LIGAND PHARMACEUTICALS INC
8-A12G, 1996-09-30
PHARMACEUTICAL PREPARATIONS
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<PAGE>   1




                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549



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


                                    FORM 8-A



               FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                    PURSUANT TO SECTION 12(b) OR (g) OF THE
                        SECURITIES EXCHANGE ACT OF 1934




                      LIGAND PHARMACEUTICALS INCORPORATED
             (Exact name of Registrant as specified in its charter)



<TABLE>
         <S>                                                                 <C>
                          Delaware                                                     77-0160744
         (State of incorporation or organization)                            (IRS Employer Identification No.)
</TABLE>


                            9393 Towne Centre Drive
                          San Diego, California 92121
              (Address of principal executive offices) (Zip Code)



       Securities to be registered pursuant to Section 12(b) of the Act:

<TABLE>
<S>                                                   <C>
 TITLE OF EACH CLASS TO BE SO REGISTERED              NAME OF EACH EXCHANGE ON WHICH EACH CLASS IS 
                                                                 TO BE REGISTERED
                None                                                    None
</TABLE>

       Securities to be registered pursuant to Section 12(g) of the Act:

                        Preferred Share Purchase Rights
                                (Title of Class)
<PAGE>   2
ITEM 1.  DESCRIPTION OF SECURITIES TO BE REGISTERED.

         Effective as of September 13, 1996, pursuant to a Preferred Shares
Rights Agreement (the "Rights Agreement") between Ligand Pharmaceuticals
Incorporated (the "Company") and Wells Fargo Bank N.A., as Rights Agent (the
"Rights Agent"), the Company's Board of Directors declared a dividend of one
right (a "Right") to purchase one one-thousandth share of the Company's Series
A Participating Preferred Stock ("Series A Preferred") for each outstanding
share of Common Stock, par value $0.001 per share ("Common Shares"), of the
Company.  The dividend is payable on September 30, 1996 (the "Record Date") to
stockholders of record as of the close of business on that date.  Each Right
entitles the registered holder to purchase from the Company one one-thousandth
of a share of Series A Preferred at an exercise price of $100 (the "Purchase
Price"), subject to adjustment in the event the Company declares a dividend on
the Common Stock payable in Common Stock, subdivides the number of outstanding
shares of Common Stock into a larger number of such shares or combines the
number of outstanding shares of Common Stock into a smaller number of such
shares, among other circumstances.  In addition, under certain circumstances
described more fully herein, the Rights may become exercisable for a number of
Common Shares having a value equal to two times the Purchase Price and/or
Common Stock of certain acquiring companies having a value equal to two times
the Purchase Price.

         The following summary of the principal terms of the Rights Agreement
is a general description only and is subject to the detailed terms and
conditions of the Rights Agreement.  A copy of the Rights Agreement is attached
as Exhibit 99.1 to this Registration Statement and is incorporated herein by
reference; capitalized terms used but not otherwise defined herein shall have
the meanings ascribed to them in the Rights Agreement.

CERTAIN ANTI-TAKEOVER EFFECTS

         The Rights approved by the Board are designed to protect and maximize
the value of the outstanding equity interests in the Company in the event of an
unsolicited attempt by an acquiror to take over the Company, in a manner or on
terms not approved by the Board of Directors.  Takeover attempts frequently
include coercive tactics to deprive the Company's Board of Directors and its
stockholders of any real opportunity to determine the destiny of the Company.

         The Rights have been declared by the Board in order to deter such
tactics, including a gradual accumulation in the open market of a 20% or
greater position to be followed by a merger or a partial or two-tier tender
offer that does not treat all stockholders equally.  These tactics can operate
to unfairly pressure stockholders, force them out of their investment and
deprive them of the full value of their shares.

         The Rights are not intended to prevent a takeover of the Company and
will not do so.  The Rights may be redeemed by the Company at $.01 per Right
within ten days (or on such later date as may be determined by a majority of
the Board of Directors, excluding directors affiliated with an Acquiring
Person) after the accumulation of 20% or more of the Company's shares by a
single acquiror or group.  Accordingly, the Rights should not





                                      -2-
<PAGE>   3
interfere with any merger or business combination approved by the Board of
Directors.

         However, the Rights may have the effect of rendering more difficult or
discouraging an acquisition of the Company deemed undesirable by the Board of
Directors.  The Rights may cause substantial dilution to a person or group that
attempts to acquire the Company on terms or in a manner not approved by the
Company's Board of Directors, except pursuant to an offer conditioned upon the
negation, purchase or redemption of the Rights.  As a result, while the Rights
may provide the Board with leverage to obtain a higher price from a potential
acquiror, they may also prevent or deter offers not approved by the Board, and
therefore deprive stockholders, without providing them with the opportunity to
vote thereon, of the benefits of offers which may be at a higher price than the
current market price of the Company's Common Stock.  In addition, assuming an
active trading market in the Rights themselves does not develop, stockholders
with lesser financial means might not be able to take full economic advantage
of the Rights.  Further, the implementation of a rights plan may heighten the
susceptibility of the Company to greenmail by stockholders who threaten to
acquire a sufficient equity position to pass the Rights' triggering threshold,
although the Board can respond to any such action by redeeming the Rights at
$.01 per Right.

         Issuance of the Rights does not in any way weaken the financial
strength of the Company or interfere with its business plans.  The issuance of
the Rights themselves has no dilutive effect, will not affect reported earnings
per share, should not be taxable to the Company or to its stockholders, and
will not change the way in which the Company's shares are presently traded.
The Company's Board of Directors believes that the Rights represent a sound and
reasonable means of addressing the complex issues of corporate policy created
by the current takeover environment.

RIGHTS EVIDENCED BY COMMON SHARE CERTIFICATES

         The Rights will not be exercisable until the Distribution Date
(defined below).  Prior to the Distribution Date, certificates for the Rights
("Rights Certificates") will not be sent to stockholders and the Rights will
attach to and trade only together with the Common Shares.  Accordingly, Common
Share certificates outstanding on the Record Date will evidence the Rights
related thereto, and Common Share certificates issued after the Record Date but
prior to the Distribution Date will contain a notation incorporating the Rights
Agreement by reference.  Until the Distribution Date (or earlier redemption or
expiration of the Rights), the surrender or transfer of any certificates for
Common Shares, even without notation or a copy of the Summary of Rights being
attached thereto (but as to certificates representing Common Shares issued
after the Record Date, only if they bear the legend required by the Rights
Agreement), will also constitute the transfer of the Rights associated with the
Common Shares represented by such certificate.





                                      -3-
<PAGE>   4
DISTRIBUTION DATE

         The Rights will separate from the Common Shares, Rights Certificates
will be issued and the Rights will become exercisable upon the earlier of: (i)
10 days (or such later date as may be determined by a majority of the Board of
Directors, excluding directors affiliated with the Acquiring Person, as defined
below (the "Continuing Directors")) following a public announcement that a
person or group of affiliated or associated persons (an "Acquiring Person") has
acquired, or obtained the right to acquire, beneficial ownership of 20% or more
of the outstanding Common Shares, or (ii) 10 days (or such later date as may be
determined by a majority of the Continuing Directors) following the
commencement of, or announcement of an intention to make, a tender offer or
exchange offer the consummation of which would result in the beneficial
ownership by a person or group of 20% or more of the outstanding Common Shares.
The earlier of such dates is referred to as the "Distribution Date."

ISSUANCE OF RIGHTS CERTIFICATES; EXPIRATION OF RIGHTS

         As soon as practicable following the Distribution Date, separate
Rights Certificates will be mailed to holders of record of the Common Shares as
of the close of business on the Distribution Date and such separate Rights
Certificates alone will evidence the Rights from and after the Distribution
Date.  All Common Shares issued prior to the Distribution Date will be issued
with Rights.  Common Shares issued after the Distribution Date may be issued
with Rights if such shares are issued (i) upon the conversion of outstanding
convertible debentures or any other convertible securities issued after
adoption of the Rights Agreement or (ii) pursuant to the exercise of stock
options or under employee benefit plans or arrangements unless such issuance
would result in (or create a risk that) such options, plans or arrangements
would not qualify for otherwise available special tax treatment.  Except as
otherwise determined by the Board of Directors, no other Common Shares issued
after the Distribution Date will be issued with Rights.  The Rights will expire
on the earliest of (i) September 13, 2006 (the "Final Expiration Date"), (ii)
redemption or exchange of the Rights as described below, or (iii) consummation
of an acquisition of the Company satisfying certain conditions by a person who
acquired shares pursuant to a Permitted Offer as described below.

INITIAL EXERCISE OF THE RIGHTS

         Following the Distribution Date, and until one of the further events
described below, holders of the Rights will be entitled to receive, upon
exercise and the payment of $100 per Right, one one-thousandth share of the
Series A Preferred, subject to adjustment in the event the Company declares a
dividend on the Common Shares payable in Common Shares, subdivides the number
of outstanding shares of Common Shares into a larger number of such shares or
combines the number of outstanding shares of Common Shares into a smaller
number of such shares, among other circumstances.  In addition, under certain
circumstances described more fully herein, the Rights may become exercisable
for Common Shares having a value equal to two times the Purchase Price and/or
Common Stock of certain acquiring companies having a value equal to two times
the Purchase Price.





                                      -4-
<PAGE>   5
RIGHT TO BUY COMPANY COMMON SHARES

         Unless the Rights are earlier redeemed, in the event that an Acquiring
Person becomes the beneficial owner of 20% or more of the Company's Common
Shares then outstanding (other than pursuant to a Permitted Offer), then proper
provision will be made so that each holder of a Right which has not theretofore
been exercised (other than Rights beneficially owned by the Acquiring Person,
which will thereafter be void) will thereafter have the right to receive, upon
exercise and payment of the Purchase Price, Common Shares having a value equal
to two times the Purchase Price.  For example, if the market price of Common
Shares on the Share Acquisition Date (as defined below) was $50.00, a person
holding one Right could purchase 4 Common Shares upon exercise of such Right
($100/25.00), whereas he could only purchase 2 Common Shares ($100/50.00) in
the absence of such Rights.  Rights are not exercisable following the
occurrence of an event as described above until such time as the Rights are no
longer redeemable by the Company as set forth below.

         In the event that the Company does not have sufficient Common Shares
available for all Rights to be exercised, or the Board decides that it is
necessary and not contrary to the interests of Rights holders to do so, the
Company may instead substitute cash, assets or other securities for the Common
Shares for which the Rights would have been exercisable under this provision.

RIGHT TO BUY ACQUIRING COMPANY STOCK

         Similarly, unless the Rights are earlier redeemed, in the event that,
after the Share Acquisition Date, (i) the Company is acquired in a merger or
other business combination transaction, or (ii) 50% or more of the Company's
consolidated assets or earning power are sold (other than in transactions in
the ordinary course of business) (either of which event is referred to herein
as an "Acquisition"), proper provision must be made so that each holder of a
Right which has not theretofore been exercised (other than Rights beneficially
owned by the Acquiring Person, which will thereafter be void) will thereafter
have the right to receive, upon exercise, shares of Common Stock of the
acquiring company having a value equal to two times the Purchase Price (unless
the transaction satisfies certain conditions and is consummated with a person
who acquired shares pursuant to a Permitted Offer, in which case the Rights
will expire).  So (assuming no satisfaction of such conditions) if for example
the market price of the acquiror's stock on the date of the Acquisition were
$25.00, a person holding one Right could purchase 8 shares of the acquiror's
Common Stock upon exercise of such Right ($100/$12.50), whereas he could only
purchase 4 shares of acquiror's Common Stock ($100/$25.00) in the absence of
such Rights.

PERMITTED OFFER

         A Permitted Offer means a tender offer for all outstanding Common
Shares that has been determined by a majority of the Continuing Directors to be
adequate and otherwise in the best interests of the Company and its
stockholders.  Where the Board of Directors has determined that a tender offer
constitutes a Permitted Offer, the Rights will not become





                                      -5-
<PAGE>   6
exercisable to purchase Common Shares or shares of the acquiring company (as
the case may be) at the discounted price described above.

EXCHANGE PROVISION

         At any time after the acquisition by an Acquiring Person of 20% or
more of the Company's outstanding Common Shares and prior to the acquisition by
such Acquiring Person of 50% or more of the Company's outstanding Common
Shares, the Board of Directors of the Company, following the approval of a
majority of the Board of Directors and a majority of the Continuing Directors,
may exchange the Rights (other than Rights owned by the Acquiring Person), in
whole or in part, at an exchange ratio of one Common Share per Right.

REDEMPTION

         At any time on or prior to the close of business on the earlier of (i)
the 10th day following the acquisition by an Acquiring Person (the "Share
Acquisition Date") or such later date as may be determined by a majority of the
Continuing Directors and publicly announced by the Company, or (ii) the Final
Expiration Date of the Rights, the Company may redeem the Rights in whole, but
not in part, at a price of $.01 per Right.

ADJUSTMENTS TO PREVENT DILUTION

         The Purchase Price payable, the number of Rights and the number of
Series A Preferred or Common Shares or other securities or property issuable
upon exercise of the Rights are subject to adjustment from time to time in
connection with the dilutive issuances by the Company as set forth in the
Rights Agreement.  With certain exceptions, no adjustment in the Purchase Price
will be required until cumulative adjustments require an adjustment of at least
1% in such Purchase Price.

CASH PAID INSTEAD OF ISSUING FRACTIONAL SHARES

         No fractional portion less than integral multiples of one
one-thousandth of a Preferred Share will be issued upon exercise of a Right and
in lieu thereof, an adjustment in cash will be made based on the market price
of the Common Shares on the last trading date prior to the date of exercise.

NO STOCKHOLDERS' RIGHTS PRIOR TO EXERCISE

         Until a Right is exercised, the holder thereof, as such, will have no
rights as a stockholder of the Company (other than any rights resulting from
such holder's ownership of Common Shares), including, without limitation, the
right to vote or to receive dividends.

AMENDMENT OF RIGHTS AGREEMENT

    The provisions of the Rights Agreement may be supplemented or amended by the





                                      -6-
<PAGE>   7
Board of Directors in any manner prior to the close of business on the
Distribution Date without the approval of Rights holders.  After the
Distribution Date, the provisions of the Rights Agreement may be amended by the
Board in order to cure any ambiguity, defect or inconsistency, to make changes
which do not adversely affect the interests of holders of Rights (excluding the
interests of any Acquiring Person), or to shorten or lengthen any time period
under the Rights Agreement; provided, however, that no amendment to adjust the
time period governing redemption shall be made at such time as the Rights are
not redeemable or there are not Continuing Directors, the majority of which
agree to such adjustment.

RIGHTS AND PREFERENCES OF THE SERIES A PREFERRED

         Series A Preferred purchasable upon exercise of the Rights will not be
redeemable.  Each share of Series A Preferred will be entitled to an aggregate
dividend of 1,000 times the dividend declared per Common Share.  In the event
of liquidation, the holders of the Series A Preferred will be entitled to a
minimum preferential liquidation payment equal to $1,000 per share.  Each share
of Series A Preferred will have 1,000 votes, voting together with the Common
Shares.  In the event of any merger, consolidation or other transaction in
which the Common Shares are changed or exchanged, each share of Series A
Preferred will be entitled to receive 1,000 times the amount received per
Common Share.  These rights are protected by customary anti-dilution
provisions.

         Because of the nature of the dividend, liquidation and voting rights
of the shares of Series A Preferred, the value of the one one- thousandth
interest in a share of Series A Preferred purchasable upon exercise of each
Right should approximate the value of one Common Share.

ITEM 2.  EXHIBITS.
<TABLE>
<CAPTION>
                          EXHIBIT
                      ----------------
                            <S>               <C>
                            99.1              Preferred Shares Rights Agreement, dated as of 
                                              September 13, 1996 by and between Ligand 
                                              Pharmaceuticals Incorporated and Wells Fargo 
                                              Bank, N.A., including the Certificate of 
                                              Determination, the form of Rights Certificate and 
                                              the Summary of Rights attached thereto as 
                                              Exhibits A, B and C, respectively.

</TABLE>




                                      -7-
<PAGE>   8
                                   SIGNATURE

         Pursuant to the requirements of Section 12 of the Securities Exchange
Act of 1934, the Registrant has duly caused this Registration Statement to be
signed on its behalf by the undersigned, thereto duly authorized.

                                        LIGAND PHARMACEUTICALS
                                        INCORPORATED


Date:  September 30, 1996
                                        By:     /s/ PAUL V. MAIER          
                                           ------------------------------------
                                                    Paul V. Maier
                                         Vice President, Chief Financial Officer
<PAGE>   9
                                 EXHIBIT INDEX



<TABLE>
<CAPTION>                                                                                                     SEQUENTIAL
                           EXHIBIT                                                                               PAGE            
                             NO.          EXHIBIT                                                                 NO.     
                      -----------------   -------                                                            -------------

                             <S>          <C>                                                                    <C>
                             99.1         Preferred Shares Rights Agreement, dated as of September 13,           ____
                                          1996 by and between Ligand Pharmaceuticals Incorporated and
                                          Wells Fargo Bank N.A., including the Certificate of
                                          Determination, the form of Rights Certificate and the Summary
                                          of Rights attached thereto as Exhibits A, B and C,
                                          respectively.
</TABLE>

<PAGE>   1



                                                              EXHIBIT 99.1
                                                              

                      LIGAND PHARMACEUTICALS INCORPORATED

                                      AND

                             WELLS FARGO BANK N.A.
                                  RIGHTS AGENT





                       PREFERRED SHARES RIGHTS AGREEMENT


                         DATED AS OF SEPTEMBER 13, 1996
<PAGE>   2
                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                                                Page
                                                                                                                                ----
<S>              <C>                                                                                                             <C>
Section 1.       Certain Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1

Section 2.       Appointment of Rights Agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5

Section 3.       Issuance of Rights Certificates  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5

Section 4.       Form of Rights Certificates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  7

Section 5.       Countersignature and Registration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  8

Section 6.       Transfer, Split Up, Combination and Exchange of Rights Certificates; Mutilated, Destroyed, Lost or Stolen Rights
                 Certificates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  9

Section 7.       Exercise of Rights; Purchase Price; Expiration Date of Rights. . . . . . . . . . . . . . . . . . . . . . . . . .  9

Section 8.       Cancellation and Destruction of Rights Certificates  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Section 9.       Reservation and Availability of Preferred Shares . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Section 10.      Preferred Shares Record Date.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Section 11.      Adjustment of Purchase Price, Number of Shares or Number of Rights . . . . . . . . . . . . . . . . . . . . . . . 13

Section 12.      Certificate of Adjusted Purchase Price or Number of Shares.  . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Section 13.      Consolidation, Merger or Sale or Transfer of Assets or Earning Power.  . . . . . . . . . . . . . . . . . . . . . 21

Section 14.      Fractional Rights and Fractional Shares  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Section 15.      Rights of Action.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Section 16.      Agreement of Rights Holders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Section 17.      Rights Certificate Holder Not Deemed a Stockholder.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Section 18.      Concerning the Rights Agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Section 19.      Merger or Consolidation or Change of Name of Rights Agent  . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Section 20.      Duties of Rights Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

</TABLE>




                                      (i)
<PAGE>   3
<TABLE>
<S>              <C>                                                                                                          <C>
Section 21.      Change of Rights Agent.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  29

Section 22.      Issuance of New Rights Certificates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30

Section 23.      Redemption.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30

Section 24.      Exchange.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  31

Section 25.      Notice of Certain Events.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  33

Section 26.      Notices  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  33

Section 27.      Supplements and Amendments.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  34

Section 28.      Successors.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  35

Section 29.      Determinations and Actions by the Board of Directors, etc. . . . . . . . . . . . . . . . . . . . . . . . . .  35

Section 30.      Benefits of this Agreement.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  35

Section 31.      Severability.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  35

Section 32.      Governing Law.   . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  36

Section 33.      Counterparts.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  36

Section 34.      Descriptive Headings.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  36


EXHIBITS

Exhibit A        Form of Certificate of Designation

Exhibit B        Form of Rights Certificate

Exhibit C        Summary of Rights


</TABLE>



                                      (ii)
<PAGE>   4
                       PREFERRED SHARES RIGHTS AGREEMENT


         This Preferred Shares Rights Agreement (the "Agreement"), is dated as
of September 13, 1996, between LIGAND PHARMACEUTICALS INCORPORATED, a Delaware
corporation (the "Company"), and WELLS FARGO BANK N.A. (the "Rights Agent").

         On September 13, 1996 (the "Rights Dividend Declaration Date"), the
Board of Directors of the Company authorized and declared a dividend of one
Preferred Share purchase right (a "Right") for each Common Share (as
hereinafter defined) of the Company outstanding as of the Close of Business (as
hereinafter defined) on September 30, 1996 (the "Record Date"), each Right
representing the right to purchase one one-thousandth of a share of Series A
Participating Preferred Stock (as such number may be adjusted pursuant to the
provisions of this Agreement), having the rights, preferences and privileges
set forth in the form of Certificate of Designation of Rights, Preferences and
Privileges of Series A Participating Preferred Stock attached hereto as Exhibit
A, upon the terms and subject to the conditions herein set forth, and further
authorized and directed the issuance of one Right (as such number may be
adjusted pursuant to the provisions of this Agreement) with respect to each
Common Share that shall become outstanding between the Record Date and the
earlier of the Distribution Date and the Expiration Date (as such terms are
hereinafter defined), and in certain circumstances after the Distribution Date.

         NOW, THEREFORE, in consideration of the promises and the mutual
agreements herein set forth, the parties hereby agree as follows:

         SECTION 1.       CERTAIN DEFINITIONS.  For purposes of this Agreement,
the following terms have the meanings indicated:

                 (a)      "Acquiring Person" shall mean any Person who or
which, together with all Affiliates and Associates of such Person, shall be the
Beneficial Owner of 20% or more of the Common Shares then outstanding, but
shall not include the Company, any Subsidiary of the Company, any employee
benefit plan of the Company or of any Subsidiary of the Company, or any entity
holding Common Shares for or pursuant to the terms of any such plan, or
Allergan Ligand Retinoid Therapeutics, Inc. ("ALRT") holding Common Shares
pursuant to the exercise of that certain product purchase option set forth in
the 1057 Purchase Option Agreement dated June 3, 1995 among the Company, ALRT
and Allergan, Inc.  Notwithstanding the foregoing, no Person shall be deemed to
be an Acquiring Person either (i) as the result of an acquisition of Common
Shares by the Company which, by reducing the number of shares outstanding,
increases the proportionate number of shares beneficially owned by such Person
to 20% or more of the Common Shares of the Company then outstanding; provided,
however, that if a Person shall become the Beneficial Owner of 20% or more of
the Common Shares of the Company then outstanding by reason of share purchases
by the Company and shall, after such share purchases by the Company, become the
Beneficial Owner of any additional Common Shares of the Company, then such
Person shall be deemed to be an Acquiring Person.  Notwithstanding the
foregoing, if the Board of Directors of the Company determines in good faith
that a Person who would otherwise
<PAGE>   5
be an "Acquiring Person", as defined pursuant to the foregoing provisions of
this paragraph (a), has become such inadvertently, and such Person divests as
promptly as practicable a sufficient number of Common Shares so that such
Person would no longer be an "Acquiring Person", as defined pursuant to the
foregoing provisions of this paragraph (a), then such Person shall not be
deemed to be an "Acquiring Person" for any purposes of this Agreement.

                 (b)      "Affiliate" and "Associate" shall have the respective
meanings ascribed to such terms in Rule 12b-2 of the General Rules and
Regulations under the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), as in effect on the date of this Agreement.

                 (c)      A Person shall be deemed the "Beneficial Owner" of
and shall be deemed to "beneficially own" any securities:

                          (i)     which such Person or any of such Person's
Affiliates or Associates beneficially owns, directly or indirectly, for
purposes of Section 13(d) of the Exchange Act and Rule 13d-3 thereunder (or any
comparable or successor law or regulation);

                          (ii)    which such Person or any of such Person's
Affiliates or Associates has (A) the right to acquire (whether such right is
exercisable immediately or only after the passage of time) pursuant to any
agreement, arrangement or understanding (other than customary agreements with
and between underwriters and selling group members with respect to a bona fide
public offering of securities), or upon the exercise of conversion rights,
exchange rights, rights (other than the Rights), warrants or options, or
otherwise; provided, however, that a Person shall not be deemed pursuant to
this Section 1(c)(ii)(A) the Beneficial Owner of, or to beneficially own, (1)
securities tendered pursuant to a tender or exchange offer made by or on behalf
of such Person or any of such Person's Affiliates or Associates until such
tendered securities are accepted for purchase or exchange, or (2) securities
which a Person or any of such Person's Affiliates or Associates may be deemed
to have the right to acquire pursuant to any merger or other acquisition
agreement between the Company and such Person (or one or more of its Affiliates
or Associates) if such agreement has been approved by the Board of Directors of
the Company prior to there being an Acquiring Person; or (B) the right to vote
pursuant to any agreement, arrangement or understanding; provided, however,
that a Person shall not be deemed the Beneficial Owner of, or to beneficially
own, any security under this Section 1(c)(ii)(B) if the agreement, arrangement
or understanding to vote such security (1) arises solely from a revocable proxy
or consent given to such Person in response to a public proxy or consent
solicitation made pursuant to, and in accordance with, the applicable rules and
regulations of the Exchange Act and (2) is not also then reportable on Schedule
13D under the Exchange Act (or any comparable or successor report); or

                          (iii)   which are beneficially owned, directly or
indirectly, by any other Person (or any Affiliate or Associate thereof) with
which such Person or any of such Person's Affiliates or Associates has any
agreement, arrangement or understanding, whether or not in writing (other than
customary agreements with and between underwriters and





                                      -2-
<PAGE>   6
selling group members with respect to a bona fide public offering of
securities) for the purpose of acquiring, holding, voting (except to the extent
contemplated by the proviso to Section 1(c)(ii)(B)) or disposing of any
securities of the Company; provided, however, that in no case shall an officer
or director of the Company be deemed (x) the Beneficial Owner of any securities
beneficially owned by another officer or director of the Company solely by
reason of actions undertaken by such persons in their capacity as officers or
directors of the Company or (y) the Beneficial Owner of securities held of
record by the trustee of any employee benefit plan of the Company or any
Subsidiary of the Company for the benefit of any employee of the Company or any
Subsidiary of the Company, other than the officer or director, by reason of any
influence that such officer or director may have over the voting of the
securities held in the plan.

                 (d)      "Business Day" shall mean any day other than a
Saturday, Sunday or a day on which banking institutions in California are
authorized or obligated by law or executive order to close.

                 (e)      "Close of Business" on any given date shall mean 5:00
P.M., California time, on such date; provided, however, that if such date is
not a Business Day it shall mean 5:00 P.M., California time, on the next
succeeding Business Day.

                 (f)      "Common Shares" when used with reference to the
Company shall mean the shares of Common Stock of the Company, par value $0.001
per share.  "Common Shares" when used with reference to any Person other than
the Company shall mean the capital stock (or equity interest) with the greatest
voting power of such other Person or, if such other Person is a Subsidiary of
another Person, the Person or Persons which ultimately control such
first-mentioned Person.

                 (g)      "Continuing Director" shall mean (i) any member of
the Board of Directors of the Company, while a member of the Board, who is not
an Acquiring Person, or an Affiliate or Associate of an Acquiring Person, or a
representative of an Acquiring Person or of any such Affiliate or Associate,
and who was a member of the Board prior to the date of this Agreement, or (ii)
any Person who subsequently becomes a member of the Board, while a member of
the Board, who is not an Acquiring Person, or an Affiliate or Associate of an
Acquiring Person, or a representative of an Acquiring Person or of any such
Affiliate or Associate, if such Person's nomination for election or election to
the Board is recommended or approved by a majority of the Continuing Directors.

                 (h)      "Distribution Date" shall mean the earlier of (i) the
Close of Business on the tenth day (or such later date as may be determined by
action of a majority of Continuing Directors then in office) after the Shares
Acquisition Date (or, if the tenth day after the Shares Acquisition Date occurs
before the Record Date, the Close of Business on the Record Date) or (ii) the
Close of Business on the tenth day (or such later date as may be determined by
action of a majority of Continuing Directors then in office) after the date
that a tender or exchange offer by any Person (other than the Company, any
Subsidiary of the Company, any employee benefit plan of the Company or of any
Subsidiary of the





                                      -3-
<PAGE>   7
Company, or any Person or entity organized, appointed or established by the
Company for or pursuant to the terms of any such plan) is first published or
sent or given within the meaning of Rule 14d-2(a) of the General Rules and
Regulations under the Exchange Act, if, assuming the successful consummation
thereof, such Person would be the Beneficial Owner of 20% or more of the shares
of Common Stock then outstanding.

                 (i)      "Equivalent Shares" shall mean Preferred Shares and
any other class or series of capital stock of the Company which is entitled to
participate in dividends and other distributions, including distributions upon
the liquidation, dissolution or winding up of the Company, on a proportional
basis with the Common Shares.  In calculating the number of any class or series
of Equivalent Shares for purposes of Section 11 of this Rights Agreement, the
number of shares, or fractions of a share, of such class or series of capital
stock that is entitled to the same dividend or distribution as a whole Common
Share shall be deemed to be one share.

                 (j)      "Expiration Date" shall mean the earliest of (i) the
Close of Business on the Final Expiration Date, (ii) the Redemption Date, (iii)
the time at which the Board of Directors orders the exchange of the Rights as
provided in Section 24 hereof or (iv) the consummation of a transaction
contemplated by Section 13(d) hereof.

                 (k)      "Final Expiration Date" shall mean September 13,
2006.

                 (l)      "Permitted Offer" shall mean a tender offer for all
outstanding Common Shares made in the manner prescribed by Section 14(d) of the
Exchange Act and the rules and regulations promulgated thereunder; provided,
however, that such tender offer occurs at a time when Continuing Directors are
in office and a majority of the Continuing Directors then in office has
determined that the offer is both adequate and otherwise in the best interests
of the Company and its stockholders (taking into account all factors that such
Continuing Directors deem relevant).

                 (m)      "Person" shall mean any individual, firm, corporation
or other entity, and shall include any successor (by merger or otherwise) of
such entity.

                 (n)      "Preferred Shares" shall mean shares of Series A
Participating Preferred Stock of the Company.

                 (o)      "Purchase Price" shall have the meaning set forth in
Section 4(a) hereof.

                 (p)      "Record Date" shall have the meaning set forth in the
recitals at the beginning of this Agreement.

                 (q)      "Redemption Date" shall mean the time at which the
Board of Directors of the Company orders redemption of the Rights as provided
in Section 23 hereof.

                 (r)      "Redemption Price" shall have the meaning set forth 
in Section 23(a) hereof.





                                      -4-
<PAGE>   8
                 (s)      "Rights Dividend Declaration Date" shall have the
meaning set forth in the recitals at the beginning of this Agreement.

                 (t)      "Section 13 Event" shall mean any event described in
clause (i), (ii) or (iii) of Section 13(a) hereof.

                 (u)      "Shares Acquisition Date" shall mean the first date
of public announcement (which, for purposes of this definition, shall include,
without limitation, a report filed pursuant to Section 13(d) under the Exchange
Act) by the Company or an Acquiring Person that an Acquiring Person has become
such; provided that, if such person is determined not to have become an
Acquiring Person pursuant to Section 1(a)(ii) hereof, then no Shares
Acquisition Date shall be deemed to have occurred.

                 (v)      "Subsidiary" of any Person shall mean any corporation
or other entity of which an amount of voting securities sufficient to elect a
majority of the directors or Persons having similar authority of such
corporation or other entity is beneficially owned, directly or indirectly, by
such Person, or any corporation or other entity otherwise controlled by such
Person, including, without limitation, ALRT following the exercise of that
certain stock purchase option as set forth in ALRT's Amended and Restated
Certificate of Incorporation, as it may be further amended.

                 (w)      "Total Exercise Price" shall have the meaning set 
forth in Section 4(a) hereof.

                 (x)      "Trading Day" shall have the meaning set forth in
Section 11(d) hereof.

                 (y)      A "Triggering Event" shall be deemed to have occurred
upon any Person (other than the Company, any Subsidiary of the Company, any
employee benefit plan of the Company or any Subsidiary of the Company, or any
entity holding Common Shares for or pursuant to the terms of any such plan),
together with all Affiliates and Associates of such Person, becoming an
Acquiring Person.

         SECTION 2.       APPOINTMENT OF RIGHTS AGENT.  The Company hereby
appoints the Rights Agent to act as agent for the Company and the holders of
the Rights (who, in accordance with Section 3 hereof, shall prior to the
Distribution Date also be the holders of the Common Shares) in accordance with
the terms and conditions hereof, and the Rights Agent hereby accepts such
appointment.  The Company may from time to time appoint such co-Rights Agents
as it may deem necessary or desirable.

         SECTION 3.       ISSUANCE OF RIGHTS CERTIFICATES.

                 (a)      Until the Distribution Date, (i) the Rights will be
evidenced (subject to the provisions of Sections 3(b) and 3(c) hereof) by the
certificates for Common Shares registered in the names of the holders thereof
(which certificates shall also be deemed to be Rights Certificates) and not by
separate Rights Certificates and (ii) the right to receive Rights Certificates
will be transferable only in connection with the transfer of Common





                                      -5-
<PAGE>   9
Shares.  Until the earlier of the Distribution Date or the Expiration Date, the
surrender for transfer of such certificates for Common Shares shall also
constitute the surrender for transfer of the Rights associated with the Common
Shares represented thereby.  As soon as practicable after the Distribution
Date, the Company will prepare and execute, the Rights Agent will countersign,
and the Company will send or cause to be sent (and the Rights Agent will, if
requested, send) by first-class, postage-prepaid mail, to each record holder of
Common Shares as of the close of business on the Distribution Date, at the
address of such holder shown on the records of the Company, a Rights
Certificate, in substantially the form of Exhibit B hereto (a "Rights
Certificate"), evidencing one Right for each Common Share so held, subject to
adjustment as provided herein.  In the event that an adjustment in the number
of Rights per Common Share has been made pursuant to Section 11(a)(i), Section
11(i) or Section 11(p) hereof, then at the time of distribution of the Rights
Certificates, the Company shall make the necessary and appropriate rounding
adjustments (in accordance with Section 14(a) hereof) so that Rights
Certificates representing only whole numbers of Rights are distributed and cash
is paid in lieu of any fractional Rights.  As of the Distribution Date, the
Rights will be evidenced solely by such Rights Certificates and may be
transferred by the transfer of the Rights Certificates as permitted hereby,
separately and apart from any transfer of one or more Common Shares, and the
holders of such Rights Certificates as listed in the records of the Company or
any transfer agent or registrar for the Rights shall be the record holders
thereof.

                 (b)      On the Record Date or as soon as practicable
thereafter, the Company will send a copy of a Summary of Rights in
substantially the form of Exhibit C hereto (the "Summary of Rights"), by
first-class, postage-prepaid mail, to each record holder of Common Shares as of
the close of business on the Record Date, at the address of such holder shown
on the records of the Company.

                 (c)      Unless the Board of Directors by resolution adopted
at or before the time of the issuance (including pursuant to the exercise of
rights under the Company's benefit plans) of any Common Shares specifies to the
contrary, Rights shall be issued in respect of all Common Shares that are
issued after the Record Date but prior to the earlier of the Distribution Date
or the Expiration Date or, in certain circumstances provided in Section 22
hereof, after the Distribution Date.  Certificates representing such Common
Shares shall also be deemed to be certificates for Rights, and shall bear the
following legend:





                                      -6-
<PAGE>   10
                 This certificate also evidences and entitles the holder hereof
                 to certain rights as set forth in a Rights Agreement between
                 LIGAND PHARMACEUTICALS INCORPORATED and WELLS FARGO BANK N.A.
                 as the Rights Agent, dated as of September 13, 1996 (the
                 "Rights Agreement"), the terms of which are hereby
                 incorporated herein by reference and a copy of which is on
                 file at the principal executive offices of Ligand
                 Pharmaceuticals Incorporated.  Under certain circumstances, as
                 set forth in the Rights Agreement, such Rights will be
                 evidenced by separate certificates and will no longer be
                 evidenced by this certificate.  Ligand Pharmaceuticals
                 Incorporated will mail to the holder of this certificate a
                 copy of the Rights Agreement without charge after receipt of a
                 written request therefor.  Under certain circumstances set
                 forth in the Rights Agreement, Rights issued to, or held by,
                 any Person who is, was or becomes an Acquiring Person or any
                 Affiliate or Associate thereof (as such terms are defined in
                 the Rights Agreement), whether currently held by or on behalf
                 of such Person or by any subsequent holder, may become null
                 and void.

With respect to such certificates containing the foregoing legend, until the
earlier of (i) the Distribution Date or (ii) the Expiration Date, the Rights
associated with the Common Shares represented by such certificates shall be
evidenced by such certificates alone, and the surrender for transfer of any
such certificate shall also constitute the transfer of the Rights associated
with the Common Shares represented thereby.  In the event that the Company
purchases or acquires any Common Shares after the Record Date but prior to the
Distribution Date, any Rights associated with such Common Shares shall be
deemed canceled and retired so that the Company shall not be entitled to
exercise any Rights associated with the Common Shares which are no longer
outstanding.

         SECTION 4.       FORM OF RIGHTS CERTIFICATES.

                 (a)      The Rights Certificates (and the forms of election to
purchase Common Shares and of assignment to be printed on the reverse thereof)
shall be substantially in the form of Exhibit B hereto and may have such marks
of identification or designation and such legends, summaries or endorsements
printed thereon as the Company may deem appropriate and as are not inconsistent
with the provisions of this Agreement, or as may be required to comply with any
applicable law or with any rule or regulation made pursuant thereto or with any
rule or regulation of any stock exchange on which the Rights may from time to
time be listed, or to conform to usage.  Subject to the provisions of Section
11 and Section 22 hereof, the Rights Certificates, whenever distributed, shall
be dated as of the Record Date (or in the case of Rights issued with respect to
Common Shares issued by the Company after the Record Date, as of the date of
issuance of such Common Shares) and on their face shall entitle the holders
thereof to purchase such number of one-thousandths of a Preferred Share as
shall be set forth therein at the price set forth therein (such exercise price
per one one-thousandth of a Preferred Share being hereinafter referred to as
the "Purchase Price" and the aggregate exercise price of all Preferred Shares
issuable upon exercise of one Right being hereinafter referred to as the "Total
Exercise Price"), but the number and type of





                                      -7-
<PAGE>   11
securities purchasable upon the exercise of each Right and the Purchase Price
shall be subject to adjustment as provided herein.

                 (b)      Any Rights Certificate issued pursuant to Section
3(a) or Section 22 hereof that represents Rights beneficially owned by: (i) an
Acquiring Person or any Associate or Affiliate of an Acquiring Person, (ii) a
transferee of an Acquiring Person (or of any such Associate or Affiliate) who
becomes a transferee after the Acquiring Person becomes such or (iii) a
transferee of an Acquiring Person (or of any such Associate or Affiliate) who
becomes a transferee prior to or concurrently with the Acquiring Person
becoming such and receives such Rights pursuant to either (A) a transfer
(whether or not for consideration) from the Acquiring Person to holders of
equity interests in such Acquiring Person or to any Person with whom such
Acquiring Person has any continuing agreement, arrangement or understanding
regarding the transferred Rights or (B) a transfer which the Board of Directors
of the Company has determined is part of a plan, arrangement or understanding
which has as a primary purpose or effect avoidance of Section 7(e) hereof, and
any Rights Certificate issued pursuant to Section 6 or Section 11 hereof upon
transfer, exchange, replacement or adjustment of any other Rights Certificate
referred to in this sentence, shall contain (to the extent feasible) the
following legend:

                 The Rights represented by this Rights Certificate are or were
                 beneficially owned by a Person who was or became an Acquiring
                 Person or an Affiliate or Associate of an Acquiring Person (as
                 such terms are defined in the Rights Agreement).  Accordingly,
                 this Rights Certificate and the Rights represented hereby may
                 become null and void in the circumstances specified in Section
                 7(e) of the Rights Agreement.

         SECTION 5.       COUNTERSIGNATURE AND REGISTRATION.

                 (a)      The Rights Certificates shall be executed on behalf
of the Company by its Chairman of the Board, its Chief Executive Officer, its
President or any Vice President, either manually or by facsimile signature, and
by the Secretary or an Assistant Secretary of the Company, either manually or
by facsimile signature, and shall have affixed thereto the Company's seal (if
any) or a facsimile thereof.  The Rights Certificates shall be manually
countersigned by the Rights Agent and shall not be valid for any purpose unless
countersigned.  In case any officer of the Company who shall have signed any of
the Rights Certificates shall cease to be such officer of the Company before
countersignature by the Rights Agent and issuance and delivery by the Company,
such Rights Certificates, nevertheless, may be countersigned by the Rights
Agent and issued and delivered by the Company with the same force and effect as
though the person who signed such Rights Certificates had not ceased to be such
officer of the Company; and any Rights Certificate may be signed on behalf of
the Company by any person who, at the actual date of the execution of such
Rights Certificate, shall be a proper officer of the Company to sign such
Rights Certificate, although at the date of the execution of this Rights
Agreement any such person was not such an officer.

                   (b)      Following the Distribution Date, the Rights Agent 
will keep or cause





                                      -8-
<PAGE>   12
to be kept, at its office designated for such purposes, books for registration
and transfer of the Rights Certificates issued hereunder.  Such books shall
show the names and addresses of the respective holders of the Rights
Certificates, the number of Rights evidenced on its face by each of the Rights
Certificates and the date of each of the Rights Certificates.

         SECTION 6.       TRANSFER, SPLIT UP, COMBINATION AND EXCHANGE OF
RIGHTS CERTIFICATES; MUTILATED, DESTROYED, LOST OR STOLEN RIGHTS CERTIFICATES.

                 (a)      Subject to the provisions of Sections 7(e), 14 and 24
hereof, at any time after the Close of Business on the Distribution Date, and
at or prior to the Close of Business on the Expiration Date, any Rights
Certificate or Rights Certificates may be transferred, split up, combined or
exchanged for another Rights Certificate or Rights Certificates, entitling the
registered holder to purchase a like number of one-thousandths of a Preferred
Share (or, following a Triggering Event, other securities, cash or other
assets, as the case may be) as the Rights Certificate or Rights Certificates
surrendered then entitled such holder to purchase.  Any registered holder
desiring to transfer, split up, combine or exchange any Rights Certificate or
Rights Certificates shall make such request in writing delivered to the Rights
Agent, and shall surrender the Rights Certificate or Rights Certificates to be
transferred, split up, combined or exchanged at the office of the Rights Agent
designated for such purpose.  Neither the Rights Agent nor the Company shall be
obligated to take any action whatsoever with respect to the transfer of any
such surrendered Rights Certificate until the registered holder shall have
completed and signed the certificate contained in the form of assignment on the
reverse side of such Rights Certificate and shall have provided such additional
evidence of the identity of the Beneficial Owner (or former Beneficial Owner)
or Affiliates or Associates thereof as the Company shall reasonably request.
Thereupon the Rights Agent shall, subject to Sections 7(e), 14 and 24 hereof,
countersign and deliver to the person entitled thereto a Rights Certificate or
Rights Certificates, as the case may be, as so requested.  The Company may
require payment of a sum sufficient to cover any tax or governmental charge
that may be imposed in connection with any transfer, split up, combination or
exchange of Rights Certificates.

                 (b)      Upon receipt by the Company and the Rights Agent of
evidence reasonably satisfactory to them of the loss, theft, destruction or
mutilation of a Rights Certificate, and, in case of loss, theft or destruction,
of indemnity or security reasonably satisfactory to them, and, at the Company's
request, reimbursement to the Company and the Rights Agent of all reasonable
expenses incidental thereto, and upon surrender to the Rights Agent and
cancellation of the Rights Certificate if mutilated, the Company will make and
deliver a new Rights Certificate of like tenor to the Rights Agent for delivery
to the registered holder in lieu of the Rights Certificate so lost, stolen,
destroyed or mutilated.

         SECTION 7.       EXERCISE OF RIGHTS; PURCHASE PRICE; EXPIRATION DATE
OF RIGHTS.

                 (a)      Subject to Sections 7(e), 23(b) and 24(b) hereof, the
registered holder of any Rights Certificate may exercise the Rights evidenced
thereby (except as otherwise provided herein) in whole or in part at any time
after the Distribution Date upon surrender of the Rights Certificate, with the
form of election to purchase on the reverse side thereof





                                      -9-
<PAGE>   13
duly executed, to the Rights Agent at the office of the Rights Agent designated
for such purpose, together with payment of the Purchase Price for each
one-thousandth of a Preferred Share as to which the Rights are exercised, at or
prior to the Expiration Date.

                 (b)      The Purchase Price for each one-thousandth of a
Preferred Share issuable pursuant to the exercise of a Right shall initially be
One Hundred Dollars ($100.00), shall be subject to adjustment from time to time
as provided in Sections 11 and 13 hereof and shall be payable in lawful money
of the United States of America in accordance with paragraph (c) below.

                 (c)      Upon receipt of a Rights Certificate representing
exercisable Rights, with the form of election to purchase duly executed,
accompanied by payment of the Purchase Price for the number of one-thousandths
of a Preferred Share (or other securities or property, as the case may be) to
be purchased and an amount equal to any applicable transfer tax required to be
paid by the holder of such Rights Certificate in accordance with Section 9
hereof in cash, or by certified check or cashier's check payable to the order
of the Company, the Rights Agent shall, subject to Section 20(k) hereof,
thereupon promptly (i) (A) requisition from any transfer agent of the Preferred
Shares (or make available, if the Rights Agent is the transfer agent for the
Preferred Shares) a certificate or certificates for the number of one-
thousandths of a Preferred Share to be purchased and the Company hereby
irrevocably authorizes its transfer agent to comply with all such requests or
(B) if the Company shall have elected to deposit the total number of
one-thousandths of a Preferred Share issuable upon exercise of the Rights
hereunder with a depositary agent, requisition from the depositary agent of
depositary receipts representing such number of one- thousandths of a Preferred
Share as are to be purchased (in which case certificates for the Preferred
Shares represented by such receipts shall be deposited by the transfer agent
with the depositary agent) and the Company hereby directs the depositary agent
to comply with such request, (ii) when appropriate, requisition from the
Company the amount of cash to be paid in lieu of issuance of fractional shares
in accordance with Section 14 hereof, (iii) after receipt of such certificates
or depositary receipts, cause the same to be delivered to or upon the order of
the registered holder of such Rights Certificate, registered in such name or
names as may be designated by such holder and (iv) when appropriate, after
receipt thereof, deliver such cash to or upon the order of the registered
holder of such Rights Certificate.  The payment of the Purchase Price (as such
amount may be reduced (including to zero) pursuant to Section 11(a)(iv) hereof)
may be made in cash or by certified bank check or bank draft payable to the
order of the Company.  In the event that the Company is obligated to issue
other securities of the Company, pay cash and/or distribute other property
pursuant to Section 11(a) hereof, the Company will make all arrangements
necessary so that such other securities, cash and/or other property are
available for distribution by the Rights Agent, if and when appropriate.

                 (d)      In case the registered holder of any Rights
Certificate shall exercise less than all the Rights evidenced thereby, a new
Rights Certificate evidencing Rights equivalent to the Rights remaining
unexercised shall be issued by the Rights Agent to the registered holder of
such Rights Certificate or to his or her duly authorized assigns, subject to
the





                                      -10-
<PAGE>   14
provisions of Section 14 hereof.

                 (e)      Notwithstanding anything in this Agreement to the
contrary, from and after the first occurrence of a Triggering Event or a
Section 13 Event, any Rights beneficially owned by (i) an Acquiring Person or
an Associate or Affiliate of an Acquiring Person, (ii) a transferee of an
Acquiring Person (or of any such Associate or Affiliate) who becomes a
transferee after the Acquiring Person becomes such (a "Post Transferee"), (iii)
a transferee of an Acquiring Person (or of any such Associate or Affiliate) who
becomes a transferee prior to or concurrently with the Acquiring Person
becoming such and receives such Rights pursuant to either (A) a transfer
(whether or not for consideration) from the Acquiring Person to holders of
equity interests in such Acquiring Person or to any Person with whom the
Acquiring Person has any continuing agreement, arrangement or understanding
regarding the transferred Rights or (B) a transfer which the Board of Directors
of the Company has determined is part of a plan, arrangement or understanding
which has as a primary purpose or effect the avoidance of this Section 7(e) (a
"Prior Transferee") or (iv) any subsequent transferee receiving transferred
Rights from a Post Transferee or a Prior Transferee, either directly or through
one or more intermediate transferees, shall become null and void without any
further action and no holder of such Rights shall have any rights whatsoever
with respect to such Rights, whether under any provision of this Agreement or
otherwise.  The Company shall use all reasonable efforts to insure that the
provisions of this Section 7(e) and Section 4(b) hereof are complied with, but
shall have no liability to any holder of Rights Certificates or to any other
Person as a result of its failure to make any determinations with respect to an
Acquiring Person or any of such Acquiring Person's Affiliates, Associates or
transferees hereunder.

                 (f)      Notwithstanding anything in this Agreement to the
contrary, neither the Rights Agent nor the Company shall be obligated to
undertake any action with respect to a registered holder upon the occurrence of
any purported exercise as set forth in this Section 7 unless such registered
holder shall have (i) completed and signed the certificate contained in the
form of election to purchase set forth on the reverse side of the Rights
Certificate surrendered for such exercise and (ii) provided such additional
evidence of the identity of the Beneficial Owner (or former Beneficial Owner)
or Affiliates or Associates thereof as the Company shall reasonably request.

         SECTION 8.      CANCELLATION AND DESTRUCTION OF RIGHTS CERTIFICATES.
All Rights Certificates surrendered for the purpose of exercise, transfer,
split up, combination or exchange shall, if surrendered to the Company or to
any of its agents, be delivered to the Rights Agent for cancellation or in
canceled form, or, if surrendered to the Rights Agent, shall be canceled by it,
and no Rights Certificates shall be issued in lieu thereof except as expressly
permitted by any of the provisions of this Agreement.  The Company shall
deliver to the Rights Agent for cancellation and retirement, and the Rights
Agent shall so cancel and retire, any other Rights Certificate purchased or
acquired by the Company otherwise than upon the exercise thereof.  The Rights
Agent shall deliver all canceled Rights Certificates to the Company, or shall,
at the written request of the Company, destroy such canceled Rights
Certificates, and in such case shall deliver a certificate of destruction
thereof to the Company.





                                      -11-
<PAGE>   15
         SECTION 9.      RESERVATION AND AVAILABILITY OF PREFERRED SHARES.

                 (a)      The Company covenants and agrees that it will use its
best efforts to cause to be reserved and kept available out of and to the
extent of its authorized and unissued shares of Preferred Stock not reserved
for another purpose (and, following the occurrence of a Triggering Event, out
of its authorized and unissued shares of Common Stock and/or other securities),
the number of Preferred Shares (and, following the occurrence of the Triggering
Event, Common Stock and/or other securities) that will be sufficient to permit
the exercise in full of all outstanding Rights.

                 (b)      If the Company shall hereafter list any of its
Preferred Shares on a national securities exchange, then so long as the
Preferred Shares (and, following the occurrence of a Triggering Event, Common
Shares and/or other securities) issuable and deliverable upon exercise of the
Rights may be listed on such exchange, the Company shall use its best efforts
to cause, from and after such time as the Rights become exercisable (but only
to the extent that it is reasonably likely that the Rights will be exercised),
all shares reserved for such issuance to be listed on such exchange upon
official notice of issuance upon such exercise.

                 (c)      The Company shall use its best efforts to (i) file,
as soon as practicable following the earliest date after the first occurrence
of a Triggering Event in which the consideration to be delivered by the Company
upon exercise of the Rights has been determined in accordance with Section
11(a)(iv) hereof, or as soon as is required by law following the Distribution
Date, as the case may be, a registration statement under the Securities Act of
1933, as amended (the "Securities Act"), with respect to the securities
purchasable upon exercise of the Rights on an appropriate form, (ii) cause such
registration statement to become effective as soon as practicable after such
filing and (iii) cause such registration statement to remain effective (with a
prospectus at all times meeting the requirements of the Securities Act) until
the earlier of (A) the date as of which the Rights are no longer exercisable
for such securities and (B) the date of expiration of the Rights.  The Company
may temporarily suspend, for a period not to exceed ninety (90) days after the
date set forth in clause (i) of the first sentence of this Section 9(c), the
exercisability of the Rights in order to prepare and file such registration
statement and permit it to become effective.  Upon any such suspension, the
Company shall issue a public announcement stating, and notify the Rights Agent,
that the exercisability of the Rights has been temporarily suspended, as well
as a public announcement and notification to the Rights Agent at such time as
the suspension is no longer in effect.  The Company will also take such action
as may be appropriate under, or to ensure compliance with, the securities or
"blue sky" laws of the various states in connection with the exercisability of
the Rights.  Notwithstanding any provision of this Agreement to the contrary,
the Rights shall not be exercisable in any jurisdiction, unless the requisite
qualification in such jurisdiction shall have been obtained, or an exemption
therefrom shall be available, and until a registration statement has been
declared effective.

                 (d)      The Company covenants and agrees that it will take
all such action as may be necessary to ensure that all Preferred Shares
delivered upon exercise of Rights shall,





                                      -12-
<PAGE>   16
at the time of delivery of the certificates for such Preferred Shares (subject
to payment of the Purchase Price), be duly and validly authorized and issued
and fully paid and nonassessable shares.

                 (e)      The Company further covenants and agrees that it will
pay when due and payable any and all federal and state transfer taxes and
charges which may be payable in respect of the original issuance or delivery of
the Rights Certificates or of any Preferred Shares upon the exercise of Rights.
The Company shall not, however, be required to pay any transfer tax which may
be payable in respect of any transfer or delivery of Rights Certificates to a
person other than, or the issuance or delivery of certificates or depositary
receipts for the Preferred Shares in a name other than that of, the registered
holder of the Rights Certificate evidencing Rights surrendered for exercise or
to issue or to deliver any certificates or depositary receipts for Preferred
Shares upon the exercise of any Rights until any such tax shall have been paid
(any such tax being payable by the holder of such Rights Certificate at the
time of surrender) or until it has been established to the Company's
satisfaction that no such tax is due.

         SECTION 10.      PREFERRED SHARES RECORD DATE.  Each person in whose
name any certificate for a number of one-thousandths of a Preferred Share is
issued upon the exercise of Rights shall for all purposes be deemed to have
become the holder of record of Preferred Shares represented thereby on, and
such certificate shall be dated, the date upon which the Rights Certificate
evidencing such Rights was duly surrendered and payment of the Purchase Price
multiplied by the number of one-thousandths of a Preferred Share with respect
to which the Rights have been exercised (and any applicable transfer taxes) was
made; provided, however, that if the date of such surrender and payment is a
date upon which the Preferred Shares transfer books of the Company are closed,
such person shall be deemed to have become the record holder of such shares on,
and such certificate shall be dated, the next succeeding Business Day on which
the Preferred Shares transfer books of the Company are open.  Prior to the
exercise of the Rights evidenced thereby, the holder of a Rights Certificate
shall not be entitled to any rights of a holder of Preferred Shares for which
the Rights shall be exercisable, including, without limitation, the right to
vote, to receive dividends or other distributions or to exercise any preemptive
rights, and shall not be entitled to receive any notice of any proceedings of
the Company, except as provided herein.

         SECTION 11.      ADJUSTMENT OF PURCHASE PRICE, NUMBER OF SHARES OR
NUMBER OF RIGHTS.  The Purchase Price, the number and kind of shares or other
property covered by each Right and the number of Rights outstanding are subject
to adjustment from time to time as provided in this Section 11.

                 (a)      (i)     In the event the Company shall at any time
after the date of this Agreement (A) declare a dividend on the Common Shares
payable in Common Shares, (B) subdivide the outstanding Common Shares, (C)
combine the outstanding Common Shares (by reverse stock split or otherwise)
into a smaller number of Common Shares, or (D) issue any shares of its capital
stock in a reclassification of the Common Shares (including any such
reclassification in connection with a consolidation or merger in which the
Company is the continuing or surviving corporation), then, in each such event,
except as otherwise provided





                                      -13-
<PAGE>   17
in this Section 11(a) and Section 7(e) hereof: (1) each of the Rights
outstanding at the time of the record date for such dividend or the effective
date of such subdivision, combination or reclassification shall be
proportionately adjusted to that number of Rights (calculated to the nearest
one ten-thousandth (1/10,000) of a Right) equal to a fraction (the "Exchange
Ratio"), the numerator of which shall be the total number of Common Shares or
shares of capital stock issued in such reclassification of the Common Shares
outstanding immediately following such time and the denominator of which shall
be the total number of Common Shares outstanding immediately prior to such
time, and the number of Rights that shall thereafter be issued with respect to
each Common Share or share of such other capital stock that shall become
outstanding thereafter prior to the Distribution Date shall be equal to the
total number of outstanding Rights immediately after such event (as adjusted
pursuant to this clause (1)) divided by the total number of outstanding Common
Shares or shares of such other capital stock immediately after such event
(subject to further adjustment pursuant to the provisions of this Agreement);
(2) the Purchase Price in effect at the time of the record date for such
dividend or of the effective date of such subdivision, combination or
reclassification shall be adjusted so that the Purchase Price thereafter shall
equal the result obtained by dividing the Purchase Price in effect immediately
prior to such time by the Exchange Ratio; provided, however, that in no event
shall the consideration to be paid upon the exercise of one Right be less than
the aggregate par value of the shares of capital stock of the Company issuable
upon exercise of such Right; and (3) the number of Preferred Shares or shares
of such other capital stock issuable upon the exercise of each Right shall
remain unchanged immediately after such event, but, in the event of a
reclassification, the kind of shares issuable upon the exercise of each Right
immediately after such reclassification shall be appropriately adjusted.  If an
event occurs which would require an adjustment under both this Section 11(a)(i)
and Section 11(a)(ii) hereof, the adjustment provided for in this Section
11(a)(i) shall be in addition to, and shall be made prior to, any adjustment
required pursuant to Section 11(a)(ii) hereof.

                          (ii)    Subject to Section 24 of this Agreement, in
the event a Triggering Event shall have occurred, then promptly following such
Triggering Event, proper provision shall be made so that each holder of a
Right, except as provided in Section 7(e) hereof, shall thereafter have the
right to receive for each Right, upon exercise thereof in accordance with the
terms of this Agreement and payment of the then-current Total Exercise Price,
in lieu of a number of one-thousandths of a Preferred Share, such number of
Common Shares of the Company as shall equal the result obtained by multiplying
the then-current Purchase Price by the then number of one-thousandths of a
Preferred Share for which a Right was exercisable (or would have been
exercisable if the Distribution Date had occurred) immediately prior to the
first occurrence of a Triggering Event, and dividing that product by 50% of the
current per share market price (determined pursuant to Section 11(d) hereof)
for Common Shares on the date of occurrence of the Triggering Event (such
number of shares being hereinafter referred to as the "Adjustment Shares").

                          (iii)   The right to buy Common Shares of the Company
pursuant to Section 11(a)(ii) hereof shall not arise as a result of any Person
becoming an Acquiring Person through an acquisition of Common Shares pursuant
to a Permitted Offer.





                                      -14-
<PAGE>   18
                          (iv)    In lieu of issuing Common Shares in
accordance with Section 11(a)(ii) hereof, the Company may, if the Board of
Directors determines that such action is necessary or appropriate and not
contrary to the interest of holders of Rights (and, in the event that the
number of Common Shares which are authorized by the Company's Articles of
Incorporation but not outstanding or reserved for issuance for purposes other
than upon exercise of the Rights are not sufficient to permit the exercise in
full of the Rights, or if any necessary regulatory approval for such issuance
has not been obtained by the Company, the Company shall): (A) determine the
excess of (1) the value of the Common Shares issuable upon the exercise of a
Right (the "Current Value") over (2) the Purchase Price (such excess, the
"Spread") and (B) with respect to each Right, make adequate provision to
substitute for such Common Shares, upon exercise of the Rights, (1) cash, (2) a
reduction in the Purchase Price, (3) other equity securities of the Company
(including, without limitation, shares or units of shares of any series of
preferred stock which the Board of Directors of the Company has deemed to have
the same value as Common Shares (such shares or units of shares of preferred
stock are herein called "common stock equivalents")), except to the extent that
the Company has not obtained any necessary stockholder or regulatory approval
for such issuance, (4) debt securities of the Company, except to the extent
that the Company has not obtained any necessary stockholder or regulatory
approval for such issuance, (5) other assets or (6) any combination of the
foregoing, having an aggregate value equal to the Current Value, where such
aggregate value has been determined by the Board of Directors of the Company
based upon the advice of a nationally recognized investment banking firm
selected by the Board of Directors of the Company; provided, however, if the
Company shall not have made adequate provision to deliver value pursuant to
clause (B) above within thirty (30) days following the later of (x) the first
occurrence of a Triggering Event and (y) the date on which the Company's right
of redemption pursuant to Section 23(a) expires (the later of (x) and (y) being
referred to herein as the "Section 11(a)(ii) Trigger Date"), then the Company
shall be obligated to deliver, upon the surrender for exercise of a Right and
without requiring payment of the Purchase Price, Common Shares (to the extent
available), except to the extent that the Company has not obtained any
necessary stockholder or regulatory approval for such issuance, and then, if
necessary, cash, which shares and/or cash have an aggregate value equal to the
Spread.  If the Board of Directors of the Company shall determine in good faith
that it is likely that sufficient additional Common Shares could be authorized
for issuance upon exercise in full of the Rights or that any necessary
regulatory approval for such issuance will be obtained, the thirty (30) day
period set forth above may be extended to the extent necessary, but not more
than ninety (90) days after the Section 11(a)(ii) Trigger Date, in order that
the Company may seek stockholder approval for the authorization of such
additional shares or take action to obtain such regulatory approval (such
period, as it may be extended, the "Substitution Period").  To the extent that
the Company determines that some action need be taken pursuant to the first
and/or second sentences of this Section 11(a)(iv), the Company (x) shall
provide, subject to Section 7(e) hereof, that such action shall apply uniformly
to all outstanding Rights and (y) may suspend the exercisability of the Rights
until the expiration of the Substitution Period in order to seek any
authorization of additional shares, to take any action to obtain any required
regulatory approval and/or to decide the appropriate form of distribution to be
made pursuant to such first sentence and to determine the value thereof.  In
the event of any such suspension, the Company shall issue a public announcement
stating that the exercisability





                                      -15-
<PAGE>   19
of the Rights has been temporarily suspended, as well as a public announcement
at such time as the suspension is no longer in effect.  For purposes of this
Section 11(a)(iv), the value of the Common Shares shall be the current per
share market price (as determined pursuant to Section 11(d) hereof) of the
Common Shares on the Section 11(a)(ii) Trigger Date and the value of any
"common stock equivalent" shall be deemed to have the same value as the Common
Shares on such date.

                 (b)      In case the Company shall, at any time after the date
of this Agreement, fix a record date for the issuance of rights, options or
warrants to all holders of Common Shares or of any class or series of
Equivalent Shares entitling such holders (for a period expiring within
forty-five (45) calendar days after such record date) to subscribe for or
purchase Common Shares or Equivalent Shares or securities convertible into
Common Shares or Equivalent Shares at a price per share (or having a conversion
price per share, if a security convertible into Common Shares or Equivalent
Shares) less than the then current per share market price of the Common Shares
or Equivalent Shares (as defined in Section 11(d)) on such record date, then,
in each such case, the Purchase Price to be in effect after such record date
shall be determined by multiplying the Purchase Price in effect immediately
prior to such record date by a fraction, the numerator of which shall be the
number of Common Shares and Equivalent Shares (if any) outstanding on such
record date, plus the number of Common Shares or Equivalent Shares, as the case
may be, which the aggregate offering price of the total number of Common Shares
or Equivalent Shares, as the case may be, so to be offered (and/or the
aggregate initial conversion price of the convertible securities so to be
offered) would purchase at such current market price, and the denominator of
which shall be the number of Common Shares and Equivalent Shares (if any)
outstanding on such record date, plus the number of additional Common Shares or
Equivalent Shares, as the case may be, to be offered for subscription or
purchase (or into which the convertible securities so to be offered are
initially convertible).  In case such subscription price may be paid in a
consideration part or all of which shall be in a form other than cash, the
value of such consideration shall be as determined in good faith by the Board
of Directors of the Company, whose determination shall be described in a
statement filed with the Rights Agent and shall be binding on the Rights Agent
and the holders of the Rights.  Common Shares and Equivalent Shares owned by or
held for the account of the Company shall not be deemed outstanding for the
purpose of any such computation.  Such adjustment shall be made successively
whenever such a record date is fixed, and in the event that such rights,
options or warrants are not so issued, the Purchase Price shall be adjusted to
be the Purchase Price which would then be in effect if such record date had not
been fixed.

                 (c)      In case the Company shall, at any time after the date
of this Agreement, fix a record date for the making of a distribution to all
holders of the Common Shares or of any class or series of Equivalent Shares
(including any such distribution made in connection with a consolidation or
merger in which the Company is the continuing or surviving corporation) of
evidences of indebtedness or assets (other than a regular quarterly cash
dividend, if any, or a dividend payable in Common Shares) or subscription
rights, options or warrants (excluding those referred to in Section 11(b)),
then, in each such case, the Purchase Price to be in effect after such record
date shall be determined by multiplying





                                      -16-
<PAGE>   20
the Purchase Price in effect immediately prior to such record date by a
fraction, the numerator of which shall be the current market price (as
determined pursuant to Section 11(d) hereof) of a Common Share or an Equivalent
Share on such record date, less the fair market value (as determined in good
faith by the Board of Directors of the Company, whose determination shall be
described in a statement filed with the Rights Agent) of the portion of the
cash, assets or evidences of indebtedness so to be distributed or of such
subscription rights or warrants applicable to a Common Share or Equivalent
Share, as the case may be, and the denominator of which shall be such current
market price (as determined pursuant to Section 11(d) hereof) of a Common Share
or Equivalent Share on such record date.  Such adjustments shall be made
successively whenever such a record date is fixed, and in the event that such
distribution is not so made, the Purchase Price shall be adjusted to be the
Purchase Price which would have been in effect if such record date had not been
fixed.

                 (d)      For the purpose of any computation hereunder, other
than computations made pursuant to Section 11(a)(iv) hereof, the "current per
share market price" of any security (a "Security" for the purpose of this
Section 11(d)) on any date shall be deemed to be the average of the daily
closing prices per share of such Security for the thirty (30) consecutive
Trading Days (as such term is hereinafter defined) immediately prior to such
date, and for purposes of computations made pursuant to Section 11(a)(iv)
hereof, the "current per share market price" of any Security on any date shall
be deemed to be the average of the daily closing prices per share of such
Security for the ten (10) consecutive Trading Days immediately prior to such
date; provided, however, that in the event that the current per share market
price of the Security is determined during a period following the announcement
by the issuer of such Security of (i) a dividend or distribution on such
Security payable in shares of such Security or securities convertible into such
shares or (ii) any subdivision, combination or reclassification of such
Security, and prior to the expiration of the requisite thirty (30) Trading Day
or ten (10) Trading Day period, after the ex-dividend date for such dividend or
distribution, or the record date for such subdivision, combination or
reclassification, then, and in each such case, the current per share market
price shall be appropriately adjusted to reflect the current market price per
share equivalent of such Security.  The closing price for each day shall be the
last sale price, regular way, or, in case no such sale takes place on such day,
the average of the closing bid and asked prices, regular way, in either case as
reported in the principal consolidated transaction reporting system with
respect to securities listed or admitted to trading on the New York Stock
Exchange or, if the Security is not listed or admitted to trading on the New
York Stock Exchange, as reported in the principal consolidated transaction
reporting system with respect to securities listed on the principal national
securities exchange on which the Security is listed or admitted to trading or,
if the Security is not listed or admitted to trading on any national securities
exchange, the last sale price or, if such last sale price is not reported, the
average of the high bid and low asked prices in the over-the-counter market, as
reported by the National Association of Securities Dealers, Inc.  Automated
Quotations System ("Nasdaq") or such other system then in use, or, if on any
such date the Security is not quoted by any such organization, the average of
the closing bid and asked prices as furnished by a professional market maker
making a market in the Security selected by the Board of Directors of the
Company.  If on any such date no market maker is making a market in the Common
Shares, the fair value of such shares on such date as determined in





                                      -17-
<PAGE>   21
good faith by the Board of Directors of the Company shall be used.  The term
"Trading Day" shall mean a day on which the principal national securities
exchange on which the Security is listed or admitted to trading is open for the
transaction of business or, if the Security is not listed or admitted to
trading on any national securities exchange, a Business Day.  If the Common
Shares are not publicly held or so listed or traded, "current per share market
price" shall mean the fair value per share as determined in good faith by the
Board of Directors of the Company, whose determination shall be described in a
statement filed with the Rights Agent and shall be conclusive for all purposes.

                 (e)      Anything herein to the contrary notwithstanding, no
adjustment in the Purchase Price shall be required unless such adjustment would
require an increase or decrease of at least 1% in the Purchase Price; provided,
however, that any adjustments which by reason of this Section 11(e) are not
required to be made shall be carried forward and taken into account in any
subsequent adjustment.  All calculations under this Section 11 shall be made to
the nearest cent or to the nearest ten-thousandth of a Common Share or other
share or one hundred-thousandth of a Preferred Share, as the case may be.
Notwithstanding the first sentence of this Section 11(e), any adjustment
required by this Section 11 shall be made no later than the earlier of (i)
three (3) years from the date of the transaction which requires such adjustment
or (ii) the Expiration Date.

                 (f)      If as a result of an adjustment made pursuant to
Section 11(a) or 13(a) hereof, the holder of any Right thereafter exercised
shall become entitled to receive any shares of capital stock other than
Preferred Shares, thereafter the number of such other shares so receivable upon
exercise of any Right and if required, the Purchase Price thereof, shall be
subject to adjustment from time to time in a manner and on terms as nearly
equivalent as practicable to the provisions with respect to the Common Shares
contained in Sections 11(a), (b), (c), (e), (h), (i), (j), (k), (l) and (m),
and the provisions of Sections 7, 9, 10, 13 and 14 with respect to the
Preferred Shares shall apply on like terms to any such other shares.

                 (g)      All Rights originally issued by the Company
subsequent to any adjustment made to the Purchase Price hereunder shall
evidence the right to purchase, at the adjusted Purchase Price, the number of
one-thousandths of a Preferred Share purchasable from time to time hereunder
upon exercise of the Rights, all subject to further adjustment as provided
herein.

                 (h)      Unless the Company shall have exercised its election
as provided in Section 11(i), upon each adjustment of the Purchase Price as a
result of the calculations made in Section 11(b), each Right outstanding
immediately prior to the making of such adjustment shall thereafter evidence
the right to purchase, at the adjusted Purchase Price, that number of Preferred
Shares (calculated to the nearest one hundred-thousandth of a share) obtained
by (i) multiplying (x) the number of Preferred Shares covered by a Right
immediately prior to this adjustment, by (y) the Purchase Price in effect
immediately prior to such adjustment of the Purchase Price, and (ii) dividing
the product so obtained by the Purchase Price in effect immediately after such
adjustment of the Purchase Price.





                                      -18-
<PAGE>   22
                 (i)      The Company may elect on or after the date of any
adjustment of the Purchase Price as a result of the calculations made in
Section 11(b) to adjust the number of Rights, in substitution for any
adjustment in the number of Preferred Shares purchasable upon the exercise of a
Right.  Each of the Rights outstanding after such adjustment of the number of
Rights shall be exercisable for the number of one-thousandths of a Preferred
Share for which a Right was exercisable immediately prior to such adjustment.
Each Right held of record prior to such adjustment of the number of Rights
shall become that number of Rights (calculated to the nearest one
hundred-thousandth) obtained by dividing the Purchase Price in effect
immediately prior to adjustment of the Purchase Price by the Purchase Price in
effect immediately after adjustment of the Purchase Price.  The Company shall
make a public announcement of its election to adjust the number of Rights,
indicating the record date for the adjustment, and, if known at the time, the
amount of the adjustment to be made.  This record date may be the date on which
the Purchase Price is adjusted or any day thereafter, but, if the Rights
Certificates have been issued, shall be at least ten (10) days later than the
date of the public announcement.  If Rights Certificates have been issued, upon
each adjustment of the number of Rights pursuant to this Section 11(i), the
Company shall, as promptly as practicable, cause to be distributed to holders
of record of Rights Certificates on such record date Rights Certificates
evidencing, subject to Section 14 hereof, the additional Rights to which such
holders shall be entitled as a result of such adjustment, or, at the option of
the Company, shall cause to be distributed to such holders of record in
substitution and replacement for the Rights Certificates held by such holders
prior to the date of adjustment, and upon surrender thereof, if required by the
Company, new Rights Certificates evidencing all the Rights to which such
holders shall be entitled after such adjustment.  Rights Certificates so to be
distributed shall be issued, executed and countersigned in the manner provided
for herein (and may bear, at the option of the Company, the adjusted Purchase
Price) and shall be registered in the names of the holders of record of Rights
Certificates on the record date specified in the public announcement.

                 (j)      Irrespective of any adjustment or change in the
Purchase Price or the number of Preferred Shares issuable upon the exercise of
the Rights, the Rights Certificates theretofore and thereafter issued may
continue to express the Purchase Price per one one- thousandth of a Preferred
Share and the number of one-thousandths of a Preferred Share which were
expressed in the initial Rights Certificates issued hereunder.

                 (k)      Before taking any action that would cause an
adjustment reducing the Purchase Price below the par or stated value, if any,
of the number of one-thousandths of a Preferred Share issuable upon exercise of
the Rights, the Company shall take any corporate action which may, in the
opinion of its counsel, be necessary in order that the Company may validly and
legally issue as fully paid and nonassessable shares such number of
one-thousandths of a Preferred Share at such adjusted Purchase Price.

                 (l)      In any case in which this Section 11 shall require
that an adjustment in the Purchase Price be made effective as of a record date
for a specified event, the Company may elect to defer until the occurrence of
such event the issuing to the holder of any Right exercised after such record
date of the number of one-thousandths of a Preferred Share and other capital
stock or securities of the Company, if any, issuable upon such





                                      -19-
<PAGE>   23
exercise over and above the number of one-thousandths of a Preferred Share and
other capital stock or securities of the Company, if any, issuable upon such
exercise on the basis of the Purchase Price in effect prior to such adjustment;
provided, however, that the Company shall deliver to such holder a due bill or
other appropriate instrument evidencing such holder's right to receive such
additional shares (fractional or otherwise) upon the occurrence of the event
requiring such adjustment.

                 (m)      Anything in this Section 11 to the contrary
notwithstanding, prior to the Distribution Date, the Company shall be entitled
to make such reductions in the Purchase Price, in addition to those adjustments
expressly required by this Section 11, as and to the extent that it in its sole
discretion shall determine to be advisable in order that any (i) consolidation
or subdivision of the Preferred or Common Shares, (ii) issuance wholly for cash
of any Preferred or Common Shares at less than the current market price, (iii)
issuance wholly for cash of Preferred or Common Shares or securities which by
their terms are convertible into or exchangeable for Preferred or Common
Shares, (iv) stock dividends or (v) issuance of rights, options or warrants
referred to in this Section 11, hereafter made by the Company to holders of its
Preferred or Common Shares shall not be taxable to such stockholders.

                 (n)      The Company covenants and agrees that it shall not,
at any time after the Distribution Date, effect or permit to occur any
Triggering Event or Section 13 Event, if (i) at the time or immediately after
such Triggering Event or Section 13 Event there are any rights, warrants or
other instruments or securities outstanding or agreements in effect which would
substantially diminish or otherwise eliminate the benefits intended to be
afforded by the Rights or (ii) prior to, simultaneously with or immediately
after such Section 13 Event, the stockholders of the Person who constitutes, or
would constitute, the "Principal Party" for purposes of Section 13(b) hereof
shall have received a distribution of Rights previously owned by such Person or
any of its Affiliates and Associates.

                 (o)      The Company covenants and agrees that, after the
Distribution Date, it will not, except as permitted by Sections 23, 24 or 27
hereof, take (or permit to be taken) any action if at the time such action is
taken it is reasonably foreseeable that such action will diminish substantially
or otherwise eliminate the benefits intended to be afforded by the Rights.

                 (p)      Anything in this Agreement to the contrary
notwithstanding, in the event the Company shall at any time after the date of
this Agreement (A) declare a dividend on the Preferred Shares payable in
Preferred Shares, (B) subdivide the outstanding Preferred Shares, (C) combine
the outstanding Preferred Shares (by reverse stock split or otherwise) into a
smaller number of Preferred Shares, or (D) issue any shares of its capital
stock in a reclassification of the Preferred Shares (including any such
reclassification in connection with a consolidation or merger in which the
Company is the continuing or surviving corporation), then, in each such event,
except as otherwise provided in this Section 11 and Section 7(e) hereof: (1)
each of the Rights outstanding at the time of the record date for such dividend
or the effective date of such subdivision, combination or reclassification
shall be proportionately adjusted to that number of Rights (calculated to the
nearest one





                                      -20-
<PAGE>   24
ten-thousandth (1/10,000) of a Right) equal to a fraction (the "Exchange
Fraction"), the numerator of which shall be the total number of Preferred
Shares or shares of capital stock issued in such reclassification of the
Preferred Shares outstanding immediately following such time and the
denominator of which shall be the total number of Preferred Shares outstanding
immediately prior to such time, and the number of Rights that shall thereafter
be issued with respect to each Common Share or share of other capital stock
that shall be issued in a reclassification of the Common Shares prior to the
Distribution Date shall be equal to the total number of outstanding Rights
immediately after such event (as adjusted pursuant to this clause (1)) divided
by the total number of outstanding Common Shares or shares of such other
capital stock immediately after such event (subject to further adjustment
pursuant to the provisions of this Agreement); (2) the Purchase Price in effect
at the time of the record date for such dividend or of the effective date of
such subdivision, combination or reclassification shall be adjusted so that the
Purchase Price thereafter shall equal the result obtained by dividing the
Purchase Price in effect immediately prior to such time by the Exchange
Fraction; provided, however, that in no event shall the consideration to be
paid upon the exercise of one Right be less than the aggregate par value of the
shares of capital stock of the Company issuable upon exercise of such Right;
and (3) the number of one-thousandths of a Preferred Share or share of such
other capital stock issuable upon the exercise of each Right shall remain
unchanged immediately after such event, but, in the event of a
reclassification, the kind of shares issuable upon the exercise of each Right
immediately after such reclassification shall be adjusted to be the kind of
shares of such other capital stock issued in such reclassification, rather than
Preferred Shares.

         SECTION 12.      CERTIFICATE OF ADJUSTED PURCHASE PRICE OR NUMBER OF
SHARES. Whenever an adjustment is made as provided in Sections 11 and 13
hereof, the Company shall promptly (a) prepare a certificate setting forth such
adjustment and a brief statement of the facts accounting for such adjustment,
(b) file with the Rights Agent and with each transfer agent for the Preferred
Shares a copy of such certificate and (c) mail a brief summary thereof to each
holder of a Rights Certificate in accordance with Section 26 hereof.
Notwithstanding the foregoing sentence, the failure of the Company to make such
certification or give such notice shall not affect the validity of such
adjustment or the force or effect of the requirement for such adjustment.   The
Rights Agent shall be fully protected in relying on any such certificate and on
any adjustment contained therein and shall not be deemed to have knowledge of
such adjustment unless and until it shall have received such certificate.

         SECTION 13.      CONSOLIDATION, MERGER OR SALE OR TRANSFER OF ASSETS
OR EARNING POWER.

                 (a)      In the event that, following the Shares Acquisition
Date, directly or indirectly:

                          (i)     the Company shall consolidate with, or merge
with and into, any other Person (other than a Subsidiary of the Company in a
transaction the principal purpose of which is to change the state of
incorporation of the Company or which complies with Section 11(o) hereof);





                                      -21-
<PAGE>   25
                          (ii)    any Person (other than a Subsidiary of the
Company in a transaction that complies with Section 11(o) hereof) shall
consolidate with the Company, or merge with and into the Company and the
Company shall be the continuing or surviving corporation of such consolidation
or merger; or

                          (iii)   the Company shall sell or otherwise transfer
(or one or more of its Subsidiaries shall sell or otherwise transfer), in one
or more transactions, assets or earning power aggregating 50% or more of the
assets or earning power of the Company and its Subsidiaries (taken as a whole)
to any other Person or Persons (other than the Company or one or more of its
wholly owned Subsidiaries in one or more transactions, each of which complies
with Section 11(o) hereof), then, and in each such case, proper provision shall
be made so that

                                  (A)      each holder of a Right (except as
otherwise provided herein) shall thereafter have the right to receive, upon the
exercise thereof in accordance with the terms of this Agreement, such number of
validly authorized and issued, fully paid and nonassessable Common Shares of
the Principal Party (as hereinafter defined), free of any liens, encumbrances,
rights of first refusal or other adverse claims, as shall be equal to the
result obtained by (1) multiplying the then current Purchase Price by the
number of one-thousandths of a Preferred Share for which a Right was
exercisable immediately prior to the first occurrence of a Section 13 Event
(or, if a Triggering Event has occurred prior to the first occurrence of a
Section 13 Event, multiplying the number of such one-thousandths of a Preferred
Share for which a Right was exercisable immediately prior to the first
occurrence of a Triggering Event by the Purchase Price in effect immediately
prior to such first occurrence) and (2) dividing that product (which, following
the first occurrence of a Section 13 Event, shall be referred to as the "Total
Exercise Price" for each Right and for all purposes of this Agreement) by 50%
of the current per share market price (determined pursuant to Section 11(d)
hereof) of the Common Shares of such Principal Party on the date of
consummation of such Section 13 Event;

                                  (B)      such Principal Party shall
thereafter be liable for, and shall assume, by virtue of such Section 13 Event,
all the obligations and duties of the Company pursuant to this Agreement;

                                  (C)      the term "Company" shall thereafter
be deemed to refer to such Principal Party, it being specifically intended that
the provisions of Section 11 hereof shall apply only to such Principal Party
following the first occurrence of a Section 13 Event;

                                  (D)      such Principal Party shall take such
steps (including, but not limited to, the reservation of a sufficient number of
its Common Shares) in connection with the consummation of any such transaction
as may be necessary to assure that the provisions hereof shall thereafter be
applicable, as nearly as reasonably may be, in relation to its Common Shares
thereafter deliverable upon the exercise of the Rights.

                 (b)      "Principal Party" shall mean, in the case of any
transaction described in clause (i), (ii) or (iii) of Section 13(a), the Person
or Acquiring Person referred to therein





                                      -22-
<PAGE>   26


(or such Person's or Acquiring Person's successor, including, if applicable,
the Company, if it is the surviving corporation), provided, however, that in
any such case, (i) if such Person is a direct or indirect Subsidiary of another
Person, "Principal Party" shall refer to such other Person and (ii) in case
such Person is a Subsidiary, directly or indirectly, of more than one Person,
"Principal Party" shall refer to whichever of such Persons is the issuer of the
Common Shares having the greatest aggregate value, and provided, further, that
for purposes of transactions described in clause (iii) hereof, "Principal
Party" shall refer to that Person receiving the greatest portion of the assets
or earning power transferred pursuant to such transaction or transactions.

                 (c)      If, for any reason, the Rights cannot be exercised
for Common Shares of such Principal Party as provided in Section 13(a), then
each holder of Rights shall have the right to exchange its Rights for cash from
such Principal Party in an amount equal to the number of Common Shares that it
would otherwise be entitled to purchase times 50% of the current per share
market price, as determined pursuant to Section 11(d) hereof, of such Common
Shares of such Principal Party.  If, for any reason, the foregoing formulation
cannot be applied to determine the cash amount into which the Rights are
exchangeable, then the Board of Directors, based upon the advice of one or more
nationally recognized investment banking firms, and based upon the total value
of the Company, shall determine such amount reasonably and with good faith to
the holders of Rights.  Any such determination shall be final and binding on
the Rights Agent.

                 (d)      Notwithstanding anything in this Agreement to the
contrary, Section 13 shall not be applicable to a transaction described in
clauses (i) and (ii) of Section 13(a) if: (i) such transaction is consummated
with a Person or Persons who acquired Common Shares pursuant to a Permitted
Offer (or a wholly-owned Subsidiary of any such Person or Persons); (ii) the
price per share of Common Shares offered in such transaction is not less than
the price per share of Common Shares paid to all holders of Common Shares whose
shares were purchased pursuant to such Permitted Offer; and (iii) the form of
consideration being offered to the remaining holders of Common Shares pursuant
to such transaction is the same form as the form of consideration paid pursuant
to such Permitted Offer.  Upon consummation of any such transaction
contemplated by this Section 13(d), all Rights hereunder shall expire.

                 (e)      The Company shall not consummate any Section 13 Event
unless the Principal Party shall have a sufficient number of authorized Common
Shares that have not been issued or reserved for issuance to permit the
exercise in full of the Rights in accordance with this Section 13 and unless
prior thereto the Company and such issuer shall have executed and delivered to
the Rights Agent a supplemental agreement confirming that such Principal Party
shall, upon consummation of such Section 13 Event, assume this Agreement in
accordance with Sections 13(a) and (b) hereof, that all rights of first refusal
or preemptive rights in respect of the issuance of Common Shares of such
Principal Party upon exercise of outstanding Rights have been waived, that
there are no rights, warrants, instruments or securities outstanding or any
agreements or arrangements which, as a result of the consummation of such
transaction, would eliminate or substantially diminish the benefits intended to
be afforded by the Rights and that such transaction shall not result in




                                      -23-

<PAGE>   27
a default by such Principal Party under this Agreement, and further providing
that, as soon as practicable after the date of such Section 13 Event, such
Principal Party will:

                          (i)     prepare and file a registration statement
under the Securities Act with respect to the Rights and the securities
purchasable upon exercise of the Rights on an appropriate form, use its best
efforts to cause such registration statement to become effective as soon as
practicable after such filing and use its best efforts to cause such
registration statement to remain effective (with a prospectus at all times
meeting the requirements of the Securities Act) until the Expiration Date, and
similarly comply with applicable state securities laws;

                          (ii)    use its best efforts to list (or continue the
listing of) the Rights and the securities purchasable upon exercise of the
Rights on a national securities exchange or to meet the eligibility
requirements for quotation on Nasdaq; and

                          (iii)   deliver to holders of the Rights historical
financial statements for such Principal Party which comply in all respects with
the requirements for registration on Form 10 (or any successor form) under the
Exchange Act.

                 In the event that at any time after the occurrence of a
Triggering Event some or all of the Rights shall not have been exercised at the
time of a transaction described in this Section 13, the Rights which have not
theretofore been exercised shall thereafter be exercisable in the manner
described in Section 13(a) (without taking into account any prior adjustment
required by Section 11(a)(ii)).

                 (f)      The provisions of this Section 13 shall similarly
apply to successive mergers or consolidations or sales or other transfers.

         SECTION 14.      FRACTIONAL RIGHTS AND FRACTIONAL SHARES.

                 (a)      The Company shall not be required to issue fractions
of Rights or to distribute Rights Certificates which evidence fractional
Rights.  In lieu of such fractional Rights, there shall be paid to the
registered holders of the Rights Certificates with regard to which such
fractional Rights would otherwise be issuable, an amount in cash equal to the
same fraction of the current market value of a whole Right.  For the purposes
of this Section 14(a), the current market value of a whole Right shall be the
closing price of the Rights for the Trading Day immediately prior to the date
on which such fractional Rights would have been otherwise issuable, as
determined pursuant to the second sentence of Section 11(d) hereof.

                 (b)      The Company shall not be required to issue fractions
of Preferred Shares (other than fractions that are integral multiples of one
one-thousandth of a Preferred Share) upon exercise of the Rights or to
distribute certificates which evidence fractional Preferred Shares (other than
fractions that are integral multiples of one one-thousandth of a Preferred
Share).  In lieu of fractional Preferred Shares that are not integral multiples
of one one-thousandth of a Preferred Share, the Company shall pay to the
registered holders




                                      -24-

<PAGE>   28
of Rights Certificates at the time such Rights are exercised as herein provided
an amount in cash equal to the same fraction of the current market value of a
Common Share.  For purposes of this Section 14(b), the current market value of
a Common Share shall be the closing price of a Common Share (as determined
pursuant to the second sentence of Section 11(d) hereof) for the Trading Day
immediately prior to the date of such exercise.

                 (c)      The holder of a Right by the acceptance of the Right
expressly waives his or her right to receive any fractional Rights or any
fractional shares upon exercise of a Right.

         SECTION 15.      RIGHTS OF ACTION.  All rights of action in respect of
this Agreement, excepting the rights of action given to the Rights Agent under
Section 18 hereof, are vested in the respective registered holders of the
Rights Certificates (and, prior to the Distribution Date, the registered
holders of the Common Shares); and any registered holder of any Rights
Certificate (or, prior to the Distribution Date, of the Common Shares), without
the consent of the Rights Agent or of the holder of any other Rights
Certificate (or, prior to the Distribution Date, of the Common Shares), may, in
his or her own behalf and for his or her own benefit, enforce, and may
institute and maintain any suit, action or proceeding against the Company to
enforce, or otherwise act in respect of, his or her right to exercise the
Rights evidenced by such Rights Certificate in the manner provided in such
Rights Certificate and in this Agreement.  Without limiting the foregoing or
any remedies available to the holders of Rights, it is specifically
acknowledged that the holders of Rights would not have an adequate remedy at
law for any breach of this Agreement and will be entitled to specific
performance of the obligations under, and injunctive relief against actual or
threatened violations of, the obligations of any Person subject to this
Agreement.

         SECTION 16.      AGREEMENT OF RIGHTS HOLDERS.  Every holder of a
Right, by accepting the same, consents and agrees with the Company and the
Rights Agent and with every other holder of a Right that:

                 (a)      prior to the Distribution Date, the Rights will be
transferable only in connection with the transfer of the Common Shares;

                 (b)      after the Distribution Date, the Rights Certificates
are transferable only on the registry books of the Rights Agent if surrendered
at the principal office or offices of the Rights Agent designated for such
purposes, duly endorsed or accompanied by a proper instrument of transfer and
with the appropriate forms and certificates fully executed; and

                 (c)      subject to Sections 6(a) and 7(f) hereof, the Company
and the Rights Agent may deem and treat the person in whose name the Rights
Certificate (or, prior to the Distribution Date, the associated Common Shares
certificate) is registered as the absolute owner thereof and of the Rights
evidenced thereby (notwithstanding any notations of ownership or writing on the
Rights Certificates or the associated Common Shares certificate made by anyone
other than the Company or the Rights Agent) for all purposes whatsoever, and
neither the Company nor the Rights Agent shall be affected by any notice to the
contrary.




                                      -25-
<PAGE>   29
         SECTION 17.      RIGHTS CERTIFICATE HOLDER NOT DEEMED A STOCKHOLDER.
No holder, as such, of any Rights Certificate shall be entitled to vote,
receive dividends or be deemed for any purpose the holder of the Preferred
Shares or any other securities of the Company which may at any time be issuable
on the exercise of the Rights represented thereby, nor shall anything contained
herein or in any Rights Certificate be construed to confer upon the holder of
any Rights Certificate, as such, any of the rights of a stockholder of the
Company or any right to vote for the election of directors or upon any matter
submitted to stockholders at any meeting thereof, or to give or withhold
consent to any corporate action, or to receive notice of meetings or other
actions affecting stockholders (except as provided in Section 25 hereof), or to
receive dividends or subscription rights, or otherwise, until the Right or
Rights evidenced by such Rights Certificate shall have been exercised in
accordance with the provisions hereof.

         SECTION 18.      CONCERNING THE RIGHTS AGENT.

                 (a)      The Company agrees to pay to the Rights Agent
reasonable compensation for all services rendered by it hereunder and, from
time to time, on demand of the Rights Agent, its reasonable expenses and
counsel fees and other disbursements incurred in the administration and
execution of this Agreement and the exercise and performance of its duties
hereunder.  The Company also agrees to indemnify the Rights Agent for, and to
hold it harmless against, any loss, liability or expense, incurred without
negligence, bad faith or willful misconduct on the part of the Rights Agent,
for anything done or omitted by the Rights Agent in connection with the
acceptance and administration of this Agreement, including the costs and
expenses of defending against any claim of liability in the premises.  Anything
in this Agreement to the contrary notwithstanding, in no event shall the Rights
Agent be liable for special, indirect or consequential loss or damage of any
kind whatsoever (including but not limited to lost profits), even if the Rights
Agent has been advised of the likelihood of such loss or damage and regardless
of the form of the action.

                 (b)      The Rights Agent shall be protected and shall incur
no liability for, or in respect of any action taken, suffered or omitted by it
in connection with, its administration of this Agreement in reliance upon any
Rights Certificate or certificate for the Preferred Shares or Common Shares or
for other securities of the Company, instrument of assignment or transfer,
power of attorney, endorsement, affidavit, letter, notice, direction, consent,
certificate, statement or other paper or document believed by it to be genuine
and to be signed, executed and, where necessary, verified or acknowledged, by
the proper Person or Persons, or otherwise upon the advice of counsel as set
forth in Section 20 hereof.

         SECTION 19.      MERGER OR CONSOLIDATION OR CHANGE OF NAME OF RIGHTS
AGENT.

                 (a)      Any corporation into which the Rights Agent or any
successor Rights Agent may be merged or with which it may be consolidated, or
any corporation resulting from any merger or consolidation to which the Rights
Agent or any successor Rights Agent shall be a party, or any corporation
succeeding to the corporate trust business of the Rights Agent or any successor
Rights Agent, shall be the successor to the Rights Agent under this




                                      -26-
<PAGE>   30
Agreement without the execution or filing of any paper or any further act on
the part of any of the parties hereto; provided, however, that such corporation
would be eligible for appointment as a successor Rights Agent under the
provisions of Section 21 hereof.  In case at the time such successor Rights
Agent shall succeed to the agency created by this Agreement, any of the Rights
Certificates shall have been countersigned but not delivered, any such
successor Rights Agent may adopt the countersignature of the predecessor Rights
Agent and deliver such Rights Certificates so countersigned; and in case at
that time any of the Rights Certificates shall not have been countersigned, any
successor Rights Agent may countersign such Rights Certificates either in the
name of the predecessor Rights Agent or in the name of the successor Rights
Agent; and in all such cases such Rights Certificates shall have the full force
provided in the Rights Certificates and in this Agreement.

                 (b)      In case at any time the name of the Rights Agent
shall be changed and at such time any of the Rights Certificates shall have
been countersigned but not delivered, the Rights Agent may adopt the
countersignature under its prior name and deliver Rights Certificates so
countersigned; and in case at that time any of the Rights Certificates shall
not have been countersigned, the Rights Agent may countersign such Rights
Certificates either in its prior name or in its changed name; and in all such
cases such Rights Certificates shall have the full force provided in the Rights
Certificates and in this Agreement.

         SECTION 20.      DUTIES OF RIGHTS AGENT.  The Rights Agent undertakes
the duties and obligations imposed by this Agreement upon the following terms
and conditions, by all of which the Company and the holders of Rights
Certificates, by their acceptance thereof, shall be bound:

                 (a)      The Rights Agent may consult with legal counsel (who
may be legal counsel for the Company), and the opinion of such counsel shall be
full and complete authorization and protection to the Rights Agent as to any
action taken or omitted by it in good faith and in accordance with such
opinion.

                 (b)      Whenever in the performance of its duties under this
Agreement the Rights Agent shall deem it necessary or desirable that any fact
or matter (including, without limitation, the identity of any Acquiring Person
and the determination of "current per share market price") be proved or
established by the Company prior to taking or suffering any action hereunder,
such fact or matter (unless other evidence in respect thereof be herein
specifically prescribed) may be deemed to be conclusively proved and
established by a certificate signed by any one of the Chairman of the Board,
the Chief Executive Officer, the President, any Vice President, the Chief
Financial Officer, the Secretary or any Assistant Secretary of the Company and
delivered to the Rights Agent; and such certificate shall be full authorization
to the Rights Agent for any action taken or suffered in good faith by it under
the provisions of this Agreement in reliance upon such certificate.

                 (c)      The Rights Agent shall be liable hereunder to the
Company and any other Person only for its own negligence, bad faith or willful
misconduct.




                                      -27-
<PAGE>   31
                 (d)      The Rights Agent shall not be liable for or by reason
of any of the statements of fact or recitals contained in this Agreement or in
the Rights Certificates (except its countersignature thereof) or be required to
verify the same, but all such statements and recitals are and shall be deemed
to have been made by the Company only.

                 (e)      The Rights Agent shall not be under any
responsibility in respect of the validity of this Agreement or the execution
and delivery hereof (except the due execution hereof by the Rights Agent) or in
respect of the validity or execution of any Rights Certificate (except its
countersignature thereof); nor shall it be responsible for any breach by the
Company of any covenant or condition contained in this Agreement or in any
Rights Certificate; nor shall it be responsible for any change in the
exercisability of the Rights or any adjustment in the terms of the Rights
(including the manner, method or amount thereof) provided for in Sections 3,
11, 13, 23 or 24, or the ascertaining of the existence of facts that would
require any such change or adjustment (except with respect to the exercise of
Rights evidenced by Rights Certificates after receipt by the Rights Agent of a
certificate furnished pursuant to Section 12 describing such change or
adjustment); nor shall it by any act hereunder be deemed to make any
representation or warranty as to the authorization or reservation of any
Preferred Shares to be issued pursuant to this Agreement or any Rights
Certificate or as to whether any Preferred Shares will, when issued, be validly
authorized and issued, fully paid and nonassessable.

                 (f)      The Company agrees that it will perform, execute,
acknowledge and deliver or cause to be performed, executed, acknowledged and
delivered all such further and other acts, instruments and assurances as may
reasonably be required by the Rights Agent for the carrying out or performing
by the Rights Agent of the provisions of this Agreement.

                 (g)      The Rights Agent is hereby authorized and directed to
accept instructions with respect to the performance of its duties hereunder
from any one of the Chairman of the Board, the Chief Executive Officer, the
President, any Vice President, the Chief Financial Officer, the Secretary or
any Assistant Secretary of the Company, and to apply to such officers for
advice or instructions in connection with its duties, and it shall not be
liable for any action taken or suffered by it in good faith in accordance with
instructions of any such officer or for any delay in acting while waiting for
those instructions.  Any application by the Rights Agent for written
instructions from the Company may, at the option of the Rights Agent, set forth
in writing any action proposed to be taken or omitted by the Rights Agent under
this Rights Agreement and the date on and/or after which such action shall be
taken or such omission shall be effective.  The Rights Agent shall not be
liable for any action taken by, or omission of, the Rights Agent in accordance
with a proposal included in any such application on or after the date specified
in such application (which date shall not be less than five (5) Business Days
after the date any officer of the Company actually receives such application,
unless any such officer shall have consented in writing to an earlier date)
unless, prior to taking any such action (or the effective date in the case of
an omission), the Rights Agent shall have received written instructions in
response to such application specifying the action to be taken or omitted.

                 (h)      The Rights Agent and any stockholder, director,
officer or employee




                                      -28-
<PAGE>   32
of the Rights Agent may buy, sell or deal in any of the Rights or other
securities of the Company or become pecuniarily interested in any transaction
in which the Company may be interested, or contract with or lend money to the
Company or otherwise act as fully and freely as though it were not Rights Agent
under this Agreement.  Nothing herein shall preclude the Rights Agent from
acting in any other capacity for the Company or for any other legal entity.

                 (i)      The Rights Agent may execute and exercise any of the
rights or powers hereby vested in it or perform any duty hereunder either
itself or by or through its attorneys or agents, and the Rights Agent shall not
be answerable or accountable for any act, default, neglect or misconduct of any
such attorneys or agents or for any loss to the Company resulting from any such
act, default, neglect or misconduct, provided reasonable care was exercised in
the selection and continued employment thereof.

                 (j)      No provision of this Agreement shall require the
Rights Agent to expend or risk its own funds or otherwise incur any financial
liability in the performance of any of its duties hereunder or in the exercise
of its rights if there shall be reasonable grounds for believing that repayment
of such funds or adequate indemnification against such risk or liability is not
reasonably assured to it.

                 (k)      If, with respect to any Rights Certificate
surrendered to the Rights Agent for exercise or transfer, the certificate
attached to the form of assignment or form of election to purchase, as the case
may be, has either not been completed or indicates an affirmative response to
clause 1 and/or 2 thereof, the Rights Agent shall not take any further action
with respect to such requested exercise or transfer without first consulting
with the Company.

         SECTION 21.      CHANGE OF RIGHTS AGENT.  The Rights Agent or any
successor Rights Agent may resign and be discharged from its duties under this
Agreement upon thirty (30) days' notice in writing mailed to the Company and to
each transfer agent of the Preferred Shares and the Common Shares by registered
or certified mail, and to the holders of the Rights Certificates by first-class
mail.  The Company may remove the Rights Agent or any successor Rights Agent
upon thirty (30) days' notice in writing, mailed to the Rights Agent or
successor Rights Agent, as the case may be, and to each transfer agent of the
Preferred Shares and the Common Shares by registered or certified mail, and to
the holders of the Rights Certificates by first-class mail.  If the Rights
Agent shall resign or be removed or shall otherwise become incapable of acting,
the Company shall appoint a successor to the Rights Agent.  If the Company
shall fail to make such appointment within a period of thirty (30) days after
giving notice of such removal or after it has been notified in writing of such
resignation or incapacity by the resigning or incapacitated Rights Agent or by
the holder of a Rights Certificate (who shall, with such notice, submit his or
her Rights Certificate for inspection by the Company), then the registered
holder of any Rights Certificate may apply to any court of competent
jurisdiction for the appointment of a new Rights Agent.  Any successor Rights
Agent, whether appointed by the Company or by such a court, shall be a
corporation organized and doing business under the laws of the United States or
of any state of the United States, in good standing, which is authorized
under such laws to exercise 




                                      -29-
<PAGE>   33
corporate trust or stockholder services powers and is subject to supervision or
examination by federal or state authority and which has at the time of its 
appointment as Rights Agent a combined capital and surplus of at least 
$50 million.  After appointment, the successor Rights Agent shall be vested 
with the same powers, rights, duties and responsibilities as if it had been 
originally named as Rights Agent without further act or deed; but the 
predecessor Rights Agent shall deliver and transfer to the successor Rights 
Agent any property at the time held by it hereunder, and execute and deliver any
further assurance, conveyance, act or deed necessary for the purpose.  Not later
than the effective date of any such appointment, the Company shall file notice 
thereof in writing with the predecessor Rights Agent and each transfer agent of 
the Preferred Shares and the Common Shares, and mail a notice thereof in writing
to the registered holders of the Rights Certificates.  Failure to give any 
notice provided for in this Section 21, however, or any defect therein, shall 
not affect the legality or validity of the resignation or removal of the Rights
Agent or the appointment of the successor Rights Agent, as the case may be.

         SECTION 22.      ISSUANCE OF NEW RIGHTS CERTIFICATES.  Notwithstanding
any of the provisions of this Agreement or of the Rights to the contrary, the
Company may, at its option, issue new Rights Certificates evidencing Rights in
such form as may be approved by its Board of Directors to reflect any
adjustment or change in the Purchase Price and the number or kind or class of
shares or other securities or property purchasable under the Rights
Certificates made in accordance with the provisions of this Agreement.  In
addition, in connection with the issuance or sale of Common Shares following
the Distribution Date and prior to the redemption or expiration of the Rights,
the Company (a) shall, with respect to Common Shares so issued or sold pursuant
to the exercise of stock options or under any employee plan or arrangement or
upon the exercise, conversion or exchange of the American Home Products
Unsecured Convertible Promissory Notes or the Glycomed convertible subordinated
debentures outstanding at the date hereof or upon the exercise, conversion or
exchange of securities hereinafter issued by the Company and (b) may, in any
other case, if deemed necessary or appropriate by the Board of Directors of the
Company, issue Rights Certificates representing the appropriate number of
Rights in connection with such issuance or sale; provided, however, that (i) no
such Rights Certificate shall be issued and this sentence shall be null and
void ab initio if, and to the extent that, such issuance or this sentence would
create a significant risk of or result in material adverse tax consequences to
the Company or the Person to whom such Rights Certificate would be issued or
would create a significant risk of or result in such options' or employee
plans' or arrangements' failing to qualify for otherwise available special tax
treatment and (ii) no such Rights Certificate shall be issued if, and to the
extent that, appropriate adjustment shall otherwise have been made in lieu of
the issuance thereof.

         SECTION 23.      REDEMPTION.

                 (a)      The Company may, at its option and with the approval
of the Board of Directors, at any time prior to the Close of Business on the
earlier of (i) the tenth day following the Shares Acquisition Date or such
later date as may be determined by action of a majority of Continuing Directors
then in office and publicly announced by the Company or (ii) the Final
Expiration Date, redeem all but not less than all the then outstanding




                                      -30-
<PAGE>   34
Rights at a redemption price of $0.01 per Right, appropriately adjusted to
reflect any stock split, stock dividend or similar transaction occurring after
the date hereof (such redemption price being herein referred to as the
"Redemption Price") and the Company may, at its option, pay the Redemption
Price either in Common Shares (based on the current per share market price
thereof (as determined pursuant to Section 11(d) hereof) at the time of
redemption) or cash.  Such redemption of the Rights by the Company may be made
effective at such time, on such basis and with such conditions as the Board of
Directors in its sole discretion may establish; provided, however, if the Board
of Directors of the Company authorizes redemption of the Rights on or after the
time a Person becomes an Acquiring Person, then there must be Continuing
Directors then in office and such authorization shall require the concurrence
of a majority of such Continuing Directors.

                 (b)      Immediately upon the action of the Board of Directors
of the Company ordering the redemption of the Rights, evidence of which shall
have been filed with the Rights Agent, and without any further action and
without any notice, the right to exercise the Rights will terminate and the
only right thereafter of the holders of Rights shall be to receive the
Redemption Price.  The Company shall promptly give public notice of any such
redemption; provided, however, that the failure to give or any defect in, any
such notice shall not effect the validity of such redemption.  Within ten (10)
days after the action of the Board of Directors ordering the redemption of the
Rights, the Company shall give notice of such redemption to the Rights Agent
and the holders of the then outstanding Rights by mailing such notice to all
such holders at their last addresses as they appear upon the registry books of
the Rights Agent or, prior to the Distribution Date, on the registry books of
the transfer agent for the Common Shares.  Any notice which is mailed in the
manner herein provided shall be deemed given, whether or not the holder
receives the notice.  Each such notice of redemption will state the method by
which the payment of the Redemption Price will be made.  Neither the Company
nor any of its Affiliates or Associates may redeem, acquire or purchase for
value any Rights at any time in any manner other than that specifically set
forth in this Section 23 or in Section 24 hereof, and other than in connection
with the purchase of Common Shares prior to the Distribution Date.

         SECTION 24.      EXCHANGE.

                 (a)      Subject to applicable laws, rules and regulations,
and subject to subsection (c) below, the Company may, at its option, by
majority vote of the Board of Directors and a majority vote of the Continuing
Directors, at any time after the occurrence of a Triggering Event, exchange all
or part of the then outstanding and exercisable Rights (which shall not include
Rights that have become void pursuant to the provisions of Section 7(e) hereof)
for Common Shares at an exchange ratio of one Common Share per Right,
appropriately adjusted to reflect any stock split, stock dividend or similar
transaction occurring after the date hereof (such exchange ratio being
hereinafter referred to as the "Ratio of Exchange").  Notwithstanding the
foregoing, the Board of Directors shall not be empowered to effect such
exchange at any time after any Person (other than the Company, any Subsidiary
of the Company, any employee benefit plan of the Company or any such
Subsidiary, or any entity holding Common Shares for or pursuant to the terms of
any such plan), together with all Affiliates and Associates of such Person,
becomes the Beneficial




                                      -31-

<PAGE>   35
Owner of 50% or more of the Common Shares then outstanding.

                 (b)      Immediately upon the action of the Board of Directors
ordering the exchange of any Rights pursuant to subsection (a) of this Section
24 and without any further action and without any notice, the right to exercise
such Rights shall terminate and the only right thereafter of a holder of such
Rights shall be to receive that number of Common Shares equal to the number of
such Rights held by such holder multiplied by the Ratio of Exchange.  The
Company shall give public notice of any such exchange; provided, however, that
the failure to give, or any defect in, such notice shall not affect the
validity of such exchange.  The Company shall mail a notice of any such
exchange to all of the holders of such Rights at their last addresses as they
appear upon the registry books of the Rights Agent.  Any notice which is mailed
in the manner herein provided shall be deemed given, whether or not the holder
receives the notice.  Each such notice of exchange will state the method by
which the exchange of the Common Shares for Rights will be effected and, in the
event of any partial exchange, the number of Rights which will be exchanged.
Any partial exchange shall be effected pro rata based on the number of Rights
(other than Rights which have become void pursuant to the provisions of Section
7(e) hereof) held by each holder of Rights.

                 (c)      In the event that there shall not be sufficient
Common Shares issued but not outstanding or authorized but unissued to permit
any exchange of Rights as contemplated in accordance with Section 24(a), the
Company shall either take such action as may be necessary to authorize
additional Common Shares for issuance upon exchange of the Rights or
alternatively, at the option of a majority of the Board of Directors, with
respect to each Right (i) pay cash in an amount equal to the Current Value (as
hereinafter defined), in lieu of issuing Common Shares in exchange therefor, or
(ii) issue debt or equity securities or a combination thereof, having a value
equal to the Current Value, in lieu of issuing Common Shares in exchange for
each such Right, where the value of such securities shall be determined by a
nationally recognized investment banking firm selected by the Board of
Directors by majority vote of the Board of Directors, or (iii) deliver any
combination of cash, property, Common Shares and/or other securities having a
value equal to the Current Value in exchange for each Right.  For purposes of
this Section 24(c) only, the Current Value shall mean the product of the
current per share market price of Common Shares (determined pursuant to Section
11(d) on the date of the occurrence of the event described above in
subparagraph (a)) multiplied by the number of Common Shares for which the Right
otherwise would be exchangeable if there were sufficient shares available.  To
the extent that the Company determines that some action need be taken pursuant
to clauses (i), (ii) or (iii) of this Section 24(c), the Board of Directors may
temporarily suspend the exercisability of the Rights for a period of up to
sixty (60) days following the date on which the event described in Section
24(a) shall have occurred, in order to seek any authorization of additional
Common Shares and/or to decide the appropriate form of distribution to be made
pursuant to the above provision and to determine the value thereof.  In the
event of any such suspension, the Company shall issue a public announcement
stating that the exercisability of the Rights has been temporarily suspended.

                 (d)      The Company shall not be required to issue fractions
of Common




                                      -32-
<PAGE>   36
Shares or to distribute certificates which evidence fractional Common Shares.
In lieu of such fractional Common Shares, there shall be paid to the registered
holders of the Rights Certificates with regard to which such fractional Common
Shares would otherwise be issuable, an amount in cash equal to the same
fraction of the current per share market value of a whole Common Share (as
determined pursuant to the second sentence of Section 11(d) hereof).

                 (e)      The Company may, at its option, by majority vote of
the Board of Directors, at any time before any Person has become an Acquiring
Person, exchange all or part of the then outstanding Rights for rights of
substantially equivalent value, as determined reasonably and with good faith by
the Board of Directors, based upon the advice of one or more nationally
recognized investment banking firms.

                 (f)      Immediately upon the action of the Board of Directors
ordering the exchange of any Rights pursuant to subsection (e) of this Section
24 and without any further action and without any notice, the right to exercise
such Rights shall terminate and the only right thereafter of a holder of such
Rights shall be to receive that number of rights in exchange therefor as has
been determined by the Board of Directors in accordance with subsection (e)
above.  The Company shall give public notice of any such exchange; provided,
however, that the failure to give, or any defect in, such notice shall not
affect the validity of such exchange.  The Company shall mail a notice of any
such exchange to all of the holders of such Rights at their last addresses as
they appear upon the registry books of the transfer agent for the Common Shares
of the Company.  Any notice which is mailed in the manner herein provided shall
be deemed given, whether or not the holder receives the notice.  Each such
notice of exchange will state the method by which the exchange of the Rights
will be effected.

         SECTION 25.      NOTICE OF CERTAIN EVENTS.

                 (a)      In case the Company shall propose to effect or permit
to occur any Triggering Event described in Section 11(a)(ii)(A) or 11(a)(ii)(B)
or a Section 13 Event, the Company shall give notice thereof to each holder of
Rights in accordance with Section 26 hereof at least twenty (20) days prior to
occurrence of such Triggering Event or such Section 13 Event.

                 (b)      In case any Triggering Event or Section 13 Event
shall occur, then, in any such case, the Company shall as soon as practicable
thereafter give to each holder of a Rights Certificate, in accordance with
Section 26 hereof, a notice of the occurrence of such event, which shall
specify the event and the consequences of the event to holders of Rights under
Sections 11(a)(ii) and 13 hereof.

         SECTION 26.      NOTICES.  Notices or demands authorized by this
Agreement to be given or made by the Rights Agent or by the holder of any
Rights Certificate to or on the Company shall be sufficiently given or made if
sent by first-class mail, postage prepaid, addressed (until another address is
filed in writing with the Rights Agent) as follows:




                                      -33-

<PAGE>   37
                                  LIGAND PHARMACEUTICALS INCORPORATED
                                  9393 Towne Centre Drive
                                  San Diego, CA 92121
                                  Attn:  President

         Subject to the provisions of Section 21 hereof, any notice or demand
authorized by this Agreement to be given or made by the Company or by the
holder of any Rights Certificate to or on the Rights Agent shall be
sufficiently given or made if sent by first-class mail, postage prepaid,
addressed (until another address is filed in writing with the Company) as
follows:

                                  WELLS FARGO BANK N.A.
                                  707 Wilshire Boulevard, W11-2
                                  Los Angeles, CA 90017
                                  Attention:  Stock Transfer Administration


Notices or demands authorized by this Agreement to be given or made by the
Company or the Rights Agent to the holder of any Rights Certificate shall be
sufficiently given or made if sent by first-class mail, postage prepaid,
addressed to such holder at the address of such holder as shown on the registry
books of the Company.

         SECTION 27.      SUPPLEMENTS AND AMENDMENTS.  Prior to the
Distribution Date, the Company may supplement or amend this Agreement in any
respect without the approval of any holders of Rights and the Rights Agent
shall, if the Company so directs, execute such supplement or amendment.  From
and after the Distribution Date, the Company and the Rights Agent may from time
to time supplement or amend this Agreement without the approval of any holders
of Rights in order to (i) cure any ambiguity, (ii) correct or supplement any
provision contained herein which may be defective or inconsistent with any
other provisions herein, (iii) shorten or lengthen any time period hereunder
(which lengthening or shortening, following the first occurrence of an event
set forth in the proviso to Section 23(a) hereof, shall be effective only if
there are Continuing Directors and shall require the concurrence of a majority
of such Continuing Directors) or (iv) to change or supplement the provisions
hereunder in any manner that the Company may deem necessary or desirable and
that shall not adversely affect the interests of the holders of Rights (other
than an Acquiring Person or an Affiliate or Associate of an Acquiring Person);
provided, this Agreement may not be supplemented or amended to lengthen,
pursuant to clause (iii) of this sentence, (A) a time period relating to when
the Rights may be redeemed at such time as the Rights are not then redeemable
or (B) any other time period unless such lengthening is for the purpose of
protecting, enhancing or clarifying the rights of, and/or the benefits to, the
holders of Rights.  Upon the delivery of a certificate from an appropriate
officer of the Company that states that the proposed supplement or amendment is
in compliance with the terms of this Section 27, the Rights Agent shall execute
such supplement or amendment.  Prior to the Distribution Date, the interests of
the holders of Rights shall be deemed coincident with the interests of the
holders of Common Shares.




                                      -34-

<PAGE>   38
         SECTION 28.      SUCCESSORS.  All the covenants and provisions of this
Agreement by or for the benefit of the Company or the Rights Agent shall bind
and inure to the benefit of their respective successors and assigns hereunder.

         SECTION 29.      DETERMINATIONS AND ACTIONS BY THE BOARD OF DIRECTORS,
ETC.  For all purposes of this Agreement, any calculation of the number of
Common Shares outstanding at any particular time, including for purposes of
determining the particular percentage of such outstanding Common Shares of
which any Person is the Beneficial Owner, shall be made in accordance with the
last sentence of Rule 13d-3(d)(1)(i) of the General Rules and Regulations under
the Exchange Act.  The Board of Directors of the Company (and, where
specifically provided for herein, the Continuing Directors) shall have the
exclusive power and authority to administer this Agreement and to exercise all
rights and powers specifically granted to the Board, or the Company (or, where
specifically provided for herein, the Continuing Directors), or as may be
necessary or advisable in the administration of this Agreement, including,
without limitation, the right and power to (i) interpret the provisions of this
Agreement and (ii) make all determinations deemed necessary or advisable for
the administration of this Agreement (including a determination to redeem or
not redeem the Rights or to amend the Agreement).  All such actions,
calculations, interpretations and determinations (including, for purposes of
clause (y) below, all omissions with respect to the foregoing) which are done
or made by the Board (or, where specifically provided for herein, by the
Continuing Directors) in good faith, shall (x) be final, conclusive and binding
on the Company, the Rights Agent, the holders of the Rights Certificates and
all other parties and (y) not subject the Board or the Continuing Directors to
any liability to the holders of the Rights.

         SECTION 30.      BENEFITS OF THIS AGREEMENT.   Nothing in this
Agreement shall be construed to give to any Person other than the Company, the
Rights Agent and the registered holders of the Rights Certificates (and, prior
to the Distribution Date, the Common Shares) any legal or equitable right,
remedy or claim under this Agreement; but this Agreement shall be for the sole
and exclusive benefit of the Company, the Rights Agent and the registered
holders of the Rights Certificates (and, prior to the Distribution Date, the
Common Shares).

         SECTION 31.      SEVERABILITY.   If any term, provision, covenant or
restriction of this Agreement is held by a court of competent jurisdiction or
other authority to be invalid, void or unenforceable, the remainder of the
terms, provisions, covenants and restrictions of this Agreement shall remain in
full force and effect and shall in no way be affected, impaired or invalidated;
provided, however, that notwithstanding anything in this Agreement to the
contrary, if any such term, provision, covenant or restriction is held by such
court or authority to be invalid, void or unenforceable and the Board of
Directors of the Company determines in its good faith judgment that severing
the invalid language from this Agreement would adversely affect the purpose or
effect of this Agreement, the right of redemption set forth in Section 23
hereof shall be reinstated and shall not expire until the close of business on
the tenth day following the date of such determination by the Board of
Directors.




                                      -35-

<PAGE>   39
         SECTION 32.      GOVERNING LAW.  This Agreement and each Right and
each Rights Certificate issued hereunder shall be deemed to be a contract made
under the laws of the State of Delaware and for all purposes shall be governed
by and construed in accordance with the laws of such State applicable to
contracts to be made and performed entirely within such State.

         SECTION 33.      COUNTERPARTS.  This Agreement may be executed in any
number of counterparts and each of such counterparts shall for all purposes be
deemed to be an original, and all such counterparts shall together constitute
but one and the same instrument.

         SECTION 34.      DESCRIPTIVE HEADINGS.  Descriptive headings of the
several Sections of this Agreement are inserted for convenience only and shall
not control or affect the meaning or construction of any of the provisions
hereof.

               [Remainder of This Page Intentionally Left Blank]




                                      -36-

<PAGE>   40
         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed as of the day and year first above written.


"COMPANY"                         LIGAND PHARMACEUTICALS INCORPORATED


                                        By:  /s/ DAVID E. ROBINSON 
                                           -----------------------------------
                                           Name:  David E. Robinson 
                                           Title:  Chairman, President and CEO

"RIGHTS AGENT"                             WELLS FARGO BANK N.A.


                                        By:  /s/ ROSA M. BAUTISTA
                                           -----------------------------------  
                                           Name:  Rosa M. Bautista 
                                           Title: Assistant Vice President





                                      -37-

<PAGE>   41
                                   EXHIBIT A

               CERTIFICATE OF DESIGNATION OF RIGHTS, PREFERENCES
                               AND PRIVILEGES OF

                     SERIES A PARTICIPATING PREFERRED STOCK
                     OF LIGAND PHARMACEUTICALS INCORPORATED


         The undersigned, David E. Robinson and William L. Respess, do hereby
certify:

         1.      That they are the duly elected and acting President and
Secretary, respectively, of Ligand Pharmaceuticals Incorporated, a Delaware
corporation (the "Corporation").

         2.      That pursuant to the authority conferred upon the Board of
Directors by the Amended and Restated Certificate of Incorporation of the said
Corporation, the said Board of Directors adopted the following resolution
creating a series of 80,000 shares of Preferred Stock designated as Series A
Participating Preferred Stock:

         "RESOLVED, that pursuant to the authority vested in the Board of
         Directors of the corporation by the Amended and Restated Certificate
         of Incorporation, the Board of Directors does hereby provide for the
         issue of a series of Preferred Stock, par value $.001 per share, of
         the Corporation, to be designated "Series A Participating Preferred
         Stock," initially consisting of 80,000 shares and to the extent that
         the designations, powers, preferences and relative and other special
         rights and the qualifications, limitations and restrictions of the
         Series A Participating Preferred Stock are not stated and expressed in
         the Amended and Restated Certificate of Incorporation, does hereby fix
         and herein state and express such designations, powers, preferences
         and relative and other special rights and the qualifications,
         limitations and restrictions thereof, as follows (all terms used
         herein which are defined in the Amended and Restated Certificate of
         Incorporation shall be deemed to have the meanings provided therein):

         SECTION 1.       DESIGNATION AND AMOUNT.  The shares of such series
shall be designated as "Series A Participating Preferred Stock," par value
$.001 per share, and the number of shares constituting such series shall be
80,000.

         SECTION 2.       DIVIDENDS AND DISTRIBUTIONS.

                 (A)      Subject to the prior and superior right of the
holders of any shares of any series of Preferred Stock ranking prior and
superior to the shares of Series A Participating Preferred Stock with respect
to dividends, the holders of shares of Series A Participating Preferred Stock
shall be entitled to receive when, as and if declared by the Board of Directors
out of funds legally available for the purpose, quarterly dividends payable in
cash on the last day of September, December, March and June in each year





                                      A-1
<PAGE>   42
(each such date being referred to herein as a "Quarterly Dividend Payment
Date"), commencing on the first Quarterly Dividend Payment Date after the first
issuance of a share or fraction of a share of Series A Participating Preferred
Stock, in an amount per share (rounded to the nearest cent) equal to, subject
to the provision for adjustment hereinafter set forth, 1,000 times the
aggregate per share amount of all cash dividends, and 1,000 times the aggregate
per share amount (payable in kind) of all non-cash dividends or other
distributions other than a dividend payable in shares of Common Stock or a
subdivision of the outstanding shares of Common Stock (by reclassification or
otherwise), declared on the Common Stock of the Corporation (the "Common
Stock") since the immediately preceding Quarterly Dividend Payment Date, or,
with respect to the first Quarterly Dividend Payment Date, since the first
issuance of any share or fraction of a share of Series A Participating
Preferred Stock.  In the event the Corporation shall at any time after
September 13, 1996 (the "Rights Declaration Date") (i) declare any dividend on
Common Stock payable in shares of Common Stock, (ii) subdivide the outstanding
Common Stock, or (iii) combine the outstanding Common Stock into a smaller
number of shares, then in each such case the amount to which holders of shares
of Series A Participating Preferred Stock were entitled immediately prior to
such event under the preceding sentence shall be adjusted by multiplying such
amount by a fraction, the numerator of which is the number of shares of Common
Stock outstanding immediately after such event and the denominator of which is
the number of shares of Common Stock that were outstanding immediately prior to
such event.

                 (B)      The Corporation shall declare a dividend or
distribution on the Series A Participating Preferred Stock as provided in
paragraph (A) above immediately after it declares a dividend or distribution on
the Common Stock (other than a dividend payable in shares of Common Stock).

                 (C)      Dividends shall begin to accrue and be cumulative on
outstanding shares of Series A Participating Preferred Stock from the Quarterly
Dividend Payment Date next preceding the date of issue of such shares of Series
A Participating Preferred Stock, unless the date of issue of such shares is
prior to the record date for the first Quarterly Dividend Payment Date, in
which case dividends on such shares shall begin to accrue from the date of
issue of such shares, or unless the date of issue is a Quarterly Dividend
Payment Date or is a date after the record date for the determination of
holders of shares of Series A Participating Preferred Stock entitled to receive
a quarterly dividend and before such Quarterly Dividend Payment Date, in either
of which events such dividends shall begin to accrue and be cumulative from
such Quarterly Dividend Payment Date.  Accrued but unpaid dividends shall not
bear interest.  Dividends paid on the shares of Series A Participating
Preferred Stock in an amount less than the total amount of such dividends at
the time accrued and payable on such shares shall be allocated pro rata on a
share-by-share basis among all such shares at the time outstanding.  The Board
of Directors may fix a record date for the determination of holders of shares
of Series A Participating Preferred Stock entitled to receive payment of a
dividend or distribution declared thereon, which record date shall be no more
than 30 days prior to the date fixed for the payment thereof.

SECTION 3.       VOTING RIGHTS.   The holders of shares of Series A
Participating





                                      A-2
<PAGE>   43
Preferred Stock shall have the following voting rights:

                 (A)      Subject to the provision for adjustment hereinafter
set forth, each share of Series A Participating Preferred Stock shall entitle
the holder thereof to 1,000 votes on all matters submitted to a vote of the
stockholders of the Corporation.  In the event the Corporation shall at any
time after the Rights Declaration Date (i) declare any dividend on Common Stock
payable in shares of Common Stock, (ii) subdivide the outstanding Common Stock,
or (iii) combine the outstanding Common Stock into a smaller number of shares,
then in each such case the number of votes per share to which holders of shares
of Series A Participating Preferred Stock were entitled immediately prior to
such event shall be adjusted by multiplying such number by a fraction, the
numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event.

                 (B)      Except as otherwise provided herein or by law, the
holders of shares of Series A Participating Preferred Stock and the holders of
shares of Common Stock shall vote together as one class on all matters
submitted to a vote of stockholders of the Corporation.

                 (C)      Except as required by law, holders of Series A
Participating Preferred Stock shall have no special voting rights and their
consent shall not be required (except to the extent they are entitled to vote
with holders of Common Stock as set forth herein) for taking any corporate
action.

         SECTION 4.       CERTAIN RESTRICTIONS.

                 (A)      The Corporation shall not declare any dividend on,
make any distribution on, or redeem or purchase or otherwise acquire for
consideration any shares of Common Stock after the first issuance of a share or
fraction of a share of Series A Participating Preferred Stock unless
concurrently therewith it shall declare a dividend on the Series A
Participating Preferred Stock as required by Section 2 hereof.

                 (B)      Whenever quarterly dividends or other dividends or
distributions payable on the Series A Participating Preferred Stock as provided
in Section 2 are in arrears, thereafter and until all accrued and unpaid
dividends and distributions, whether or not declared, on shares of Series A
Participating Preferred Stock outstanding shall have been paid in full, the
Corporation shall not

                          (i)     declare or pay dividends on, make any other
distributions on, or redeem or purchase or otherwise acquire for consideration
any shares of stock ranking junior (either as to dividends or upon liquidation,
dissolution or winding up) to the Series A Participating Preferred Stock;





                                      A-3
<PAGE>   44
                          (ii)    declare or pay dividends on, make any other
distributions on any shares of stock ranking on a parity (either as to
dividends or upon liquidation, dissolution or winding up) with Series A
Participating Preferred Stock, except dividends paid ratably on the Series A
Participating Preferred Stock and all such parity stock on which dividends are
payable or in arrears in proportion to the total amounts to which the holders
of all such shares are then entitled;

                          (iii)   redeem or purchase or otherwise acquire for
consideration shares of any stock ranking on a parity (either as to dividends
or upon liquidation, dissolution or winding up) with the Series A Participating
Preferred Stock, provided that the Corporation may at any time redeem, purchase
or otherwise acquire shares of any such parity stock in exchange for shares of
any stock of the Corporation ranking junior (either as to dividends or upon
dissolution, liquidation or winding up) to the Series A Participating Preferred
Stock;

                          (iv)    purchase or otherwise acquire for
consideration any shares of Series A Participating Preferred Stock, or any
shares of stock ranking on a parity with the Series A Participating Preferred
Stock, except in accordance with a purchase offer made in writing or by
publication (as determined by the Board of Directors) to all holders of such
shares upon such terms as the Board of Directors, after consideration of the
respective annual dividend rates and other relative rights and preferences of
the respective series and classes, shall determine in good faith will result in
fair and equitable treatment among the respective series or classes.

                 (C)      The Corporation shall not permit any subsidiary of
the Corporation to purchase or otherwise acquire for consideration any shares
of stock of the Corporation unless the Corporation could, under paragraph (A)
of this Section 4, purchase or otherwise acquire such shares at such time and
in such manner.

         SECTION 5.       REACQUIRED SHARES.  Any shares of Series A
Participating Preferred Stock purchased or otherwise acquired by the
Corporation in any manner whatsoever shall be retired and canceled promptly
after the acquisition thereof.  All such shares shall upon their cancellation
become authorized but unissued shares of Preferred Stock and may be reissued as
part of a new series of Preferred Stock to be created by resolution or
resolutions of the Board of Directors, subject to the conditions and
restrictions on issuance set forth herein.

         SECTION 6.       LIQUIDATION, DISSOLUTION OR WINDING UP.

                 (A)      Upon any liquidation (voluntary or otherwise),
dissolution or winding up of the Corporation, no distribution shall be made to
the holders of shares of stock ranking junior (either as to dividends or upon
liquidation, dissolution or winding up) to the Series A Participating Preferred
Stock unless, prior thereto, the holders of shares of Series A Participating
Preferred Stock shall have received $1,000.00 per share, plus an amount equal
to accrued and unpaid dividends and distributions thereon, whether or not
declared, to the date of such payment (the "Series A Liquidation Preference").
Following the payment





                                      A-4
<PAGE>   45
of the full amount of the Series A Liquidation Preference, no additional
distributions shall be made to the holders of shares of Series A Participating
Preferred Stock unless, prior thereto, the holders of shares of Common Stock
shall have received an amount per share (the "Common Adjustment") equal to the
quotient obtained by dividing (i) the Series A Liquidation Preference by (ii)
1,000 (as appropriately adjusted as set forth in subparagraph (C) below to
reflect such events as stock splits, stock dividends and recapitalization with
respect to the Common Stock) (such number in clause (ii), the "Adjustment
Number").  Following the payment of the full amount of the Series A Liquidation
Preference and the Common Adjustment in respect of all outstanding shares of
Series A Participating Preferred Stock and Common Stock, respectively, holders
of Series A Participating Preferred Stock and holders of shares of Common Stock
shall receive their ratable and proportionate share of the remaining assets to
be distributed in the ratio of the Adjustment Number to 1 with respect to such
Preferred Stock and Common Stock, on a per share basis, respectively.

                 (B)      In the event, however, that there are not sufficient
assets available to permit payment in full to the Series A Liquidation
Preference and the liquidation preferences of all other series of Preferred
Stock, if any, which rank on a parity with the Series A Participating Preferred
Stock, then such remaining assets shall be distributed ratably to the holders
of such parity shares in proportion to their respective liquidation
preferences.  In the event, however, that there are not sufficient assets
available to permit payment in full of the Common Adjustment, then such
remaining assets shall be distributed ratably to the holders of Common Stock.

                 (C)      In the event the Corporation shall at any time after
the Rights Declaration Date (i) declare any dividend on Common Stock payable in
shares of Common Stock, (ii) subdivide the outstanding Common Stock, or (iii)
combine the outstanding Common Stock into a smaller number of shares, then in
each such case the Adjustment Number in effect immediately prior to such event
shall be adjusted by multiplying such Adjustment Number by a fraction the
numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event.

         SECTION 7.       CONSOLIDATION, MERGER, ETC.  In case the Corporation
shall enter into any consolidation, merger, combination or other transaction in
which the shares of Common Stock are exchanged for or changed into other stock
or securities, cash and/or any other property, then in any such case the shares
of Series A Participating Preferred Stock shall at the same time be similarly
exchanged or changed in an amount per share (subject to the provision for
adjustment hereinafter set forth) equal to 1,000 times the aggregate amount of
stock, securities, cash and/or any other property (payable in kind), as the
case may be, into which or for which each share of Common Stock is changed or
exchanged.  In the event the Corporation shall at any time after the Rights
Declaration Date (i) declare any dividend on Common Stock payable in shares of
Common Stock, (ii) subdivide the outstanding Common Stock, or (iii) combine the
outstanding Common Stock into a smaller number of shares, then in each such
case the amount set forth in the preceding sentence with respect to the
exchange or change of shares of Series A Participating Preferred Stock shall be





                                      A-5
<PAGE>   46
adjusted by multiplying such amount by a fraction the numerator of which is the
number of shares of Common Stock outstanding immediately after such event and
the denominator of which is the number of shares of Common Stock that were
outstanding immediately prior to such event.

         SECTION 8.       NO REDEMPTION.  The shares of Series A Participating
Preferred Stock shall not be redeemable.

         SECTION 9.       RANKING.  The Series A Participating Preferred Stock
shall rank junior to all other series of the Corporation's Preferred Stock as
to the payment of dividends and the distribution of assets, unless the terms of
any such series shall provide otherwise.

         SECTION 10.      AMENDMENT.  The Amended and Restated Certificate of
Incorporation of the Corporation shall not be further amended in any manner
which would materially alter or change the powers, preference or special rights
of the Series A Participating Preferred Stock so as to affect them adversely
without the affirmative vote of the holders of a majority or more of the
outstanding shares of Series A Participating Preferred Stock, voting separately
as a class.

         SECTION 11.      FRACTIONAL SHARES.  Series A Participating Preferred
Stock may be issued in fractions of a share which shall entitle the holder, in
proportion to such holder's fractional shares, to exercise voting rights,
receive dividends, participate in distributions and to have the benefit of all
other rights of holders of Series A Participating Preferred Stock.

         RESOLVED FURTHER, that the President or any Vice President and the
Secretary or any Assistant Secretary of this corporation be, and they hereby
are, authorized and directed to prepare and file a Certificate of Designation
of Rights, Preferences and Privileges in accordance with the foregoing
resolution and the provisions of Delaware law and to take such actions as they
may deem necessary or appropriate to carry out the intent of the foregoing
resolution."

         3.      That the authorized number of shares of Preferred Stock of the
Corporation is 5,000,000 and that no such Preferred Stock has been issued.




           [The remainder of this page is intentionally left blank.]





                                      A-6
<PAGE>   47
         We further declare under penalty of perjury that the matters set forth
in the foregoing Certificate of Designation are true and correct of our own
knowledge.

         Executed at San Diego, California on ______________, 1996.




                                 ______________________________________________
                                 David E. Robinson, Chairman, President and CEO




                                 ______________________________________________
                                 William L. Respess, Secretary





                                      A-7
<PAGE>   48
                                   EXHIBIT B

                           FORM OF RIGHTS CERTIFICATE


Certificate No. R-                                                _____ Rights


         NOT EXERCISABLE AFTER SEPTEMBER 13, 2006 OR EARLIER IF TERMINATED BY
         THE COMPANY OR IF THE COMPANY EXCHANGES THE RIGHTS PURSUANT TO THE
         RIGHTS AGREEMENT. THE RIGHTS ARE SUBJECT TO REDEMPTION, AT THE OPTION
         OF THE COMPANY, AT $0.01 PER RIGHT ON THE TERMS SET FORTH IN THE
         RIGHTS AGREEMENT.  UNDER CERTAIN CIRCUMSTANCES, RIGHTS BENEFICIALLY
         OWNED BY AN ACQUIRING PERSON OR AN AFFILIATE OR ASSOCIATE OF AN
         ACQUIRING PERSON (AS SUCH TERMS ARE DEFINED IN THE RIGHTS AGREEMENT)
         AND ANY SUBSEQUENT HOLDER OF SUCH RIGHTS MAY BECOME NULL AND VOID.
         [THE RIGHTS REPRESENTED BY THIS RIGHTS CERTIFICATE ARE OR WERE
         BENEFICIALLY OWNED BY A PERSON WHO WAS OR BECAME AN ACQUIRING PERSON
         OR AN AFFILIATE OR ASSOCIATE OF AN ACQUIRING PERSON (AS SUCH TERMS ARE
         DEFINED IN THE RIGHTS AGREEMENT).  ACCORDINGLY, THIS RIGHTS
         CERTIFICATE AND THE RIGHTS REPRESENTED HEREBY MAY BECOME NULL AND VOID
         IN THE CIRCUMSTANCES SPECIFIED IN SECTION 7(E) OF SUCH RIGHTS
         AGREEMENT.]*


                               RIGHTS CERTIFICATE

                      LIGAND PHARMACEUTICALS INCORPORATED


         This certifies that ______________________, or registered assigns, is
the registered owner of the number of Rights set forth above, each of which
entitles the owner thereof, subject to the terms, provisions and conditions of
the Rights Agreement dated as of September 13, 1996 (the "Rights Agreement"),
between Ligand Pharmaceuticals Incorporated, a Delaware corporation (the
"Company"), and WELLS FARGO BANK N.A.  (the "Rights Agent"), to purchase from
the Company at any time after the Distribution Date (as such term is defined in
the Rights Agreement) and prior to 5:00 P.M., California time, on September 13,
2006 at the office of the Rights Agent designated for such purpose, or at





__________________________

         *       The portion of the legend in bracket shall be inserted only if
applicable and shall replace the preceding sentence.


                                      B-1
<PAGE>   49
the office of its successor as Rights Agent, one one-thousandth of a fully paid
non-assessable share of Series A Participating Preferred Stock, par value $.001
per share, (the "Preferred Shares"), of the Company, at a purchase price of
$0.01 per one-thousandth of a Preferred Share (the "Purchase Price"), upon
presentation and surrender of this Rights Certificate with the Form of Election
to Purchase and related Certificate duly executed.  The number of Rights
evidenced by this Rights Certificate (and the number of one-thousandths of a
Preferred Share which may be purchased upon exercise hereof) set forth above
are the number and Purchase Price as of September 13, 1996, based on the
Preferred Shares as constituted at such date.  As provided in the Rights
Agreement, the Purchase Price and the number and kind of Common Shares or other
securities which may be purchased upon the exercise of the Rights evidenced by
this Rights Certificate are subject to modification and adjustment upon the
happening of certain events.

         This Rights Certificate is subject to all of the terms, provisions and
conditions of the Rights Agreement, which terms, provisions and conditions are
hereby incorporated herein by reference and made a part hereof and to which
Rights Agreement reference is hereby made for a full description of the rights,
limitations of rights, obligations, duties and immunities hereunder of the
Rights Agent, the Company and the holders of the Rights Certificates, which
limitations of rights include the temporary suspension of the exercisability of
such Rights under the specific circumstances set forth in the Rights Agreement.
Copies of the Rights Agreement are on file at the principal executive offices
of the Company and the above-mentioned office of the Rights Agent.

         Subject to the provisions of the Rights Agreement, the Rights
evidenced by this Rights Certificate (i) may be redeemed by the Company, at its
option, at a redemption price of $0.01 per Right or (ii) may be exchanged by
the Company in whole or in part for Common Shares, substantially equivalent
rights or other consideration as determined by the Company.

         This Rights Certificate, with or without other Rights Certificates,
upon surrender at the office of the Rights Agent designated for such purpose,
may be exchanged for another Rights Certificate or Rights Certificates of like
tenor and date evidencing Rights entitling the holder to purchase a like
aggregate amount of securities as the Rights evidenced by the Rights
Certificate or Rights Certificates surrendered shall have entitled such holder
to purchase.  If this Rights Certificate shall be exercised in part, the holder
shall be entitled to receive upon surrender hereof another Rights Certificate
or Rights Certificates for the number of whole Rights not exercised.

         No fractional portion of less than one one-thousandth of a Preferred
Share will be issued upon the exercise of any Right or Rights evidenced hereby
but in lieu thereof a cash payment will be made, as provided in the Rights
Agreement.  No holder of this Rights Certificate, as such, shall be entitled to
vote or receive dividends or be deemed for any purpose the holder of the
Preferred Shares or of any other securities of the Company which may at any
time be issuable on the exercise hereof, nor shall anything contained in the
Rights Agreement or herein be construed to confer upon the





                                      B-2
<PAGE>   50
holder hereof, as such, any of the rights of a stockholder of the Company or
any right to vote for the election of directors or upon any matter submitted to
stockholders at any meeting thereof, or to give or withhold consent to any
corporate action, or to receive notice of meetings or other actions affecting
stockholders (except as provided in the Rights Agreement), or to receive
dividends or subscription rights, or otherwise, until the Right or Rights
evidenced by this Rights Certificate shall have been exercised as provided in
the Rights Agreement.

         This Rights Certificate shall not be valid or obligatory for any
purpose until it shall have been countersigned by the Rights Agent.

         WITNESS the facsimile signature of the proper officers of the Company
and its corporate seal.  Dated as of ___________, 19__.


ATTEST:                        LIGAND PHARMACEUTICALS INCORPORATED



_____________________________  By:_____________________________________________
William L. Respess, Secretary     David E. Robinson, Chairman, President and CEO



Countersigned:


WELLS FARGO BANK N.A.
as Rights Agent


By: _________________________
       Authorized Signature





                                      B-3
<PAGE>   51
                   FORM OF REVERSE SIDE OF RIGHTS CERTIFICATE

                               FORM OF ASSIGNMENT

                (To be executed by the registered holder if such
               holder desires to transfer the Rights Certificate)


FOR VALUE RECEIVED __________________ hereby sells, assigns and transfers unto


____________________________________________________________________________
                 (Please print name and address of transferee)

____________________________________________________________________________
this Rights Certificate, together with all right, title and interest therein,
and does hereby irrevocably constitute and appoint __________________________
Attorney, to transfer the within Rights Certificate on the books of the
within-named Company, with full power of substitution.


Dated: _______________, 19__


                                        ______________________________________
                                        Signature


Signature Guaranteed:

         Signatures must be guaranteed by a member firm of a registered
national securities exchange, a member of the National Association of
Securities Dealers, Inc., or a commercial bank or trust company having an
office or correspondent in the United States.





                                      B-4
<PAGE>   52
                                  CERTIFICATE


         The undersigned hereby certifies by checking the appropriate boxes
that:

                 (i)      this Rights Certificate [ ] is [ ] is not being sold,
assigned and transferred by or on behalf of a Person who is or was an Acquiring
Person, or an Affiliate or Associate of any such Person (as such terms are
defined in the Rights Agreement);

                 (ii)     after due inquiry and to the best knowledge of the
undersigned, it [ ] did [ ] did not acquire the Rights evidenced by this Rights
Certificate from any Person who is, was or subsequently became an Acquiring
Person or an Affiliate or Associate of any such Person.

Dated: _______________, 19__



                                        _______________________________________
                                        Signature


Signature Guaranteed:

         Signatures must be guaranteed by a member firm of a registered
national securities exchange, a member of the National Association of
Securities Dealers, Inc., or a commercial bank or trust company having an
office or correspondent in the United States.





                                      B-5
<PAGE>   53
            FORM OF REVERSE SIDE OF RIGHTS CERTIFICATE -- CONTINUED

                          FORM OF ELECTION TO PURCHASE

                      (To be executed if holder desires to
                        exercise the Rights Certificate)

To:      __________________________________

         The undersigned hereby irrevocably elects to exercise _______________
Rights represented by this Rights Certificate to purchase the number of
one-thousandths of a Preferred Share issuable upon the exercise of such Rights
and requests that certificates for such number of one-thousandths of a 
Preferred Share issued in the name of:

Please insert social security or other identifying number

________________________________________________________________________________
                        (Please print name and address)

________________________________________________________________________________

If such number of Rights shall not be all the Rights evidenced by this Rights
Certificate, a new Rights Certificate for the balance remaining of such Rights
shall be registered in the name of and delivered to:

Please insert social security or other identifying number


________________________________________________________________________________
                        (Please print name and address)

________________________________________________________________________________

Dated: ___________________, 19__



                                        ________________________________________
                                        Signature
Signature Guaranteed:

         Signatures must be guaranteed by a member firm of a registered
national securities exchange, a member of the National Association of
Securities Dealers, Inc., or a commercial bank or trust company having an
office or correspondent in the United States.





                                      B-6
<PAGE>   54
                                  CERTIFICATE


         The undersigned hereby certifies by checking the appropriate boxes
that:

         (1)     the Rights evidenced by this Rights Certificate [ ] are [ ]
are not being exercised by or on behalf of a Person who is or was an Acquiring
Person or an Affiliate or Associate of any such Person (as such terms are
defined in the Rights Agreement);

         (2)     after due inquiry and to the best knowledge of the
undersigned, it [ ] did [ ] did not acquire the Rights evidenced by this Rights
Certificate from any Person who is, was or subsequently became an Acquiring
Person or an Affiliate or Associate of any such Person.

Dated: __________ 19__



                                        ________________________________________
                                        Signature


Signature Guaranteed:

         Signatures must be guaranteed by a member firm of a registered
national securities exchange, a member of the National Association of
Securities Dealers, Inc., or a commercial bank or trust company having an
office or correspondent in the United States.





                                      B-7
<PAGE>   55
            FORM OF REVERSE SIDE OF RIGHTS CERTIFICATE -- CONTINUED


                                     NOTICE


         The signature in the foregoing Forms of Assignment and Election must
conform to the name as written upon the face of this Rights Certificate in
every particular, without alteration or enlargement or any change whatsoever.





                                      B-8
<PAGE>   56
                                   EXHIBIT C

                      LIGAND PHARMACEUTICALS INCORPORATED

                            SHAREHOLDER RIGHTS PLAN

                               Summary of Rights


Distribution Transfer of Rights;  The Board of Directors has declared a 
Rights Certificate                dividend of one Right for each share of 
                                  Ligand Pharmaceuticals Incorporated Common
                                  Stock outstanding.  Prior to the Distribution
                                  Date referred to below, the Rights will be 
                                  evidenced by, and trade with, the certificates
                                  for the Common Stock.  After the Distribution
                                  Date, Ligand Pharmaceuticals Incorporated
                                  (the "Company") will mail Rights certificates
                                  to the Company's stockholders and the Rights
                                  will become transferable apart from the Common
                                  Stock.

Distribution Date:                Rights will separate from the Common Stock 
                                  and become exercisable on the tenth day (or 
                                  such later date as may be determined by a 
                                  majority of the Directors not affiliated with
                                  the acquiring person or group (the "Continuing
                                  Directors")) after a person or group (a) 
                                  acquires beneficial ownership of 20% or more
                                  of the Company's Common Stock or (b) announces
                                  a tender or exchange offer, the consummation 
                                  of which would result in ownership by a 
                                  person or group of 20% or more of the 
                                  Company's Common Stock.
                                  
Preferred Stock Purchasable       After the Distribution Date, each Right will
Upon Exercise of Rights:          entitle the holder to purchase, for $100.00 a
                                  fraction of a share of the Company's Preferred
                                  Stock with economic terms similar to that of 
                                  one share of the Company's Common Stock.





                                      C-1
<PAGE>   57
Flip-In:                          If an acquiror (an "Acquiring Person") obtains
                                  20% or more of the Company's Common Stock 
                                  (other than pursuant to a tender offer deemed
                                  adequate and in the best interests of the
                                  Company and its stockholders by the Board of
                                  Directors (a "Permitted Offer")), then each
                                  Right (other than Rights owned by an Acquiring
                                  Person or its affiliates) will entitle the 
                                  holder thereof to purchase, for the exercise
                                  price, a number of shares of the Company's 
                                  Common Stock having a then current market
                                  value of twice the exercise price.

Flip-Over:                        If, after the Shares Acquisition Date (defined
                                  below), (a) the Company merges into another
                                  entity, (b) an acquiring entity merges into 
                                  the Company or (c) the Company sells more than
                                  50% of the Company's assets or earning power,
                                  then each Right (other than Rights owned by an
                                  Acquiring Person or its affiliates) will 
                                  entitle the holder thereof to purchase, for 
                                  the exercise price, a number of shares of 
                                  Common Stock of the person engaging in the
                                  transaction having a then current market value
                                  of twice the exercise price (unless the 
                                  transaction satisfies certain conditions and
                                  is consummated with a person who acquired 
                                  shares pursuant to a Permitted Offer, in which
                                  case the Rights will expire).
                                  
Exchange Provision:               At any time after an event triggering the
                                  flip-in or flip-over rights and prior to the 
                                  acquisition by the Acquiring Person of 50% or
                                  more of the outstanding Common Stock, the
                                  Board of Directors of the Company may exchange
                                  the Rights (other than Rights owned by the 
                                  Acquiring Person or its affiliates), in whole
                                  or in part, at an exchange ratio of one Common
                                  Share per Right (subject to adjustment).

Redemption of the Rights:         Rights will be redeemable at the Company's
                                  option for $0.01 per Right at any time on or
                                  prior to the tenth day (or such later date
                                  as may be determined by a majority of the 
                                  Continuing Directors) after public 
                                  announcement that a person has acquired 
                                  beneficial ownership of 20% or more of the
                                  Company's Common Stock (the "Shares 
                                  Acquisition Date").





                                      C-2
<PAGE>   58
Expiration of the Rights:         The Rights expire on the earliest of (a)
                                  September 13, 2006, (b) exchange or redemption
                                  of the Rights as described above, or (c) 
                                  consummation of a merger or consolidation 
                                  resulting in expiration of the Rights as
                                  described above.

Amendment of Terms of Rights:     The terms of the Rights and the Rights
                                  Agreement may be amended in any respect 
                                  without the consent of the Rights holders on
                                  or prior to the Distribution Date; thereafter,
                                  the terms of the Rights and the Rights 
                                  Agreement may be amended without the consent
                                  of the Rights holders in order to cure any 
                                  ambiguities or to make changes which do not
                                  adversely affect the interests of Rights 
                                  holders (other than the Acquiring Person).
                                  
Voting Rights:                    Rights will not have any voting rights.

Anti-Dilution Provisions:         Rights will have the benefit of certain
                                  customary anti-dilution provisions.
                                  
Taxes:                            The Rights distribution should not be taxable
                                  for federal income tax purposes.  However,
                                  following an event which renders the Rights
                                  exercisable or upon redemption of the Rights,
                                  stockholders may recognize taxable income.

The foregoing is a summary of certain principal terms of the Stockholder Rights
Plan only and is qualified in its entirety by reference to the detailed terms
of the Rights Agreement dated as of September 13, 1996, between the Company and
the Rights Agent.  Further details of the Rights are contained in a letter that
will be mailed to all the Company's stockholders.





                                      C-3


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