Alto, California  94303
                                       Telephone:  (415) 424-0160
                                       Telecopy:  (415) 496-2885
                                       Attention:  J. Stephan Dolezalek
<PAGE>   87
                                                                      EXHIBIT 2

                                                                  CONFORMED COPY


                             STOCK OPTION AGREEMENT

                  STOCK OPTION AGREEMENT, dated as of January 12, 1997 (as
amended, restated, supplemented or otherwise modified from time to time, this
"Agreement"), between CELL GENESYS, INC., a corporation organized and existing
under the laws of the State of Delaware ("CGI"), as the grantor hereunder (the
"Grantor"), and SOMATIX THERAPY CORPORATION, a corporation organized and
existing under the laws of the State of Delaware ("STC"), as the grantee
hereunder (the "Grantee");


                              W I T N E S S E T H:

                  WHEREAS, CGI, S Merger Corp., a corporation organized and
existing under the laws of the State of Delaware and a direct wholly owned
subsidiary of CGI, and STC have entered into an agreement and plan of merger and
reorganization, dated as of January 12, 1997 (the "Merger Agreement"; terms used
and not otherwise defined herein are used herein as defined in the Merger
Agreement); and

                  WHEREAS, as a condition to the willingness of STC to enter
into the Merger Agreement and the STC Stock Option Agreement, STC has required
that CGI agree, and in order to induce STC to enter into the Merger Agreement
and the STC Stock Option Agreement, CGI has agreed to grant STC an option, upon
the terms and subject to the conditions set forth in this Agreement, to purchase
up to 3,286,703 newly issued shares of common stock, par value $.001 per share,
of CGI (the "Grantor Common Stock"), representing approximately 19.9% of the
shares of Grantor Common Stock issued and outstanding on the date hereof;

                  NOW, THEREFORE, in consideration of the foregoing and the
representations, warranties, covenants and agreements set forth herein and in
the Merger Agreement, and other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, and intending to be legally bound
hereby, the parties hereto hereby agree as follows:


                  SECTION 1. Grant of Stock Option. The Grantor hereby grants to
the Grantee an irrevocable option (the "Stock Option") to purchase up to
3,286,703 shares of Grantor Common Stock (the "Option Shares") at a purchase
price of $9.12 per Option Share (the "Purchase Price").

                  SECTION 2.  Exercise of Stock Option.  (a)  Subject to the 
conditions set forth in Section 3, the Stock Option may be exercised by the
Grantee, in whole or in part, at any
<PAGE>   88
                                        2

time or from time to time after the occurrence of an Exercise Event (as defined
below) and prior to the Termination Date (as defined below).

                  (b) An "Exercise Event" shall occur for purposes of this
Agreement upon the occurrence of any event or circumstance which obligates the
Grantor, or, in the case of Section 9.05(c)(ii) of the Merger Agreement, may
obligate the Grantor in the event a Competing Transaction is consummated within
the 12-month period referred to therein, to pay to the Grantee any amount
specified pursuant to Section 9.05 of the Merger Agreement.

                  (c) The "Termination Date" shall occur for purposes of this
Agreement upon the first to occur of any of (i) the Effective Time; (ii) the
termination of this Agreement pursuant to Section 10; or (iii) the date which is
90 days after the occurrence of an Exercise Event.

                  (d) In the event the Grantee wishes to exercise the Stock
Option, the Grantee shall send a written notice (a "Stock Exercise Notice") to
the Grantor specifying the total number of Option Shares the Grantee wishes to
purchase, the denominations of the certificate or certificates evidencing such
Option Shares which the Grantee wishes to receive, a date (a "Closing Date"),
which shall be a business day which is at least five and not more than 10
business days after delivery of such notice, and place for the closing of such
purchase (a "Closing"). Upon receipt of a Stock Exercise Notice, the Grantor
shall be obligated to deliver to the Grantee a certificate or certificates
evidencing the number of Option Shares specified therein, in accordance with the
terms of this Agreement, on the later of (i) the date specified in such Stock
Exercise Notice and (ii) the first business day on which the conditions
specified in Section 3 shall be satisfied; provided, however, that
notwithstanding the foregoing, the Grantor shall have the right, exercisable by
written notice to the Grantee within three business days after receipt of a
Stock Exercise Notice, to elect to treat such Stock Exercise Notice as a Cash
Exercise Notice pursuant to Section 2(e) for all purposes of this Agreement, and
to pay to the Grantee an amount in cash equal to the Spread (as defined below)
within 10 business days following receipt of such Stock Exercise Notice.

                  (e) If at any time the Stock Option is then exercisable
pursuant to the terms of Section 2(a), the Grantee may elect, in lieu of
exercising the Stock Option to purchase Option Shares as provided in Section
2(a), to send a written notice to the Grantor (a "Cash Exercise Notice"; either
a Cash Exercise Notice or a Stock Exercise Notice, an "Exercise Notice")
specifying a date which shall be a business day which is at least five and not
more than 10 business days following the date such notice is given on which date
the Grantor shall pay to the Grantee an amount in cash equal to the Spread (as
defined below) multiplied by such number of Option Shares as the Grantee shall
specify. As used herein, "Spread" shall mean the excess, if any, over the
Purchase Price of the higher of (i) if applicable, the highest price per share
of the Grantor Common Stock paid by any person in a Competing Transaction (the
"Competing Purchase Price") or (ii) the closing price of the shares of
<PAGE>   89
                                        3

Grantor Common Stock on the NMS on the last trading day immediately prior to the
date of the Cash Exercise Notice (the "Closing Price"). If the Competing
Purchase Price includes any property other than cash, the Competing Purchase
Price shall be the sum of (i) the fixed cash amount, if any, included in the
Competing Purchase Price plus (ii) the fair market value of such other property.
If such other property consists of securities with an existing public trading
market, the average of the closing prices (or the average of the closing bid and
asked prices if closing prices are unavailable) for such securities in their
principal public trading market on the five trading days ending one trading day
prior to the date of the Cash Exercise Notice shall be deemed to equal the fair
market value of such property. If such other property consists of something
other than cash or securities with an existing public trading market and, as of
the payment date for the Spread, agreement on the value of such other property
has not been reached, the Competing Purchase Price shall be deemed to be the
amount of any cash included in the Competing Purchase Price plus the fair market
value of such other property (as determined by a nationally recognized
investment banking firm jointly selected by the Grantor and the Grantee). For
this purpose, the parties shall use commercially reasonable efforts to cause any
determination of the fair market value of such other property to be made within
three business days after the date of delivery of the Cash Exercise Notice. Upon
exercise of its right to receive the Spread pursuant to this Section 2(e) or the
Grantor electing to treat a Stock Exercise Notice as a Cash Exercise Notice
pursuant to Section 2(d), the obligations of the Grantor to deliver Option
Shares pursuant to Section 3 shall be terminated with respect to such number of
Option Shares for which the Grantee shall have elected to be paid the Spread. If
at the time payment of the Spread by the Grantor is due, the Grantor shall not
have consummated a Competing Transaction, the Grantor may elect to pay the
Spread in cash or in shares of Grantor Common Stock, valued at the closing price
of shares of Grantor Common Stock on the NMS on the business day prior to such
payment (the "Closing Date Price").

                  SECTION 3. Conditions to Delivery of Option Shares. The
obligation of the Grantor to deliver Option Shares upon any exercise of the
Stock Option is subject to the following conditions:

                           (a) Such delivery or payment shall not in any
         material respect violate, or otherwise cause the material violation of,
         the rules and regulations of the NASD or any material Law, including,
         without limitation, the HSR Act, applicable to such exercise of the
         Stock Option and the delivery of the Option Shares or payment of the
         Spread in respect of such exercise; and

                           (b) There shall be no preliminary or permanent
         injunction or other order by any court of competent jurisdiction
         preventing or prohibiting such exercise of the Stock Option or the
         delivery of the Option Shares or payment of the Spread in respect of
         such exercise.
<PAGE>   90
                                        4

                  SECTION 4. Closings. (a) At each Closing pursuant to Section
2(d), the Grantor shall deliver to the Grantee a certificate or certificates
evidencing the number of Option Shares specified in the applicable Stock
Exercise Notice (in the denominations specified therein), and the Grantee shall
purchase each such Option Share from the Grantor at the Purchase Price.

                  (b) At each Closing pursuant to Section 2(e), the Grantor
shall deliver to the Grantee cash in an amount determined pursuant to Section
2(e).

                  (c)(i)  Certificates evidencing Option Shares delivered 
hereunder may, at the election of the Grantor, contain the following legend:

                  THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN
         REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE
         SECURITIES LAWS, AND MAY NOT BE TRANSFERRED, SOLD, ASSIGNED, PLEDGED,
         HYPOTHECATED OR OTHERWISE DISPOSED OF, AND NO REGISTRATION OF TRANSFER
         OF SUCH SECURITIES WILL BE MADE ON THE BOOKS OF THE ISSUER, UNLESS SUCH
         TRANSFER, SALE, ASSIGNMENT, PLEDGE, HYPOTHECATION OR OTHER DISPOSAL IS
         MADE IN CONNECTION WITH AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
         SECURITIES ACT OF 1933, AS AMENDED, AND ANY APPLICABLE STATE SECURITIES
         LAWS OR IS EXEMPT FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT, THE
         RULES AND REGULATIONS IN EFFECT THEREUNDER AND ANY APPLICABLE STATE
         SECURITIES LAWS.

         (ii) The Grantor shall, upon the written request of the holder thereof,
issue such holder a new certificate evidencing such Option Shares without such
legend in the event (A) such Option Shares have been registered pursuant to the
Securities Act, (B) such Option Shares have been sold in reliance on and in
accordance with Rule 144 promulgated under the Securities Act or (C) such holder
shall have delivered to the Grantor an opinion of counsel, in form and substance
reasonably satisfactory to the Grantor, to the effect that subsequent transfers
of such Option Shares may be effected without registration under the Securities
Act.

                  (d) All payments made pursuant to this Section 4 shall be made
by wire transfer of immediately available funds.

                  SECTION 5. Adjustments upon Share Issuances, Changes in
Capitalization, Etc. (a) In the event of any change in the Grantor Common Stock
or in the number of outstanding shares of Grantor Common Stock by reason of a
stock dividend, split-up, recapitalization, combination, exchange of shares or
similar transaction or any other change
<PAGE>   91
                                        5

in the corporate or capital structure of the Grantor (including, without
limitation, the declaration or payment of an extraordinary dividend of cash,
securities or other property), the type and number of shares or securities to be
issued by the Grantor upon exercise of the Stock Option shall be adjusted
appropriately, and proper provision shall be made in the agreements governing
such transaction, so that the Grantee shall receive upon exercise of the Stock
Option the number and class of shares or other securities or property that the
Grantee would have received in respect of the Grantor Common Stock if the Stock
Option had been exercised immediately prior to such event, or the record date
therefor, as applicable, and elected to the fullest extent it would have been
permitted to elect to receive such securities, cash or other property.

                  (b) In the event that the Grantor shall enter into an
agreement (i) to consolidate with or merge into any person, other than the
Grantee or any of its subsidiaries, and shall not be the continuing or surviving
corporation of such consolidation or merger, (ii) to permit any person, other
than the Grantee or any of its subsidiaries, to merge into the Grantor and the
Grantor shall be the continuing or surviving corporation, but, in connection
with such merger, the then outstanding shares of Grantor Common Stock shall be
changed into or exchanged for stock or other securities of the Grantor or any
other person or cash or any other property or then outstanding shares of Grantor
Common Stock would after such merger represent less than a majority of the
outstanding shares and share equivalents of the surviving corporation or (iii)
to sell or otherwise transfer all or substantially all of its assets to any
person, other than the Grantee or any of its subsidiaries, then, and in each
such case, proper provision shall be made in the agreements governing such
transaction so that the Grantee shall receive upon exercise of the Stock Option
the number and class of shares or other securities or property that the Grantee
would have received in respect of the Grantor Common Stock if the Stock Option
had been exercised immediately prior to such transaction, or the record date
therefor, as applicable, and elected to the fullest extent it would have been
permitted to elect to receive such securities, cash or other property.

                  (c) All of the provisions of this Agreement shall apply with
appropriate adjustments to any securities for which the Stock Option becomes
exercisable pursuant to this Section 5.

                  SECTION 6. Representations and Warranties of the Grantor. The
Grantor hereby represents and warrants to the Grantee as follows:

                           (a) Organization; Authority Relative to This
         Agreement. The Grantor has been duly organized and is validly existing
         and in good standing under the laws of the State of Delaware. The
         Grantor has all necessary corporate power and authority to execute and
         deliver this Agreement, to perform its obligations hereunder and to
         consummate the transactions contemplated hereby. The execution and
         delivery of this Agreement by the Grantor and the consummation by the
         Grantor
<PAGE>   92
                                        6

         of the transactions contemplated hereby have been duly and validly
         authorized by the board of directors of the Grantor, and no other
         corporate proceedings on the part of the Grantor are necessary to
         authorize this Agreement or to consummate such transactions. This
         Agreement has been duly and validly executed and delivered by the
         Grantor and, assuming the due authorization, execution and delivery by
         the Grantee, constitutes a legal, valid and binding obligation of the
         Grantor, enforceable against the Grantor in accordance with its terms.
         The Grantor has taken all appropriate actions so that the restrictions
         on business combinations contained in Section 203 of the General
         Corporation Law will not apply with respect to or as a result of the
         transactions contemplated hereby.

                           (b) Authority to Issue Shares. The Grantor has taken
         all necessary corporate action to authorize and reserve and permit it
         to issue, and at all times from the date hereof through the Termination
         Date shall have reserved, all the Option Shares issuable pursuant to
         this Agreement, and the Grantor will take all necessary corporate
         action to authorize and reserve and permit it to issue all additional
         shares of Grantor Common Stock or other securities which may be issued
         pursuant to Section 4, all of which, upon their issuance and delivery
         in accordance with the terms of this Agreement, will be duly
         authorized, validly issued, fully paid and nonassessable, will be
         delivered free and clear of all security interests, liens, claims,
         pledges, options, rights of first refusal, agreements, limitations on
         the Grantee's voting rights, charges and other encumbrances of any
         nature whatsoever (other than this Agreement) and will not be subject
         to any preemptive rights.

                           (c) No Conflict; Required Filings and Consents. The
         execution and delivery of this Agreement by the Grantor do not, and the
         performance of this Agreement by the Grantor will not, (i) require any
         consent, approval, authorization or permit of, or filing with or
         notification to any Governmental Entity, other than pursuant to the HSR
         Act, (ii) conflict with or violate any provision of the certificate of
         incorporation or by-laws or equivalent organizational documents of the
         Grantor or any material subsidiary thereof, (iii) conflict with or
         violate any Law applicable to the Grantor or any material subsidiary
         thereof or by which any property or asset of the Grantor or any
         material subsidiary thereof is bound or affected, or (iv) result in any
         breach of or constitute a default (or an event which with notice or
         lapse of time or both would become a default) under, or give to others
         any right of termination, amendment, acceleration or cancellation of,
         or result in the creation of a lien or other encumbrance of any nature
         whatsoever on any property or asset of the Grantor or any material
         subsidiary thereof pursuant to, any note, bond, mortgage, indenture,
         contract, agreement, lease, license, permit, franchise or other
         instrument or obligation to which the Grantor or any material
         subsidiary thereof is a party or by which the Grantor or any material
         subsidiary thereof or any property or asset of the Grantor or any
         material subsidiary thereof is bound or affected, except, in the case
         of clauses (i),
<PAGE>   93
                                        7

         (iii) and (iv), for any such conflicts, violations, breaches, defaults
         or other occurrences which could not reasonably be expected to prevent
         or delay in any material respect the exercise by the Grantee of the
         Stock Option or any other right of the Grantee under this Agreement.

                  SECTION 7. Covenants of the Grantor. (a) Listing; Other
Action. (i) The Grantor shall, at its expense, use its best efforts to cause the
Option Shares to be listed for quotation on the NMS, subject to notice of
issuance, as promptly as practicable following the date of this Agreement, and
will provide prompt notice to the NASD of the issuance of each Option Share.

         (ii) The Grantor shall use its best efforts to take, or cause to be
taken, all appropriate action, and to do, or cause to be done, all things
necessary, proper or advisable under applicable Law to consummate and make
effective the transactions contemplated hereunder, including, without
limitation, using all commercially reasonable efforts to obtain all licenses,
permits, consents, approvals, authorizations, qualifications and orders of
Governmental Entities. Without limiting the generality of the foregoing, the
Grantor shall, when required in order to effect the transactions contemplated
hereunder, make all necessary filings and any other required or appropriate
submissions under the HSR Act as promptly as practicable.

         (iii) The Grantor shall not take any action in order to intentionally
cause the exercise of the Stock Option to violate, or to require the vote of the
stockholders of the Grantor in order not to violate, any rules or regulations of
the NASD.

               (b) Registration. Upon the request of the Grantee at any time
and from time to time within three years of the first Closing, the Grantor shall
(i) effect, as promptly as practicable, up to two registrations under the
Securities Act covering any part or all (as may be requested by the Grantee) of
the Option Shares or other securities that have been acquired by or are issuable
to the Grantee upon exercise of the Stock Option, and to use its best efforts to
qualify such Option Shares or other securities under any applicable state
securities laws and (ii) include any part or all of the Option Shares or such
other securities in any registration statement for common stock filed by the
Grantor under the Securities Act in which such inclusion is permitted under
applicable rules and regulations, and to use its best efforts to keep each such
registration described in clauses (i) and (ii) effective for a period of not
less than six months. If the managing underwriter of a proposed offering of
securities by the Grantor shall advise the Grantor in writing that, in the
reasonable opinion of the managing underwriter, the distribution of the Option
Shares requested by the Grantee to be included in a registration statement
concurrently with securities being registered for sale by the Grantor would
adversely affect the distribution of such securities by the Grantor, then the
Grantor shall either (i) include such Option Shares in the registration
statement, but the Grantee shall agree to delay the offering and sale for such
period of time as the managing
<PAGE>   94
                                        8

underwriter may reasonably request (provided that the Grantee may at any time
withdraw its request to include Option Shares in such offering) or (ii) include
such portion of the Option Shares in the registration statement as the managing
underwriter advises may be so included for sale simultaneously with sales by the
Grantor. The registrations effected under this Section 7(b) shall be effected at
the Grantor's expense except for underwriting commissions allocable to the
Option Shares and the fees and disbursements of the Grantee's counsel. The
Grantor shall indemnify and hold harmless the Grantee, its affiliates and
controlling persons and their respective officers, directors, agents and
representatives from and against any and all losses, claims, damages,
liabilities and expenses (including, without limitation, all out-of-pocket
expenses, investigation expenses, expenses incurred with respect to any judgment
and fees and disbursements of counsel and accountants) arising out of or based
upon any statements contained in, or omissions or alleged omissions from, each
registration statement (and related prospectus) filed pursuant to this Section
7(b); provided, however, that the Grantor shall not be liable in any such case
to the Grantee or any affiliate or controlling person of the Grantee or any of
their respective officers, directors, agents or representatives to the extent
that any such loss, claim, damage, liability (or action or proceeding in respect
thereof) or expense arises out of or is based upon an untrue statement or
omission made in such registration statement or prospectus in reliance upon, and
in conformity with, written information with respect to the Grantee or any such
affiliate, controlling person, officer, director, agent or representative
thereof, as the case may be, furnished by the Grantee or any such other person
to the Grantor for use in the preparation of such registration statement.

                  SECTION 8. Representations and Warranties of the Grantee. The
Grantee hereby represents and warrants to the Grantor as follows:

                           (a)  Organization; Authority Relative to This 
         Agreement. The Grantee has been duly organized and is validly existing
         and in good standing under the laws of the State of Delaware. The
         Grantee has all necessary corporate power and authority to execute and
         deliver this Agreement, to perform its obligations hereunder and to
         consummate the transactions contemplated hereby. The execution and
         delivery of this Agreement by the Grantee and the consummation by the
         Grantee of the transactions contemplated hereby have been duly and
         validly authorized by the board of directors of the Grantee, and no
         other corporate proceedings on the part of the Grantee are necessary to
         authorize this Agreement or to consummate such transactions. This
         Agreement has been duly and validly executed and delivered by the
         Grantee and, assuming the due authorization, execution and delivery by
         the Grantor, constitutes a legal, valid and binding obligation of the
         Grantee, enforceable against the Grantee in accordance with its terms.

                           (b) No Conflict; Required Filings and Consents.  The
         execution and delivery of this Agreement by the Grantee do not, the
         performance of this Agreement by the Grantee will not, (i) require any
         consent, approval, authorization or permit of,
<PAGE>   95
                                        9

         or filing with or notification to any Governmental Entity, other than
         pursuant to the HSR Act, (ii) conflict with or violate any provision of
         the certificate of incorporation or by-laws or equivalent
         organizational documents of the Grantee, (iii) conflict with or violate
         any Law applicable to the Grantee or by which any property or asset of
         the Grantee is bound or affected, or (iv) result in any breach of or
         constitute a default (or an event which with notice or lapse of time or
         both would become a default) under, or give to others any right of
         termination, amendment, acceleration or cancellation of, or result in
         the creation of a lien or other encumbrance of any nature whatsoever on
         any property or asset of the Grantee pursuant to, any note, bond,
         mortgage, indenture, contract, agreement, lease, license, permit,
         franchise or other instrument or obligation to which the Grantee is a
         party or by which the Grantee or any property or asset of the Grantee
         is bound or affected, except, in the case of clauses (i), (iii) and
         (iv), for any such conflicts, violations, breaches, defaults or other
         occurrences which could not reasonably be expected, individually or in
         the aggregate, (A) to prevent or delay in any material respect the
         exercise by the Grantor of any right of the Grantor under this
         Agreement or (B) to have a CGI Material Adverse Effect.

                  SECTION 9. Covenants of the Grantee. The Grantee shall acquire
the Option Shares for investment purposes only and not with a view to any
distribution thereof in violation of the Securities Act, and shall not sell any
Option Shares purchased pursuant to this Agreement except in compliance with the
Securities Act.

                  SECTION 10. Termination. This Agreement, other than the rights
and obligations of the Grantor and the Grantee under Sections 7, 9 and 11 shall
terminate on February 12, 1998.

                  SECTION 11. Miscellaneous. (a) Expenses. Except as otherwise
provided herein or in the Merger Agreement, all costs and expenses incurred in
connection with the transactions contemplated by this Agreement shall be paid by
the party incurring such expenses.

                  (b) Notices. All notices and other communications given or
made pursuant hereto shall be in writing and shall be deemed to have been duly
given or made as of the date delivered, mailed or transmitted, and shall be
effective upon receipt, if delivered personally, mailed by registered or
certified mail (postage prepaid, return receipt requested) to the respective
parties at their addresses as specified in the Merger Agreement or sent by
electronic transmission to the respective parties at their telecopier numbers as
specified in Section 10.02 of the Merger Agreement.

                  (c) Assignment. This Agreement may not be assigned by
operation of law or otherwise without the express written consent of each party
hereto (which consent may be granted or withheld in the sole discretion of each
such party); provided, however, that the
<PAGE>   96
                                       10

Grantee may assign all or any of its rights and obligations hereunder to any
wholly owned subsidiary of the Grantee; provided further that no such assignment
shall relieve the Grantee of its obligations hereunder if such assignee does not
perform such obligations.

                  (d) Amendment; Waiver. This Agreement may not be amended
except by an instrument in writing signed by the parties hereto. Any party
hereto may (i) extend the time for the performance of any obligation or other
act of any other party hereto, (ii) waive any inaccuracy in the representations
and warranties contained herein or in any document delivered pursuant hereto and
(iii) waive compliance with any agreement or condition contained herein. Any
such extension or waiver shall be valid if set forth in an instrument in writing
signed by the party or parties to be bound thereby. No failure or delay by any
party in exercising any right, power or privilege hereunder shall operate as a
waiver thereof nor shall any single or partial exercise thereof preclude any
other or further exercise thereof or the exercise of any other right, power or
privilege. The rights and remedies herein provided shall be cumulative and not
exclusive of any rights or remedies provided by law.

                  (e) Successors and Assigns. The provisions of this Agreement
shall be binding upon and inure to the benefit of the parties hereto and their
respective successors and permitted assigns.

                  (f) No Third Party Beneficiaries. Nothing herein, express or
implied, is intended to or shall confer upon any person, other than the parties
hereto and their respective successors and assigns, any legal or equitable
right, benefit or remedy of any nature whatsoever, under or by reason of this
Agreement.

                  (g) Governing Law.  THIS AGREEMENT SHALL BE GOVERNED BY, AND
CONSTRUED AND ENFORCED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF DELAWARE,
WITHOUT REGARD TO THE PRINCIPLES THEREOF REGARDING CONFLICT OF LAWS.

                  (h) Waiver of Jury Trial. EACH PARTY HERETO HEREBY IRREVOCABLY
WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY PROCEEDING (WHETHER BASED ON CONTRACT,
TORT OR OTHERWISE) ARISING OUT OF OR RELATING TO THIS AGREEMENT OR ANY
TRANSACTION OR AGREEMENT CONTEMPLATED HEREBY OR THE ACTIONS OF ANY PARTY HERETO
IN THE NEGOTIATION, ADMINISTRATION, PERFORMANCE OR ENFORCEMENT HEREOF.

                  (i) Specific Performance. The parties hereto agree that
irreparable damage would occur in the event any provision of this Agreement was
not performed in accordance with the terms hereof and that the parties shall be
entitled to specific performance of the terms hereof, in addition to any other
remedy at law or in equity.
<PAGE>   97
                                       11

                  (j) Severability. If it shall be determined by court order not
subject to appeal or discretionary review that any provision or wording of this
Agreement shall be invalid or unenforceable under applicable law, such
invalidity or unenforceability shall not invalidate the entire Agreement and
shall be construed so as to limit any term or provision so as to make it
enforceable or valid within the requirements of applicable law, and, in the
event such term or provision cannot be so limited, this Agreement shall be
construed to omit such invalid or unenforceable provisions.

                  (k) Entire Agreement. This Agreement and the Merger Agreement,
including any exhibits or schedules hereto or thereto, or any other instruments,
agreements or documents referenced herein or therein, constitute the entire
agreement among the parties hereto with respect to the subject matter hereof,
and supersede all other prior agreements or undertakings with respect thereto,
both written and oral.

                  (l) Headings.  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.

                  (m) Counterparts. This Agreement may be executed in one or
more counterparts, and by the different parties hereto in separate counterparts,
each of which when executed shall be deemed to be an original but all of which
taken together shall constitute one and the same agreement.

                  (n) Further Assurances. Each party hereto shall execute,
acknowledge, deliver, file, record and publish such further certificates,
instruments, documents and amendments, and do all such further acts and things
as may be required by law or to carry out the intent and purposes of this
Agreement.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
<PAGE>   98
                  IN WITNESS WHEREOF, the parties hereto have caused this
Agreement to be executed as of the date first written above by their respective
officers thereunto duly authorized.


                                     CELL GENESYS, INC.


                                     By:   \s\ STEPHEN A. SHERWIN
                                          ______________________________________
                                          Stephen A. Sherwin, M.D.
                                          Chairman of the Board, President and
                                               Chief Executive Officer


                                     SOMATIX THERAPY CORPORATION


                                     By:   \s\ EDWARD O. LANPHIER
                                          ______________________________________
                                          Edward O. Lanphier II
                                          Executive Vice President and
                                               Chief Financial Officer



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