<PAGE>

                                                                     Exhibit 4.1

                                     FORM OF

                                RIGHTS AGREEMENT


                                   dated as of

                                  May 23, 2001


                                     between


                                  MEDAREX, INC.
                            a New Jersey Corporation

                                       and

                           CONTINENTAL STOCK TRANSFER
                                 & TRUST COMPANY
                             a New York Corporation
                                 as Rights Agent




--------------------------------------------------------------------------------
<PAGE>

                                TABLE OF CONTENTS
                                -----------------
<TABLE>
<CAPTION>
                                TABLE OF CONTENTS

Section                                                                                               Page
-------                                                                                               ----
<S>     <C>                                                                                             <C>
Section 1. Certain Definitions...........................................................................2
Section 2. Appointment of Rights Agent...................................................................6
Section 3. Issuance of Rights Certificates...............................................................6
Section 4. Form of Rights Certificates...................................................................8
Section 5. Countersignature and Registration.............................................................9
Section 6. Transfer, Split-Up, Combination and Exchange of Rights Certificates;
           Mutilated, Destroyed, Lost or Stolen Rights Certificates.....................................10
Section 7. Exercise of Rights; Purchase Price; Expiration Date of Rights................................10
Section 8. Cancellation and Destruction of Rights Certificates..........................................12
Section 9. Reservation and Availability of Capital Stock................................................13
Section 10. Preferred Stock Record Date.................................................................14
Section 11. Adjustment of Purchase Price, Number and Kind of Shares or Number of Rights.................15
Section 12. Certificate of Adjusted Purchase Price or Number of Shares..................................23
Section 13. Consolidation, Merger or Sale or Transfer of Assets, Cash Flow or Earning Power.............23
Section 14. Fractional Rights and Fractional Shares.....................................................26
Section 15. Rights of Action............................................................................27
Section 16. Agreement of Rights Holders.................................................................27
Section 17. Rights Certificate Holder Not Deemed a Stockholder..........................................28
Section 18. Concerning the Rights Agent.................................................................28
Section 19. Merger or Consolidation or Change of Name of Rights Agent...................................29
Section 20. Duties of Rights Agent......................................................................29
Section 21. Change of Rights Agent......................................................................31
Section 22. Issuance of New Rights Certificates.........................................................32
Section 23. Redemption and Termination..................................................................33
Section 24. Exchange....................................................................................33
Section 25. Notice of Certain Events....................................................................34
Section 26. Notices.....................................................................................35
Section 27. Supplements and Amendments..................................................................36
Section 28. Successors..................................................................................37
Section 29. Determinations and Actions by the Board of Directors, etc...................................37
Section 30. Benefits of this Agreement..................................................................37
Section 31. Severability................................................................................37
Section 32. Governing Law...............................................................................38
Section 33. Counterparts................................................................................38
Section 34. Descriptive Headings........................................................................38
</TABLE>

<PAGE>

                            FORM OF RIGHTS AGREEMENT
                            ------------------------


          RIGHTS AGREEMENT, dated as of  May 23, 2001 (the "Agreement"), between
Medarex, Inc., a New Jersey corporation (the "Company"), and Continental Stock
Transfer & Trust Company, a New York corporation (the "Rights Agent").

                              W I T N E S S E T H
                              - - - - - - - - - -

          WHEREAS, on May 23, 2001 (the "Rights Dividend Declaration Date"), the
Board of Directors of the Company (the "Board") authorized and declared a
dividend distribution of one Right (as hereinafter defined) for each share of
common stock, par value $0.01 per share, of the Company (the "Common Stock")
outstanding at the close of business on July 6, 2001 (the "Record Date"), and
has authorized the issuance of one Right (as such number may hereafter be
adjusted pursuant to the provisions of Section 11(p) hereof) for each share of
Common Stock issued between the Record Date (whether originally issued or
delivered from the Company's treasury) and the earlier of the Distribution Date
and the Expiration Date (as such terms are hereinafter defined) each Right
initially representing the right to purchase one one-thousandth of a share of
Series A Junior Participating Preferred Stock of the Company (the "Preferred
Stock") having the rights, powers and preferences set forth in the form of
Certificate of Amendment attached hereto as Exhibit A, upon the terms and
subject to the conditions hereinafter set forth (the "Rights");

          NOW, THEREFORE, in consideration of the premises 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 twenty percent (20%) or more of the shares of Common Stock
then outstanding, but shall not include (i) the Company, (ii) any Subsidiary of
the Company, (iii) any employee benefit plan of the Company, or of any
Subsidiary of the Company, or any Person or entity organized, appointed or
established by the Company for or pursuant to the terms of any such plan, or
(iv) any Person, together with all Affiliates and Associates of such Person, who
or which would be an Acquiring Person solely by reason of being the Beneficial
Owner of shares of Common Stock, the Beneficial Ownership of which was acquired
by such Person pursuant to any action or transaction or series of related
actions or transactions approved by the Board of Directors before such Person
otherwise became an Acquiring Person.

               (b) "Act" shall mean the Securities Act of 1933.

                                       2
<PAGE>

               (c) "Adjustment Shares" shall have the meaning set forth in
Section 11(a)(ii) hereof.

               (d) "Affiliate" and "Associate" shall have the respective
meanings ascribed to such terms in Rule 12b-2 of the General Rules and
Regulations under the Exchange Act.

               (e) 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, directly or indirectly, has the right to acquire (whether
          such right is exercisable immediately or only after the passage of
          time) pursuant to any agreement, arrangement or understanding (whether
          or not in writing) or upon the exercise of conversion rights, exchange
          rights, rights, warrants or options, or otherwise; provided, however,
                                                             --------  -------
          that a Person shall not be deemed the "Beneficial Owner" of, or to
          "beneficially own," (A) securities tendered pursuant to a tender or
          exchange offer made by such Person or any of such Person's Affiliates
          or Associates until such tendered securities are accepted for purchase
          or exchange, (B) securities issuable upon exercise of Rights at any
          time prior to the occurrence of a Triggering Event (as hereinafter
          defined), or (C) securities issuable upon exercise of Rights from and
          after the occurrence of a Triggering Event which Rights were acquired
          by such Person or any of such Person's Affiliates or Associates prior
          to the Distribution Date (as hereinafter defined) or pursuant to
          Section 3(a) or Section 22 hereof (the "Original Rights") or pursuant
          to Section 11(i) hereof in connection with an adjustment made with
          respect to any Original Rights;

                    (ii) which such Person or any of such Person's Affiliates or
          Associates, directly or indirectly, has the right to vote or dispose
          of or has "beneficial ownership" of (as determined pursuant to Rule
          13d-3 of the General Rules and Regulations under the Exchange Act),
          including pursuant to any agreement, arrangement or understanding,
          whether or not in writing; provided, however, that a Person shall not
                                     --------  -------
          be deemed the "Beneficial Owner" of, or to "beneficially own," any
          security under this subparagraph (ii) as a result of an agreement,
          arrangement or understanding to vote such security if such agreement,
          arrangement or understanding: (A) arises solely from a revocable proxy
          given in response to a public proxy or consent solicitation made
          pursuant to, and in accordance with, the applicable provisions of the
          General Rules and Regulations under the Exchange Act, and (B) is not
          also then reportable by such Person 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

                                       3
<PAGE>

          which such Person (or any of such Person's Affiliates or Associates)
          has any agreement, arrangement or understanding (whether or not in
          writing), for the purpose of acquiring, holding, voting (except
          pursuant to a revocable proxy as described in the proviso to
          subparagraph (ii) of this paragraph (d)) or disposing of any voting
          securities of the Company; provided, however, that nothing in this
          paragraph (d) shall cause a Person engaged in business as an
          underwriter of securities to be the "Beneficial Owner" of, or to
          "beneficially own," any securities acquired through such Person's
          participation in good faith in a firm commitment underwriting until
          the expiration of forty days after the date of such acquisition, and
          then only if such securities continue to be owned by such Person at
          such expiration of forty days and provided further, however, that any
                                            -------- -------  -------
          stockholder of the Company, with affiliate(s), associate(s) or other
          person(s) who may be deemed representatives of it serving as
          director(s) of the Company, shall not be deemed to beneficially own
          securities held by other Persons as a result of (i) persons affiliated
          or otherwise associated with such stockholder serving as directors or
          taking any action in connection therewith, (ii) discussing the status
          of its shares with the Company or other stockholders of the Company
          similarly situated or (iii) voting or acting in a manner similar to
          other stockholders similarly situated, absent a specific finding by
          the Board of Directors of an express agreement among such stockholders
          to act in concert with one another as stockholders so as to cause, in
          the good faith judgment of the Board of Directors, each such
          stockholder to be the Beneficial Owner of the shares held by the other
          stockholder(s).

               (f) "Business Day" shall mean any day other than a Saturday,
Sunday or a day on which banking institutions in the State of New Jersey are
authorized or obligated by law or executive order to close.

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

               (h) "Common Stock" shall mean the common stock, par value $0.01
per share, of the Company, except that "Common Stock" when used with reference
to any Person other than the Company shall mean the capital stock of such Person
with the greatest voting power, or the equity securities or other equity
interest having power to control or direct the management, of such Person.

               (i) "Common Stock Equivalents" shall have the meaning set forth
in Section 11(a)(iii) hereof.

               (j) "Current Market Price" shall have the meaning set forth in
Section 11(d)(i) hereof.

                                       4
<PAGE>

               (k) "Current Value" shall have the meaning set forth in Section
11(a)(iii) hereof.

               (l) "Distribution Date" shall have the meaning set forth in
Section 3(a) hereof.

               (m) "Equivalent Preferred Stock" shall have the meaning set forth
in Section 11(b) hereof.

               (n) "Exchange Act" shall mean the Securities and Exchange Act of
1934, as amended and in effect on the date of this Agreement.

               (o) "Exchange Ratio" shall have the meaning set forth in Section
24 hereof.

               (p) "Expiration Date" shall have the meaning set forth in Section
7(a) hereof.

               (q) "Final Expiration Date" shall have the meaning set forth in
Section 7(a) hereof.

               (r) "Person" shall mean any individual, firm, corporation,
partnership or other entity.

               (s) "Preferred Stock" shall mean shares of Series A Junior
Participating Preferred Stock, par value $1 per share, of the Company, and, to
the extent that there are not a sufficient number of shares of Series A Junior
Participating Preferred Stock authorized to permit the full exercise of the
Rights, any other series of preferred stock of the Company designated for such
purpose containing terms substantially similar to the terms of the Series A
Junior Participating Preferred Stock.

               (t) "Principal Party" shall have the meaning set forth in Section
13(b) hereof.

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

               (v) "Qualified Offer" shall have the meaning set forth in Section
11(a)(ii) hereof.

               (w) "Record Date" shall have the meaning set forth in the WHEREAS
clause at the beginning of this Agreement.

               (x) "Rights" shall have the meaning set forth in the WHEREAS
clause at the beginning of this Agreement.

               (y) "Rights Agent" shall have the meaning set forth in the
parties clause at the beginning of this Agreement.

                                       5
<PAGE>

               (z) "Rights Certificate" shall have the meaning set forth in
Section 3(a) hereof.

               (aa) "Rights Dividend Declaration Date" shall have the meaning
set forth in the WHEREAS clause at the beginning of this Agreement.

               (bb) "Section 11(a)(ii) Event" shall mean any event described in
Section 11(a)(ii) hereof.

               (cc) "Section 13 Event" shall mean any event described in clauses
(x), (y) or (z) of Section 13(a) hereof.

               (dd) "Spread" shall have the meaning set forth in Section
11(a)(iii) hereof.

               (ee) "Stock Acquisition Date" shall mean the first date of public
announcement (which, for purposes of this definition, shall include, without
limitation, a report filed or amended pursuant to Section 13(d) under the
Exchange Act) by the Company or an Acquiring Person that an Acquiring Person has
become such, other than pursuant to a Qualified Offer.

               (ff) "Subsidiary" shall mean, with reference to any Person, any
corporation of which an amount of voting securities sufficient to elect at least
a majority of the directors of such corporation is beneficially owned, directly
or indirectly, by such Person, or otherwise controlled by such Person.

               (gg) "Substitution Period" shall have the meaning set forth in
Section 11(a)(iii) hereof.

               (hh) "Summary of Rights" shall have the meaning set forth in
Section 3(b) hereof.

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

               (jj) "Triggering Event" shall mean any Section 11(a)(ii) Event or
any Section 13 Event.

       Section 2. Appointment of Rights Agent. The Company hereby appoints the
                  ---------------------------
Rights Agent to act as agent for the Company 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 earlier of (i) the close of business on the tenth
Business Day after the Stock Acquisition Date (or, if the tenth Business Day
after the

                                       6
<PAGE>

Stock Acquisition Date occurs before the Record Date, the close of business on
the Record Date), or (ii) the close of business on the tenth Business Day (or
such later date as the Board shall determine) 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
Company, or any Person or entity organized, appointed or established by the
Company for or pursuant to the terms of any such plan) is commenced within the
meaning of Rule 14d-2(a) of the General Rules and Regulations under the Exchange
Act, if upon consummation thereof, such Person would become an Acquiring Person,
in either instance other than pursuant to a Qualified Offer (the earlier of (i)
and (ii) being herein referred to as the "Distribution Date"), (x) the Rights
will be evidenced (subject to the provisions of paragraph (b) of this Section 3)
by the certificates for the Common Stock registered in the names of the holders
of the Common Stock (which certificates for Common Stock shall be deemed also to
be certificates for Rights) and not by separate certificates, and (y) the Rights
will be transferable only in connection with the transfer of the underlying
shares of Common Stock (including a transfer to the Company). As soon as
practicable after the Distribution Date, the Rights Agent will send by
first-class, insured, postage-prepaid mail, to each record holder of the Common
Stock as of the close of business on the Distribution Date, at the address of
such holder shown on the records of the Company, one or more right certificates,
in substantially the form of Exhibit B hereto (the "Rights Certificates"),
evidencing one Right for each share of Common Stock so held, subject to
adjustment as provided herein. In the event that an adjustment in the number of
Rights per share of Common Stock has been made pursuant to Section 11(p) hereof,
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
and after the Distribution Date, the Rights will be evidenced solely by such
Rights Certificates.

               (b) The Company will make available, as promptly as practicable
following the Record Date, a copy of a summary of the Rights, in substantially
the form attached hereto as Exhibit C (the "Summary of Rights") to any holder
Rights who may so request from time to time prior to the Expiration Date. With
respect to certificates for the Common Stock outstanding as of the Record Date,
until the Distribution Date, the Rights will be evidenced by such certificates
for the Common Stock and the registered holders of the Common Stock shall also
be the registered holders of the associated Rights. Until the earlier of the
Distribution Date or the Expiration Date (as such term is defined in Section
7(a) hereof), the transfer of any certificates representing shares of Common
Stock in respect of which Rights have been issued shall also constitute the
transfer of the Rights associated with such shares of Common Stock.

               (c) Rights shall be issued in respect of all shares of Common
Stock which are issued (whether originally issued or from the Company's
treasury) after the Record Date but prior to the earlier of the Distribution
Date or the Expiration Date. Certificates representing such shares of Common
Stock shall also be deemed to be certificates for Rights, and shall bear the
following legend:

                                       7
<PAGE>

               This certificate also evidences and entitles the holder hereof to
     certain Rights as set forth in the Rights Agreement between Medarex, Inc.
     (the "Company") and the Rights Agent thereunder (the "Rights Agreement"),
     the terms of which are hereby incorporated herein by reference and a copy
     of which is on file at the principal offices of the Rights Agent.  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.  The Rights Agent will mail to the holder of this
     certificate a copy of the Rights Agreement, as in effect on the date of
     mailing,  without charge, promptly 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 Stock represented by such certificates shall be
evidenced by such certificates alone and registered holders of Common Stock
shall also be the registered holders of the associated Rights, and the transfer
of any of such certificates shall also constitute the transfer of the Rights
associated with the Common Stock represented by such certificates.

       Section 4. Form of Rights Certificates.
                  ----------------------------

               (a) The Rights Certificates (and the forms of election to
purchase and of assignment to be printed on the reverse thereof) shall each be
substantially in the form set forth in 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 and on their face shall entitle the holders thereof
to purchase such number of one one-thousandths of a share of Preferred Stock as
shall be set forth therein at the price set forth therein (such exercise price
per one one-thousandth of a share, the "Purchase Price"), but the amount and
type of securities purchasable upon the exercise of each Right and the Purchase
Price thereof shall be subject to adjustment as provided herein.

               (b) Any Rights Certificate issued pursuant to Section 3(a),
Section 11(i) 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

                                       8
<PAGE>

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 President or any Vice President,
either manually or by facsimile signature, and shall have affixed thereto the
Company's seal or a facsimile thereof which shall be attested by the Secretary
or an Assistant Secretary of the Company, either manually or by facsimile
signature. The Rights Certificates shall be countersigned by the Rights Agent,
either manually or by facsimile signature, and shall not be valid for any
purpose unless so 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 Certificates 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 to be kept, at its principal office or offices designated as the
appropriate place for surrender of Rights Certificates upon exercise or
transfer, 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.

                                       9
<PAGE>

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

               (a) Subject to the provisions of Section 4(b), Section 7(e) and
Section 14 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 Certificates (other than Rights Certificates representing
Rights that may have been exchanged pursuant to Section 24 hereof) may be
transferred, split up, combined or exchanged for another Rights Certificate or
Certificates, entitling the registered holder to purchase a like number of one
one-thousandths of a share of Preferred Stock (or, following a Triggering Event,
Common Stock, other securities, cash or other assets, as the case may be) as the
Rights Certificate or Certificates surrendered then entitles such holder (or
former holder in the case of a transfer) to purchase. Any registered holder
desiring to transfer, split up, combine or exchange any Rights Certificate or
Certificates shall make such request in writing delivered to the Rights Agent,
and shall surrender the Rights Certificate or Certificates to be transferred,
split up, combined or exchanged at the principal office or offices 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 Section 4(b), Section 7(e), Section
14 hereof and Section 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 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 execute and deliver a new Rights Certificate of like
tenor to the Rights Agent for countersignature and delivery to the registered
owner 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 Section 7(e) hereof, at any time after the
Distribution Date the registered holder of any Rights Certificate may exercise
the Rights evidenced thereby (except as otherwise provided herein including,
without limitation, the restrictions on exercisability set forth in Section
9(c), Section 11(a)(iii) and Section 23(a) hereof) in whole or in part upon
surrender of the Rights Certificate, with the form of

                                       10
<PAGE>

election to purchase and the certificate on the reverse side thereof duly
executed, to the Rights Agent at the principal office or offices of the Rights
Agent designated for such purpose, together with payment of the aggregate
Purchase Price with respect to the total number of one one-thousandths of a
share (or other securities, cash or other assets, as the case may be) as to
which such surrendered Rights are then exercisable, at or prior to the earlier
of (i) 5:00 P.M., Princeton, New Jersey time, on July 6, 2011, or such later
date as may be established by the Board of Directors prior to the expiration of
the Rights (such date, as it may be extended by the Board, the ("Final
Expiration Date")), or (ii) the time at which the Rights are redeemed or
exchanged as provided in Section 23 and Section 24 hereof (the earlier of (i)
and (ii) being herein referred to as the "Expiration Date").

               (b) The Purchase Price for each one one-thousandth of a share of
Preferred Stock pursuant to the exercise of a Right shall initially be one
hundred and fifty dollars ($150), and shall be subject to adjustment from time
to time as provided in Section 11 and Section 13(a) hereof and shall be payable
in accordance with paragraph (c) below.

               (c) Upon receipt of a Rights Certificate representing exercisable
Rights, with the form of election to purchase and the certificate duly executed,
accompanied by payment, with respect to each Right so exercised, of the Purchase
Price per one one-thousandth of a share of Preferred Stock (or other shares,
securities, cash or other assets, as the case may be) to be purchased as set
forth below and an amount equal to any applicable transfer tax, the Rights Agent
shall, subject to Section 20(k) hereof, thereupon promptly (i) (A) requisition
from any transfer agent of the shares of Preferred Stock (or make available, if
the Rights Agent is the transfer agent for such shares) certificates for the
total number of one one- thousandths of a share of Preferred Stock 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 shares of Preferred Stock issuable upon exercise of
the Rights hereunder with a depositary agent, requisition from the depositary
agent depositary receipts representing such number of one one-thousandths of a
share of Preferred Stock as are to be purchased (in which case certificates for
the shares of Preferred Stock represented by such receipts shall be deposited by
the transfer agent with the depositary agent) and the Company will direct the
depositary agent to comply with such request, (ii) requisition from the Company
the amount of cash, if any, to be paid in lieu 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) after receipt thereof, deliver
such cash, if any, 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
pursuant to Section 11(a)(iii) hereof) shall 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 (including Common Stock) 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. The Company reserves the right to require
prior to the occurrence of a Triggering Event

                                       11
<PAGE>

that, upon any exercise of Rights, a number of Rights be exercised so that only
whole shares of Preferred Stock would be issued.

               (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 and 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, subject to the provisions of Section 14 hereof.

               (e) Notwithstanding anything in this Agreement to the contrary,
from and after the first occurrence of a Section 11(a)(ii) 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, 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
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),
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 any other Person as a result of its failure to make
any determinations with respect to an Acquiring Person or its 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 any of its
agents, be delivered to the Rights Agent for cancellation or in cancelled form,
or, if surrendered to the Rights Agent, shall be cancelled 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

                                       12
<PAGE>

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 cancelled Rights Certificates to the Company, or shall, at the written
request of the Company, destroy such cancelled Rights Certificates, and in such
case shall deliver a certificate of destruction thereof to the Company.

       Section 9. Reservation and Availability of Capital Stock.
                  ---------------------------------------------

               (a) The Company covenants and agrees that it will cause to be
reserved and kept available out of its authorized and unissued shares of
Preferred Stock (and, following the occurrence of a Triggering Event, out of its
authorized and unissued shares of Common Stock and/or other securities or out of
its authorized and issued shares held in its treasury), the number of shares of
Preferred Stock (and, following the occurrence of a Triggering Event, Common
Stock and/or other securities) that, as provided in this Agreement including
Section 11(a)(iii) hereof, will be sufficient to permit the exercise in full of
all outstanding Rights.

               (b) So long as the shares of Preferred Stock (and, following the
occurrence of a Triggering Event, Common Stock and/or other securities) issuable
and deliverable upon the exercise of the Rights may be listed on any national
securities exchange, the Company shall use its best efforts to cause, from and
after such time as the Rights become exercisable, 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
Section 11(a)(ii) Event on which the consideration to be delivered by the
Company upon exercise of the Rights has been determined in accordance with
Section 11(a)(iii) hereof, a registration statement under the 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
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 the expiration of the
Rights. 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. The Company may
temporarily suspend, for a period of time 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 that the exercisability of the
Rights has been temporarily suspended, as well as a public announcement at such
time as the suspension has been rescinded. In addition, if the Company shall
determine that a registration statement is required following the Distribution
Date, the Company may temporarily suspend the exercisability of the Rights until
such time as a registration statement has been declared effective.
Notwithstanding any provision of this Agreement to the contrary, the Rights
shall not be exercisable in any jurisdiction if the requisite qualification in
such

                                       13
<PAGE>

jurisdiction shall not have been obtained, the exercise thereof shall not be
permitted under applicable law, or a registration statement shall not have been
declared effective.

               (d) The Company covenants and agrees that it will take all such
action as may be necessary to ensure that all one one-thousandths of a share of
Preferred Stock (and, following the occurrence of a Triggering Event, Common
Stock and/or other securities) delivered upon exercise of Rights shall, at the
time of delivery of the certificates for such shares (subject to payment of the
Purchase Price), be duly and validly authorized and issued and fully paid and
nonassessable.

               (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 issuance or delivery of the Rights
Certificates and of any certificates for a number of one one-thousandths of a
share of Preferred Stock (or Common Stock and/or other securities, as the case
may be) 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 a number of one one-thousandths of a share of Preferred Stock (or
Common Stock and/or other securities, as the case may be) in respect of a name
other than that of the registered holder of the Rights Certificates evidencing
Rights surrendered for exercise or to issue or deliver any certificates for a
number of one one-thousandths of a share of Preferred Stock (or Common Stock
and/or other securities, as the case may be) in a name other than that of the
registered holder upon the exercise of any Rights until 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 Stock Record Date. Each person in whose name any
                   ----------------------------
certificate for a number of one one-thousandths of a share of Preferred Stock
(or Common Stock and/or other securities, as the case may be) is issued upon the
exercise of Rights shall for all purposes be deemed to have become the holder of
record of such fractional shares of Preferred Stock (or Common Stock and/or
other securities, as the case may be) 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
(and all applicable transfer taxes) was made; provided, however, that if the
                                              --------  -------
date of such surrender and payment is a date upon which the Preferred Stock (or
Common Stock and/or other securities, as the case may be) transfer books of the
Company are closed, such Person shall be deemed to have become the record holder
of such shares (fractional or otherwise) on, and such certificate shall be
dated, the next succeeding Business Day on which the Preferred Stock (or Common
Stock and/or other securities, as the case may be) 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 stockholder of the
Company with respect to 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.

                                       14
<PAGE>

       Section 11. Adjustment of Purchase Price, Number and Kind of Shares or
                   ----------------------------------------------------------
Number of Rights. The Purchase Price, the number and kind of shares 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 Preferred Stock
          payable in shares of Preferred Stock, (B) subdivide the outstanding
          Preferred Stock, (C) combine the outstanding Preferred Stock into a
          smaller number of shares, or (D) issue any shares of its capital stock
          in a reclassification of the Preferred Stock (including any such
          reclassification in connection with a consolidation or merger in which
          the Company is the continuing or surviving corporation), except as
          otherwise provided in this Section 11(a) and Section 7(e) hereof, 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, and the number and kind of shares of Preferred Stock
          or capital stock, as the case may be, issuable on such date, shall be
          proportionately adjusted so that the holder of any Right exercised
          after such time shall be entitled to receive, upon payment of the
          Purchase Price then in effect, the aggregate number and kind of shares
          of Preferred Stock or capital stock, as the case may be, which, if
          such Right had been exercised immediately prior to such date and at a
          time when the Preferred Stock transfer books of the Company were open,
          such holder would have owned upon such exercise and been entitled to
          receive by virtue of such dividend, subdivision, combination or
          reclassification. 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) In the event any Person shall, at any time after the
          Rights Dividend Declaration Date, become an Acquiring Person, unless
          the event causing such Person to become an Acquiring Person is a
          transaction set forth in Section 13(a) hereof, or is an acquisition of
          shares of Common Stock pursuant to a tender offer or an exchange offer
          for all outstanding shares of Common Stock at a price and on terms
          determined by at least a majority of the members of the Board of
          Directors who are not officers of the Company and who are not
          representatives, nominees, Affiliates or Associates of an Acquiring
          Person, after receiving advice from one or more investment banking
          firms, to be (a) at a price which is fair to stockholders and not
          inadequate (taking into account all factors which such members of the
          Board deem relevant, including, without limitation, prices which could
          reasonably be achieved if the Company or its assets were sold on an
          orderly basis designed to realize maximum value) and (b) otherwise in
          the best interests of the Company and its stockholders (a "Qualified
          Offer").

                                       15
<PAGE>

then, promptly following the occurrence of such event, proper provision shall be
made so that each holder of a Right (except as provided below and in Section
7(e) hereof) shall thereafter have the right to receive, upon exercise thereof
at the then current Purchase Price in accordance with the terms of this
Agreement, in lieu of a number of one one-thousandths of a share of Preferred
Stock, such number of shares of Common Stock of the Company as shall equal the
result obtained by (x) multiplying the then current Purchase Price by the then
number of one one-thousandths of a share of Preferred Stock for which a Right
was exercisable immediately prior to the first occurrence of a Section 11(a)(ii)
Event, and (y) dividing that product (which, following such first occurrence,
shall thereafter be referred to as the "Purchase Price" for each Right and for
all purposes of this Agreement) by fifty percent (50%) of the Current Market
Price (determined pursuant to Section 11(d) hereof) per share of Common Stock on
the date of such first occurrence (such number of shares, the "Adjustment
Shares").

                    (iii) In the event that the number of shares of Common Stock
          which are authorized by the Company's Restated Certificate of
          Incorporation, but which are 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 in accordance
          with the foregoing subparagraph (ii) of this Section 11(a), the
          Company shall (A) determine the value of the Adjustment Shares
          issuable upon the exercise of a Right (the "Current Value"), and (B)
          with respect to each Right (subject to Section 7(e) hereof), make
          adequate provision to substitute for the Adjustment Shares, upon the
          exercise of a Right and payment of the applicable Purchase Price, (1)
          cash, (2) a reduction in the Purchase Price, (3) Common Stock or other
          equity securities of the Company (including, without limitation,
          shares, or units of shares, of preferred stock, such as the Preferred
          Stock, which the Board has deemed to have essentially the same value
          or economic rights as shares of Common Stock (such shares of preferred
          stock being referred to as "Common Stock Equivalents")), (4) debt
          securities of the Company, (5) other assets, or (6) any combination of
          the foregoing, having an aggregate value equal to the Current Value
          (less the amount of any reduction in the Purchase Price), where such
          aggregate value has been determined by the Board based upon the advice
          of a nationally recognized investment banking firm selected by the
          Board; provided, however, that 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 Section 11(a)(ii) 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, shares of Common Stock (to
          the extent available) and then, if necessary, cash, which shares
          and/or cash have an aggregate value equal to the Spread. For purposes
          of the preceding sentence, the

                                       16
<PAGE>

          term "Spread" shall mean the excess of (i) the Current Value over (ii)
          the Purchase Price. If the Board determines in good faith that it is
          likely that sufficient additional shares of Common Stock could be
          authorized for issuance upon exercise in full of the Rights, 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 (such thirty
          (30) day period, as it may be extended, is herein called the
          "Substitution Period"). To the extent that action is to be taken
          pursuant to the first and/or third sentences of this Section
          11(a)(iii), the Company (1) shall provide, subject to Section 7(e)
          hereof, that such action shall apply uniformly to all outstanding
          Rights, and (2) may suspend the exercisability of the Rights until the
          expiration of the Substitution Period in order to seek such
          stockholder approval for such authorization of additional shares
          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 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)(iii), the value of each Adjustment Share shall be the current
          market price per share of the Common Stock on the Section 11(a)(ii)
          Trigger Date and the per share or per unit value of any Common Stock
          Equivalent shall be deemed to equal the current market price per share
          of the Common Stock on such date.

               (b) In case the Company shall fix a record date for the issuance
of rights, options or warrants to all holders of Preferred Stock entitling them
to subscribe for or purchase (for a period expiring within forty-five (45)
calendar days after such record date) Preferred Stock (or shares having the same
rights, privileges and preferences as the shares of Preferred Stock ("Equivalent
Preferred Stock")) or securities convertible into Preferred Stock or Equivalent
Preferred Stock at a price per share of Preferred Stock or per share of
Equivalent Preferred Stock (or having a conversion price per share, if a
security convertible into Preferred Stock or Equivalent Preferred Stock) less
than the Current Market Price (as determined pursuant to Section 11(d) hereof)
per share of Preferred Stock on such record date, 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 shares of Preferred Stock outstanding
on such record date, plus the number of shares of Preferred Stock which the
aggregate offering price of the total number of shares of Preferred Stock and/or
Equivalent Preferred Stock 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 shares of Preferred Stock outstanding on such record date, plus the number of
additional shares of Preferred Stock and/or Equivalent Preferred Stock 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 by delivery of consideration,

                                       17
<PAGE>

part or all of which may 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. Shares of Preferred Stock 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 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 fix a record date for a
distribution to all holders of Preferred Stock (including any such distribution
made in connection with a consolidation or merger in which the Company is the
continuing corporation) of evidences of indebtedness, cash (other than a regular
quarterly cash dividend out of the earnings or retained earnings of the
Company), assets (other than a dividend payable in Preferred Stock, but
including any dividend payable in stock other than Preferred Stock) or evidences
of indebtedness, or of subscription rights or warrants (excluding those referred
to in Section 11(b) hereof), 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 Current Market Price (as determined pursuant to Section 11(d)
hereof) per share of Preferred Stock on such record date, less the fair market
value (as determined in good faith by the Board of Directors of the Company,
whose determination shall be 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 share of
Preferred Stock, and the denominator of which shall be such Current Market Price
(as determined pursuant to Section 11(d) hereof) per share of Preferred Stock.
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)(i) For the purpose of any computation hereunder, other
          than computations made pursuant to Section 11(a)(iii) hereof, the
          Current Market Price per share of Common Stock on any date shall be
          deemed to be the average of the daily closing prices per share of such
          Common Stock for the thirty (30) consecutive Trading Days immediately
          prior to such date, and for purposes of computations made pursuant to
          Section 11(a)(iii) hereof, the Current Market Price per share of
          Common Stock on any date shall be deemed to be the average of the
          daily closing prices per share of such Common Stock for the ten (10)
          consecutive Trading Days immediately following such date; provided,
                                                                    --------
          however, that in the event that the Current Market Price per share of
          -------
          the Common Stock is determined during a period following the
          announcement by the issuer of such Common Stock of (A) a dividend or
          distribution on such Common Stock payable in shares of such Common
          Stock or securities convertible into shares of such Common Stock
          (other than the Rights), or (B) any subdivision, combination or
          reclassification of such Common Stock, and

                                       18
<PAGE>

          the ex-dividend date for such dividend or distribution, or the record
          date for such subdivision, combination or reclassification shall not
          have occurred prior to the commencement of the requisite thirty (30)
          Trading Day or ten (10) Trading Day period, as set forth above, then,
          and in each such case, the Current Market Price shall be properly
          adjusted to take into account ex-dividend trading. 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 shares of Common Stock are 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 shares of Common
          Stock are listed or admitted to trading or, if the shares of Common
          Stock are not listed or admitted to trading on any national securities
          exchange, the last quoted price or, if not so quoted, 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 Automated
          Quotation System ("NASDAQ") or such other system then in use, or, if
          on any such date the shares of Common Stock are 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 Common
          Stock selected by the Board. If on any such date no market maker is
          making a market in the Common Stock, the fair value of such shares on
          such date as determined in good faith by the Board shall be used. The
          term "Trading Day" shall mean a day on which the principal national
          securities exchange on which the shares of Common Stock are listed or
          admitted to trading is open for the transaction of business or, if the
          shares of Common Stock are not listed or admitted to trading on any
          national securities exchange, a Business Day. If the Common Stock is
          not publicly held or not so listed or traded, Current Market Price per
          share shall mean the fair value per share as determined in good faith
          by the Board, whose determination shall be described in a statement
          filed with the Rights Agent and shall be conclusive for all purposes.

                    (ii) For the purpose of any computation hereunder, the
          Current Market Price per share of Preferred Stock shall be determined
          in the same manner as set forth above for the Common Stock in clause
          (i) of this Section 11(d) (other than the last sentence thereof). If
          the Current Market Price per share of Preferred Stock cannot be
          determined in the manner provided above or if the Preferred Stock is
          not publicly held or listed or traded in a manner described in clause
          (i) of this Section 11(d), the Current Market Price per share of
          Preferred Stock shall be conclusively deemed to be an amount equal to
          one thousand (1000) (as such number may be appropriately adjusted for
          such events as stock splits, stock dividends and recapitalizations
          with respect to the Common Stock

                                       19
<PAGE>

          occurring after the date of this Agreement) multiplied by the Current
          Market Price per share of the Common Stock. If neither the Common
          Stock nor the Preferred Stock is publicly held or so listed or traded,
          Current Market Price per share of the Preferred Stock shall mean the
          fair value per share as determined in good faith by the Board, whose
          determination shall be described in a statement filed with the Rights
          Agent and shall be conclusive for all purposes. For all purposes of
          this Agreement, the Current Market Price of a Unit shall be equal to
          the Current Market Price of one share of Preferred Stock divided by
          one thousand (1000).

               (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 one percent (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 share of
Common Stock or other share or one-millionth of a share of Preferred Stock, 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 mandates such
adjustment, or (ii) the Expiration Date.

               (f) If as a result of an adjustment made pursuant to Section
11(a)(ii) or Section 13(a) hereof, the holder of any Right thereafter exercised
shall become entitled to receive any shares of capital stock other than
Preferred Stock, thereafter the number of such other shares so receivable upon
exercise of any Right and 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 Preferred Stock contained in
Sections 11(a), (b), (c), (e), (g), (h), (i), (j), (k) and (m), and the
provisions of Sections 7, 9, 10, 13 and 14 hereof with respect to the Preferred
Stock 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 one-thousandths of a
share of Preferred Stock 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 Sections 11(b) and (c), 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
one one-thousandths of a share of Preferred Stock (calculated to the nearest
one-millionth) obtained by (i) multiplying (x) the number of one one-thousandths
of a share covered by a Right immediately prior to this adjustment, by (y) the
Purchase Price in effect immediately prior to such adjustment of

                                       20
<PAGE>

the Purchase Price, and (ii) dividing the product so obtained by the Purchase
Price in effect immediately after such adjustment of the Purchase Price.

               (i) The Company may elect on or after the date of any adjustment
of the Purchase Price to adjust the number of Rights, in lieu of any adjustment
in the number of one one-thousandths of a share of Preferred Stock purchasable
upon the exercise of a Right. Each of the Rights outstanding after the
adjustment in the number of Rights shall be exercisable for the number of one
one-thousandths of a share of Preferred Stock 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-ten-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 one one-thousandths of a share of Preferred Stock
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 share and the number of one one-thousandths of a 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 then stated value, if any, of the number
of one one-thousandths of a share of Preferred Stock 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 fully paid and nonassessable such number of one one- thousandths
of a share of Preferred Stock at such adjusted Purchase Price.

                                       21
<PAGE>

               (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 issuance to the holder of any Right exercised after such record date
the number of one one-thousandths of a share of Preferred Stock and other
capital stock or securities of the Company, if any, issuable upon such exercise
over and above the number of one one-thousandths of a share of Preferred Stock
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) or securities upon the occurrence of
the event requiring such adjustment.

               (m) Anything in this Section 11 to the contrary notwithstanding,
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 in their good faith judgment the Board of Directors of the
Company shall determine to be advisable in order that any (i) consolidation or
subdivision of the Preferred Stock, (ii) issuance wholly for cash of any shares
of Preferred Stock at less than the Current Market Price, (iii) issuance wholly
for cash of shares of Preferred Stock or securities which by their terms are
convertible into or exchangeable for shares of Preferred Stock, (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 Stock
shall not be taxable to such stockholders.

               (n) The Company covenants and agrees that it shall not, at any
time after the Distribution Date, (i) consolidate with any other Person (other
than a Subsidiary of the Company in a transaction which complies with Section
11(o) hereof), (ii) merge with or into any other Person (other than a Subsidiary
of the Company in a transaction which complies with Section 11(o) hereof), or
(iii) sell or transfer (or permit any Subsidiary to sell or transfer), in one
transaction, or a series of related transactions, assets, cash flow or earning
power aggregating more than fifty percent (50%) 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 and/or any of its Subsidiaries in one or more
transactions each of which complies with Section 11(o) hereof), if (x) at the
time of or immediately after such consolidation, merger or sale 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 (y) prior to, simultaneously with or
immediately after such consolidation, merger or sale, the shareholders of the
Person who constitutes, or would constitute, the "Principal Party" for purposes
of Section 13(a) 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 Section 23 or Section 26 hereof, take
(or permit any Subsidiary to take) any action if at the time such action is
taken it is

                                       22
<PAGE>

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 that the Company shall at any time after the Rights Dividend
Declaration Date and prior to the Distribution Date (i) declare a dividend on
the outstanding shares of Common Stock payable in shares of Common Stock, (ii)
subdivide the outstanding shares of Common Stock, or (iii) combine the
outstanding shares of Common Stock into a smaller number of shares, the number
of Rights associated with each share of Common Stock then outstanding, or issued
or delivered thereafter but prior to the Distribution Date, shall be
proportionately adjusted so that the number of Rights thereafter associated with
each share of Common Stock following any such event shall equal the result
obtained by multiplying the number of Rights associated with each share of
Common Stock immediately prior to such event by a fraction the numerator which
shall be the total number of shares of Common Stock outstanding immediately
prior to the occurrence of the event and the denominator of which shall be the
total number of shares of Common Stock outstanding immediately following the
occurrence of such event.

       Section 12. Certificate of Adjusted Purchase Price or Number of Shares.
                   -----------------------------------------------------------
Whenever an adjustment is made as provided in Section 11 and Section 13 hereof,
the Company shall (a) promptly prepare a certificate setting forth such
adjustment and a brief statement of the facts accounting for such adjustment,
(b) promptly file with the Rights Agent, and with each transfer agent for the
Preferred Stock and the Common Stock, a copy of such certificate and (c) if a
Distribution Date has occurred, mail a brief summary thereof to each holder of a
Rights Certificate in accordance with Section 27 hereof. The Rights Agent shall
be fully protected in relying on any such certificate and on any adjustment
therein contained.

       Section 13. Consolidation, Merger or Sale or Transfer of Assets, Cash
                   ---------------------------------------------------------
Flow or Earning Power.
----------------------

               (a) In the event that, following the Stock Acquisition Date,
directly or indirectly, (x) the Company shall consolidate with, or merge with
and into, any other Person (other than a Subsidiary of the Company in a
transaction which complies with Section 11(o) hereof), and the Company shall not
be the continuing or surviving corporation of such consolidation or merger, (y)
any Person (other than a Subsidiary of the Company in a transaction which
complies with Section 11(o) hereof) shall consolidate with, or merge with or
into, the Company, and the Company shall be the continuing or surviving
corporation of such consolidation or merger and, in connection with such
consolidation or merger, all or part of the outstanding shares of Common Stock
shall be changed into or exchanged for stock or other securities of any other
Person or cash or any other property, or (z) the Company shall sell or otherwise
transfer (or one or more of its Subsidiaries shall sell or otherwise transfer),
in one transaction or a series of related transactions, assets, cash flow or
earning power aggregating more than fifty percent (50%) of the assets, cash flow
or earning power of the Company and its Subsidiaries (taken as a whole) to any
Person or Persons (other than the Company or any

                                       23
<PAGE>

Subsidiary of the Company in one or more transactions each of which complies
with Section 11(o) hereof), then, and in each such case (except as may be
contemplated by Section 13(d) hereof), proper provision shall be made so that:
(i) each holder of a Right, except as provided in Section 7(e) hereof, shall
thereafter have the right to receive, upon the exercise thereof at the then
current Purchase Price in accordance with the terms of this Agreement, such
number of validly authorized and issued, fully paid, non-assessable and freely
tradable shares of Common Stock of the Principal Party (as such term is
hereinafter defined), not subject to 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 one-
thousandths of a share of Preferred Stock for which a Right is exercisable
immediately prior to the first occurrence of a Section 13 Event (or, if a
Section 11(a)(ii) Event has occurred prior to the first occurrence of a Section
13 Event, multiplying the number of such one one-thousandths of a share for
which a Right was exercisable immediately prior to the first occurrence of a
Section 11(a)(ii) Event by the Purchase Price in effect immediately prior to
such first occurrence), and dividing that product (which, following the first
occurrence of a Section 13 Event, shall be referred to as the "Purchase Price"
for each Right and for all purposes of this Agreement) by (2) fifty percent
(50%) of the Current Market Price (determined pursuant to Section 11(d)(i)
hereof) per share of the Common Stock of such Principal Party on the date of
consummation of such Section 13 Event; (ii) 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; (iii)
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; (iv) such Principal Party shall take such steps (including, but not
limited to, the reservation of a sufficient number of shares of its Common
Stock) 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 shares of Common Stock
thereafter deliverable upon the exercise of the Rights; and (v) the provisions
of Section 11(a)(ii) hereof shall be of no effect following the first occurrence
of any Section 13 Event.

               (b) "Principal Party" shall mean:

                    (i) in the case of any transaction described in clause (x)
          or (y) of the first sentence of Section 13(a), the Person that is the
          issuer of any securities into which shares of Common Stock of the
          Company are converted in such merger or consolidation, and if no
          securities are so issued, the Person that is the other party to such
          merger or consolidation; and

                    (ii) in the case of any transaction described in clause (z)
          of the first sentence of Section 13(a), the Person that is the party
          receiving the greatest portion of the assets, cash flow or earning
          power transferred pursuant to such transaction or transactions;

                                       24
<PAGE>

provided, however, that in any such case, (1) if the Common Stock of such Person
--------  -------
is not at such time and has not been continuously over the preceding twelve (12)
month period registered under Section 12 of the Exchange Act, and such Person is
a direct or indirect Subsidiary of another Person the Common Stock of which is
and has been so registered, "Principal Party" shall refer to such other Person;
and (2) in case such Person is a Subsidiary, directly or indirectly, of more
than one Person, the Common Stocks of two or more of which are and have been so
registered, "Principal Party" shall refer to whichever of such Persons is the
issuer of the Common Stock having the greatest aggregate market value.

               (c) The Company shall not consummate any such consolidation,
merger, sale or transfer unless the Principal Party shall have a sufficient
number of authorized shares of its Common Stock which 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 Principal
Party shall have executed and delivered to the Rights Agent a supplemental
agreement providing for the terms set forth in paragraphs (a) and (b) of this
Section 13 and further providing that, as soon as practicable after the date of
any consolidation, merger or sale of assets mentioned in paragraph (a) of this
Section 13, the Principal Party will

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

                    (ii) take such all such other action as may be necessary to
          enable the Principal Party to issue the securities purchasable upon
          exercise of the Rights, including but not limited to the registration
          or qualification of such securities under all requisite securities
          laws of jurisdictions of the various states and the listing of such
          securities on such exchanges and trading markets as may be necessary
          or appropriate; and

                    (iii) will deliver to holders of the Rights historical
          financial statements for the Principal Party and each of its
          Affiliates which comply in all respects with the requirements for
          registration on Form 10 under the Exchange Act.

The provisions of this Section 13 shall similarly apply to successive mergers or
consolidations or sales or other transfers.  In the event that a Section 13
Event shall occur at any time after the occurrence of a Section 11(a)(ii) Event,
the Rights which have not theretofore been exercised shall thereafter become
exercisable in the manner described in Section 13(a).

               (d) Notwithstanding anything in this Agreement to the contrary,
Section 13 shall not be applicable to a transaction described in subparagraphs

                                       25
<PAGE>

(x) and (y) of Section 13(a) if (i) such transaction is consummated with a
Person or Persons who acquired shares of Common Stock pursuant to a tender offer
or exchange offer for all outstanding shares of Common Stock which is a
Qualified Offer as such term is defined in Section 11(a)(ii) hereof (or a wholly
owned subsidiary of any such Person or Persons), (ii) the price per share of
Common Stock offered in such transaction is not less than the price per share of
Common Stock paid to all holders of shares of Common Stock whose shares were
purchased pursuant to such tender offer or exchange offer and (iii) the form of
consideration being offered to the remaining holders of shares of Common Stock
pursuant to such transaction is the same as the form of consideration paid
pursuant to such tender offer or exchange offer.

       Section 14. Fractional Rights and Fractional Shares.
                   ----------------------------------------

               (a) The Company shall not be required to issue fractions of
Rights, except prior to the Distribution Date as provided in Section 11(p)
hereof, or to distribute Rights Certificates which evidence fractional Rights.
In lieu of such fractional Rights, the Company shall pay 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 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. The closing price of the Rights for
any 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 Rights are 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 Rights are listed or
admitted to trading, or if the Rights are not listed or admitted to trading on
any national securities exchange, the last quoted price or, if not so quoted,
the average of the high bid and low asked prices in the over-the-counter market,
as reported by NASDAQ or such other system then in use or, if on any such date
the Rights are 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 Rights, selected by the Board of Directors of the Company. If on any such
date no such market maker is making a market in the Rights, the fair value of
the Rights on such date as determined in good faith by the Board of Directors of
the Company shall be used.

               (b) The Company shall not be required to issue fractions of
shares of Preferred Stock (other than fractions which are integral multiples of
one one- thousandth of a share of Preferred Stock) upon exercise of the Rights
or to distribute certificates which evidence fractional shares of Preferred
Stock (other than fractions which are integral multiples of one one-thousandth
of a share of Preferred Stock). In lieu of fractional shares of Preferred Stock
that are not integral multiples of one one-thousandth of a share of Preferred
Stock, the Company may pay to the registered holders of Rights Certificates at
the time such Rights are exercised as herein provided an amount

                                       26
<PAGE>

in cash equal to the same fraction of the current market value of one
one-thousandth of a share of Preferred Stock. For purposes of this Section
14(b), the current market value of one one-thousandth of a share of Preferred
Stock shall be one one-thousandth of the closing price of a share of Preferred
Stock (as determined pursuant to Section 11(d)(ii) hereof) for the Trading Day
immediately prior to the date of such exercise.

               (c) Following the occurrence of a Triggering Event, the Company
shall not be required to issue fractions of shares of Common Stock upon exercise
of the Rights or to distribute certificates which evidence fractional shares of
Common Stock. In lieu of fractional shares of Common Stock, the Company may pay
to the registered holders 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 one (1) share of Common Stock. For purposes of this
Section 14(c), the current market value of one share of Common Stock shall be
the closing price of one share of Common Stock (as determined pursuant to
Section 11(d)(i) hereof) for the Trading Day immediately prior to the date of
such exercise.

               (d) The holder of a Right by the acceptance of the Rights
expressly waives his right to receive any fractional Rights or any fractional
shares upon exercise of a Right, except as permitted by this Section 14.

       Section 15. Rights of Action. All rights of action in respect of this
                   -----------------
Agreement are vested in the respective registered holders of the Rights
Certificates (and, prior to the Distribution Date, the registered holders of the
Common Stock); and any registered holder of any Rights Certificate (or, prior to
the Distribution Date, of the Common Stock), 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 Stock), may, in his own behalf and for his 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 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 shall be entitled to specific performance
of the obligations hereunder and injunctive relief against actual or threatened
violations of the obligations hereunder 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 Common Stock;

               (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

                                       27
<PAGE>

accompanied by a proper instrument of transfer and with the appropriate forms
and certificates fully executed;

               (c) subject to Section 6(a) and Section 7(f) hereof, the Company
and the Rights Agent may deem and treat the person in whose name a Rights
Certificate (or, prior to the Distribution Date, the associated Common Stock
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 Stock certificate made by anyone
other than the Company or the Rights Agent) for all purposes whatsoever, and
neither the Company nor the Rights Agent, subject to the last sentence of
Section 7(e) hereof, shall be required to be affected by any notice to the
contrary; and

               (d) notwithstanding anything in this Agreement to the contrary,
neither the Company nor the Rights Agent shall have any liability to any holder
of a Right or other Person as a result of its inability to perform any of its
obligations under this Agreement by reason of any preliminary or permanent
injunction or other order, decree or ruling issued by a court of competent
jurisdiction or by a governmental, regulatory or administrative agency or
commission, or any statute, rule, regulation or executive order promulgated or
enacted by any governmental authority, prohibiting or otherwise restraining
performance of such obligation; provided, however, the Company must use its best
                                --------  -------
efforts to have any such order, decree or ruling lifted or otherwise overturned
as soon as possible.

       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 number of one
one-thousandths of a share of Preferred Stock 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
disbursements 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

                                       28
<PAGE>

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.

               (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 Common Stock 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.

       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, stock transfer or other shareholder services business of
the Rights Agent or any successor Rights Agent, shall be the successor to the
Rights Agent under this Agreement without the execution or filing of any paper
or any further act on the part of any of the parties hereto; but only if 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 a 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 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:

                                       29
<PAGE>

               (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 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
the Chairman of the Board, the President, any Vice President, the Treasurer, the
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 only for its own
negligence, bad faith or willful misconduct.

               (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 or be required to verify the same (except as to its
countersignature on such Rights Certificates), 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 adjustment required under the provisions of
Section 11, Section 13 or Section 24 hereof or responsible for the manner,
method or amount of any such adjustment or the ascertaining of the existence of
facts that would require any such adjustment (except with respect to the
exercise of Rights evidenced by Rights Certificates after actual notice of any
such adjustment); nor shall it by any act hereunder be deemed to make any
representation or warranty as to the authorization or reservation of any shares
of Common Stock or Preferred Stock to be issued pursuant to this Agreement or
any Rights Certificate or as to whether any shares of Common Stock or Preferred
Stock will, when so 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.

                                       30
<PAGE>

               (g) The Rights Agent is hereby authorized and directed to accept
instructions with respect to the performance of its duties hereunder from the
Chairman of the Board, the President, any Vice President, the Secretary, any
Assistant Secretary, the Treasurer or any Assistant Treasurer 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 to be taken
by it in good faith in accordance with instructions of any such officer.

               (h) The Rights Agent and any stockholder, director, officer or
employee 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, however, 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 Common Stock and Preferred Stock, by registered or
certified mail, and, if such resignation occurs after the Distribution Date, to
the registered holders of the Rights Certificates by first-class

                                       31
<PAGE>

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 Common Stock
and Preferred Stock, by registered or certified mail, and, if such removal
occurs after the Distribution Date, 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 Rights Certificate for inspection by the Company),
then any 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
legal business entity organized and doing business under the laws of the United
States or of the State of California or of any other state of the United States,
in good standing, having an office in the State of California, which is
authorized under such laws to exercise corporate trust or stock transfer or
shareholder services powers and which has at the time of its appointment as
Rights Agent a combined capital and surplus of at least $50,000,000 or (b) an
affiliate of a legal business entity described in clause (a) of this sentence.
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 Common Stock
and the Preferred Stock, and, if such appointment occurs after the Distribution
Date, 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 the 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 shares of Common Stock following the Distribution
Date and prior to the redemption or expiration of the Rights, the Company (a)
shall, with respect to shares of Common Stock so issued or sold pursuant to the
exercise of stock options or under any employee plan or arrangement, granted or
awarded as of the Distribution Date, or upon the exercise, conversion or
exchange of securities hereafter 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 if, and to the extent that, the Company shall
be advised by counsel that such issuance would create a significant risk of
material adverse tax consequences to the Company or the Person to whom such
Rights

                                       32
<PAGE>

Certificate would be issued, 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 and Termination.
                   ---------------------------

               (a) The Board of Directors of the Company may, at its option, at
any time prior to the earlier of (i) the close of business on the tenth Business
Day following the Stock Acquisition Date (or, if the Stock Acquisition Date
shall have occurred prior to the Record Date, the close of business on the tenth
Business Day following the Record Date), or (ii) the Final Expiration Date,
redeem all but not less than all of the then outstanding Rights at a redemption
price of $.001 per Right, as such amount may be appropriately adjusted to
reflect any stock split, stock dividend or similar transaction occurring after
the date hereof (such redemption price being hereinafter referred to as the
"Redemption Price"). Notwithstanding anything contained in this Agreement to the
contrary, the Rights shall not be exercisable after the first occurrence of a
Section 11(a)(ii) Event until such time as the Company's right of redemption
hereunder has expired. The Company may, at its option, pay the Redemption Price
in cash, shares of Common Stock (based on the Current Market Price, as defined
in Section 11(d)(i) hereof, of the Common Stock at the time of redemption) or
any other form of consideration deemed appropriate by the Board of 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 for
each Right so held. Promptly 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 each holder's last address as it appears 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 Stock. 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.

       Section 24. Exchange.
                   ---------

               (a) The Board of Directors of the Company may, at its option, at
any time after any Person becomes an Acquiring Person, 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
Stock at an exchange ratio of one share of Common Stock 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 "Exchange Ratio"). Notwithstanding the foregoing, the Board of
Directors of the Company 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

                                       33
<PAGE>

Common Stock for or pursuant to the terms of any such plan), together with all
Affiliates and Associates of such Person, becomes the Beneficial Owner of fifty
percent (50%) or more of the Common Stock then outstanding.

               (b) Immediately upon the action of the Board of Directors of the
Company 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 shares of Common Stock equal
to the number of such Rights held by such holder multiplied by the Exchange
Ratio. The Company shall promptly 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 promptly 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 Stock 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 any exchange pursuant to this Section 24, the Company, at
its option, may substitute Preferred Stock (or Equivalent Preferred Stock, as
such term is defined in paragraph (b) of Section 11 hereof) for Common Stock
exchangeable for Rights, at the initial rate of one one-thousandth of a share of
Preferred Stock (or Equivalent Preferred Stock) for each share of Common Stock,
as appropriately adjusted to reflect stock splits, stock dividends and other
similar transactions after the date hereof.

               (d) In the event that there shall not be sufficient shares of
Common Stock issued but not outstanding or authorized but unissued to permit any
exchange of Rights as contemplated in accordance with this Section 24, the
shares of Company shall take all such action as may be necessary to authorize
additional shares of Common Stock for issuance upon exchange of the Rights.

               (e) The Company shall not be required to issue fractions of
shares of Common Stock or to distribute certificates which evidence fractional
shares of Common Stock. In lieu of such fractional shares of Common Stock, there
shall be paid to the registered holders of the Rights Certificates with regard
to which such fractional shares of Common Stock would otherwise be issuable, an
amount in cash equal to the same fraction of the current market value of a whole
share of Common Stock. For the purposes of this subsection (e), the current
market value of a whole share of Common Stock shall be the closing price of a
share of Common Stock (as determined pursuant to the second sentence of Section
11(d)(i) hereof) for the Trading Day immediately prior to the date of exchange
pursuant to this Section 24.

                                       34
<PAGE>

       Section 25. Notice of Certain Events.
                   -------------------------

               (a) In case the Company shall propose, at any time after the
Distribution Date, (i) to pay any dividend payable in stock of any class to the
holders of Preferred Stock or to make any other distribution to the holders of
Preferred Stock (other than a regular quarterly cash dividend out of earnings or
retained earnings of the Company), or (ii) to offer to the holders of Preferred
Stock rights or warrants to subscribe for or to purchase any additional shares
of Preferred Stock or shares of stock of any class or any other securities,
rights or options, or (iii) to effect any reclassification of its Preferred
Stock (other than a reclassification involving only the subdivision of
outstanding shares of Preferred Stock), or (iv) to effect any consolidation or
merger into or with any other Person (other than a Subsidiary of the Company in
a transaction which complies with Section 11(o) hereof), or to effect any sale
or other transfer (or to permit one or more of its Subsidiaries to effect any
sale or other transfer), in one transaction or a series of related transactions,
of more than fifty percent (50%) of the assets, cash flow or earning power of
the Company and its Subsidiaries (taken as a whole) to any other Person or
Persons (other than the Company and/or any of its Subsidiaries in one or more
transactions each of which complies with Section 11(o) hereof), or (v) to effect
the liquidation, dissolution or winding up of the Company, then, in each such
case, the Company shall give to each holder of a Rights Certificate, to the
extent feasible and in accordance with Section 26 hereof, a notice of such
proposed action, which shall specify the record date for the purposes of such
stock dividend, distribution of rights or warrants, or the date on which such
reclassification, consolidation, merger, sale, transfer, liquidation,
dissolution, or winding up is to take place and the date of participation
therein by the holders of the shares of Preferred Stock, if any such date is to
be fixed, and such notice shall be so given in the case of any action covered by
clause (i) or (ii) above at least twenty (20) days prior to the record date for
determining holders of the shares of Preferred Stock for purposes of such
action, and in the case of any such other action, at least twenty (20) days
prior to the date of the taking of such proposed action or the date of
participation therein by the holders of the shares of Preferred Stock whichever
shall be the earlier.

               (b) In case any of the events set forth in Section 11(a)(ii)
hereof shall occur, then, in any such case, (i) the Company shall as soon as
practicable thereafter give to each holder of a Rights Certificate, to the
extent feasible and 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 Section 11(a)(ii) hereof, and (ii) all
references in the preceding paragraph to Preferred Stock shall be deemed
thereafter to refer to Common Stock and/or, if appropriate, other securities.

       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 by
the Rights Agent with the Company) as follows:


                Medarex, Inc.
                707 State Road, Suite 206
                Princeton, NJ 08540-1437
                Attention:  Corporate Secretary

                                       35
<PAGE>

Subject to the provisions of Section 21, 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 by the Rights Agent with the Company) as follows:


                Continental Stock Transfer and Trust Company
                2 Broadway, 19th Floor
                New York, NY 10004
                Attention:  Corporate Trust Department


          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 (or, if
prior to the Distribution Date, to the holder of certificates representing
shares of Common Stock) 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,
                   ---------------------------
and subject to the penultimate sentence of this Section 27, the Company and the
Rights Agent shall, if the Company so directs, supplement or amend any provision
of this Agreement without the approval of any holders of certificates
representing shares of Common Stock. From and after the Distribution Date, the
Company and the Rights Agent shall, if the Company so directs, supplement or
amend this Agreement without the approval of any holders of Rights Certificates
in order (i) to cure any ambiguity, (ii) to correct or supplement any provision
contained herein which may be defective or inconsistent with any other
provisions herein, (iii) to shorten or lengthen any time period hereunder, or
(iv) to change or supplement the provisions hereunder in any manner which the
Company may deem necessary or desirable and which shall not adversely affect the
interests of the holders of Rights Certificates (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 any time period hereunder other
than a time period related to when the Rights may be redeemed, pursuant to
clause (iii) of this sentence, 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 which 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 Stock. Notwithstanding anything herein to the contrary, this
Agreement may not be amended at a time when the Rights are not redeemable.

                                       36
<PAGE>

       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 shares of
Common Stock outstanding at any particular time, including for purposes of
determining the particular percentage of such outstanding shares of Common Stock
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 shall have the
exclusive power and authority to administer this Agreement and to exercise all
rights and powers specifically granted to the Board or to the Company, 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
in good faith, shall (x) be final, conclusive and binding on the Company, the
Rights Agent, the holders of the Rights and all other parties, and (y) not
subject the Board, or any of the directors on the Board 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, registered holders of the Common Stock) 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, registered holders of the Common Stock).

       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 Business Day following the date of such determination by the Board of
Directors. Without limiting the foregoing, if any provision requiring a specific
group of Directors of the Company to act is held to by any court of competent
jurisdiction or other authority to be invalid, void or unenforceable, such
determination shall then be made by the Board of Directors of the Company in

                                       37
<PAGE>

accordance with applicable law and the Company's Restated Certificate of
Incorporation and Bylaws.

       Section 32. Governing Law. This Agreement, each Right and each Rights
                   --------------
Certificate issued hereunder shall be deemed to be a contract made under the
laws of the State of New Jersey and for all purposes shall be governed by and
construed in accordance with the laws of such State applicable to contracts made
and to be 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.

                                       38
<PAGE>

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


                                    MEDAREX, INC.


                                    By________________________________________
                                    Name:
                                    Title:


                                    CONTINENTAL STOCK TRANSFER & TRUST COMPANY


                                    By________________________________________
                                    Name:
                                    Title:


                                       39
<PAGE>

                                                                       Exhibit A
                                                                       ---------


                                     FORM OF
             CERTIFICATE OF AMENDMENT OF THE RESTATED CERTIFICATE OF
           INCORPORATION OF MEDAREX, INC. SETTING FORTH THE TERMS OF
                  SERIES A JUNIOR PARTICIPATING PREFERRED STOCK

                                       of

                                 MEDAREX, INC.


                Pursuant to Section 14A:7-2(4) of the New Jersey
                            Business Corporation Act


          We, Irwin Lerner, Chairman of the Board, and Donald L. Drakeman,
President, and Chief Executive Officer of Medarex, Inc., a corporation organized
and existing under the Business Corporation Act of the State of New Jersey, in
accordance with the provisions of Section 14A:7-2(4) thereof, DO HEREBY CERTIFY:

          That pursuant to the authority conferred upon the Board of Directors
by the Restated Certificate of Incorporation of the said Corporation, the said
Board of Directors adopted the following resolution creating a series of 250,000
shares of Preferred Stock designated as Series A Junior Participating Preferred
Stock:

          RESOLVED, that pursuant to the authority vested in the Board of
Directors of this Corporation in accordance with the provisions of its
Certificate of Incorporation, a series of Preferred Stock of the Corporation be
and it hereby is created, and that the designation and amount thereof and the
voting powers, preferences and relative, participating, optional and other
special rights of the shares of such series, and the qualifications, limitations
or restrictions thereof are as follows:

          Section 1. Designation and Amount.  The shares of such series shall be
                     ----------------------
designated as "Series A Junior Participating Preferred Stock" and the number of
shares constituting such series shall be 250,000.

          Section 2. Dividends and Distributions.
                     ---------------------------

          (A) Subject to the prior and superior rights of the holders of any
shares of any series of Preferred Stock ranking prior and superior to the shares
of Series A Junior Participating Preferred Stock with respect to dividends, the
holders of shares of Series A Junior 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 March 31, June 30, September 30, and December 31 in each year (each such
date being referred to herein as a "Quarterly
<PAGE>

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 Junior
Participating Preferred Stock, in an amount per share (rounded to the nearest
cent) equal to the greater of (a) $.01 or (b) subject to the provision for
adjustment hereinafter set forth, one thousand (1000) times the aggregate per
share amount of all cash dividends, and one thousand (1000) 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, par value $0.01 per share, 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
Junior Participating Preferred Stock. In the event the Corporation shall at any
time after May 23, 2001 (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 Junior Participating Preferred Stock were entitled
immediately prior to such event under clause (b) of 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 Junior 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); provided that, in the
event no dividend or distribution shall have been declared on the Common Stock
during the period between any Quarterly Dividend Payment Date and the next
subsequent Quarterly Dividend Payment Date, a dividend of $.01 per share on the
Series A Junior Participating Preferred Stock shall nevertheless be payable on
such subsequent Quarterly Dividend Payment Date.

          (C) Dividends shall begin to accrue and be cumulative on outstanding
shares of Series A Junior Participating Preferred Stock from the Quarterly
Dividend Payment Date next preceding the date of issue of such shares of Series
A Junior 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 Junior 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 Junior 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

                                       2
<PAGE>

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 Junior 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 Junior
                     -------------
Participating Preferred Stock shall have the following voting rights:

         (A) Subject to the provision for adjustment hereinafter set forth, each
share of Series A Junior Participating Preferred Stock shall entitle the holder
thereof to one thousand (1000) 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 Junior 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 Junior 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) (i) If at any time dividends on any Series A Junior
         Participating Preferred Stock shall be in arrears in an amount equal to
         six (6) quarterly dividends thereon, the occurrence of such contingency
         shall mark the beginning of a period (herein called a "default period")
         which shall extend until such time when all accrued and unpaid
         dividends for all previous quarterly dividend periods and for the
         current quarterly dividend period on all shares of Series A Junior
         Participating Preferred Stock then outstanding shall have been declared
         and paid or set apart for payment. During each default period, all
         holders of Preferred Stock (including holders of the Series A Junior
         Participating Preferred Stock) with dividends in arrears in an amount
         equal to six (6) quarterly dividends thereon, voting as a class,
         irrespective of series, shall have the right to elect two (2)
         directors.

                  (ii) During any default period, such voting right of the
         holders of Series A Junior Participating Preferred Stock may be
         exercised initially at a special meeting called pursuant to
         subparagraph (iii) of this Section 3(C) or at any annual meeting of
         stockholders, and thereafter at annual meetings of stockholders,
         provided that neither such voting right nor the right of the holders of
         any other series of Preferred Stock, if any, to increase, in certain
         cases, the authorized number of

                                       3
<PAGE>

         directors shall be exercised unless the holders of ten percent (10%) in
         number of shares of Preferred Stock outstanding shall be present in
         person or by proxy. The absence of a quorum of the holders of Common
         Stock shall not affect the exercise by the holders of Preferred Stock
         of such voting right. At any meeting at which the holders of Preferred
         Stock shall exercise such voting right initially during an existing
         default period, they shall have the right, voting as a class, to elect
         directors to fill such vacancies, if any, in the Board of Directors as
         may then exist up to two (2) directors or, if such right is exercised
         at an annual meeting, to elect two (2) directors. If the number which
         may be so elected at any special meeting does not amount to the
         required number, the holders of the Preferred Stock shall have the
         right to make such increase in the number of directors as shall be
         necessary to permit the election by them of the required number. After
         the holders of the Preferred Stock shall have exercised their right to
         elect directors in any default period and during the continuance of
         such period, the number of directors shall not be increased or
         decreased except by vote of the holders of Preferred Stock as herein
         provided or pursuant to the rights of any equity securities ranking
         senior to or pari passu with the Series A Junior Participating
         Preferred Stock.

                  (iii) Unless the holders of Preferred Stock shall, during an
         existing default period, have previously exercised their right to elect
         directors, the Board of Directors may order, or any stockholder or
         stockholders owning in the aggregate not less than ten percent (10%) of
         the total number of shares of Preferred Stock outstanding, irrespective
         of series, may request, the calling of a special meeting of the holders
         of Preferred Stock, which meeting shall thereupon be called by the
         President, a Vice-President or the Secretary of the Corporation. Notice
         of such meeting and of any annual meeting at which holders of Preferred
         Stock are entitled to vote pursuant to this Paragraph (C)(iii) shall be
         given to each holder of record of Preferred Stock by mailing a copy of
         such notice to him at his last address as the same appears on the books
         of the Corporation. Such meeting shall be called for a time not earlier
         than 20 days and not later than 60 days after such order or request or
         in default of the calling of such meeting within 60 days after such
         order or request, such meeting may be called on similar notice by any
         stockholder or stockholders owning in the aggregate not less than ten
         percent (10%) of the total number of shares of Preferred Stock
         outstanding. Notwithstanding the provisions of this Paragraph (C)(iii),
         no such special meeting shall be called during the period within 60
         days immediately preceding the date fixed for the next annual meeting
         of the stockholders.

                  (iv) In any default period, the holders of Common Stock, and
         other classes of stock of the Corporation if applicable, shall continue
         to be entitled to elect the whole number of directors until the holders
         of Preferred Stock shall have exercised their right to elect two (2)
         directors voting as a class, after the exercise of which

                                       4
<PAGE>

         right (x) the directors so elected by the holders of Preferred Stock
         shall continue in office until their successors shall have been elected
         by such holders or until the expiration of the default period, and (y)
         any vacancy in the Board of Directors may (except as provided in
         Paragraph (C)(ii) of this Section 3) be filled by vote of a majority of
         the remaining directors theretofore elected by the holders of the class
         of stock which elected the director whose office shall have become
         vacant. References in this Paragraph (C) to directors elected by the
         holders of a particular class of stock shall include directors elected
         by such directors to fill vacancies as provided in clause (y) of the
         foregoing sentence.

                  (v) Immediately upon the expiration of a default period, (x)
         the right of the holders of Preferred Stock as a class to elect
         directors shall cease, (y) the term of any directors elected by the
         holders of Preferred Stock as a class shall terminate, and (z) the
         number of directors shall be such number as may be provided for in the
         Amended and Restated Certificate of Incorporation or Bylaws
         irrespective of any increase made pursuant to the provisions of
         Paragraph (C)(ii) of this Section 3 (such number being subject,
         however, to change thereafter in any manner provided by law or in the
         certificate of incorporation or by-laws). Any vacancies in the Board of
         Directors effected by the provisions of clauses (y) and (z) in the
         preceding sentence may be filled by a majority of the remaining
         directors.

         (D) Except as set forth herein, holders of Series A Junior
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) Whenever quarterly dividends or other dividends or distributions
payable on the Series A Junior 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 Junior
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 Junior
         Participating Preferred Stock;

                  (ii) declare or pay dividends on or 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 the
         Series A Junior Participating Preferred Stock, except dividends paid
         ratably on

                                       5
<PAGE>

         the Series A Junior 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 Junior 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 Junior
         Participating Preferred Stock; or

                  (iv) purchase or otherwise acquire for consideration any
         shares of Series A Junior Participating Preferred Stock, or any shares
         of stock ranking on a parity with the Series A Junior 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.

         (B) 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 Junior
                     -----------------
Participating Preferred Stock purchased or otherwise acquired by the Corporation
in any manner whatsoever shall be retired and cancelled 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.  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 Junior Participating Preferred Stock unless, prior
thereto, the holders of shares of Series A Junior Participating Preferred Stock
shall have received an amount equal to one thousand times the purchase price per
share of Series A Participating Preferred Stock, 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 of the full

                                       6
<PAGE>

amount of the Series A Liquidation Preference, no additional distributions shall
be made to the holders of shares of Series A Junior 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) 1000 (as
appropriately adjusted as set forth in subparagraph (C) below to reflect such
events as stock splits, stock dividends and recapitalizations 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
Junior Participating Preferred Stock and Common Stock, respectively, holders of
Series A Junior 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.

         (C) In the event, however, that there are not sufficient assets
available to permit payment in full of 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 Junior 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.

         (D) 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 Junior 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 1000 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

                                       7
<PAGE>

shares of Series A Junior Participating Preferred Stock 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.

          Section 8. No Redemption.  The shares of Series A Junior Participating
                     -------------
Preferred Stock shall not be redeemable.

          Section 9. Ranking.  The Series A Junior 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.  At any time when any shares of Series A Junior
                      ---------
Participating Preferred Stock are outstanding, neither the Restated Certificate
of Incorporation of the Corporation nor this Certificate of Amendment shall be
amended in any manner which would materially alter or change the powers,
preferences or special rights of the Series A Junior Participating Preferred
Stock so as to affect them adversely without the affirmative vote of the holders
of 66-2/3% or more of the outstanding shares of Series A Junior Participating
Preferred Stock, voting separately as a class.

          Section 11. Fractional Shares.  Series A Junior 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 Junior Participating Preferred Stock.

                                       8
<PAGE>

          IN WITNESS WHEREOF, we have executed and subscribed this Certificate
and do affirm the foregoing as true under the penalties of perjury this 23rd day
of May, 2001.


                                             By:
                                                --------------------------------
                                                 Name:  Irwin Lerner
                                                 Title:   Chairman of the Board


Attest:



------------------------
Secretary

                                       9
<PAGE>

                                                                       Exhibit B
                                                                       ---------



                           Form of Rights Certificate


Certificate No. R-__________________                 ____________________ Rights


NOT EXERCISABLE AFTER JULY 6, 2011 UNLESS EXTENDED PRIOR THERETO BY THE BOARD OF
DIRECTORS OR EARLIER IF REDEEMED BY THE COMPANY.  THE RIGHTS ARE SUBJECT TO
REDEMPTION, AT THE OPTION OF THE COMPANY, AT $.001 PER RIGHT ON THE TERMS SET
FORTH IN THE RIGHTS AGREEMENT.  UNDER CERTAIN CIRCUMSTANCES, RIGHTS BENEFICIALLY
OWNED BY AN ACQUIRING PERSON (AS SUCH TERM IS 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
AGREEMENT.]*


















_____________________________
*  The portion of the legend in brackets shall be inserted only if applicable
and shall replace the preceding sentence.
<PAGE>

                               Rights Certificate

                                 Medarex, Inc.

          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 May 23, 2001 (the "Rights Agreement"), between Medarex,
Inc. a New Jersey corporation (the "Company"), and Continental Stock Transfer &
Trust Company, a New York corporation (the "Rights Agent"), to purchase from the
Company at any time prior to 5:00 P.M. (Princeton, New Jersey time) on July 6,
2011 (unless such date is extended prior thereto by the Board of Directors) at
the office or offices of the Rights Agent designated for such purpose, or its
successors as Rights Agent, one one-thousandth of a fully paid, non-assessable
share of Series A Junior Participating Preferred Stock (the "Preferred Stock")
of the Company, at a purchase price of one hundred and fifty dollars ($150) per
one one-thousandth of a 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 shares which may be purchased upon
exercise thereof) set forth above, and the Purchase Price per share set forth
above, are the number and Purchase Price as of May 23, 2001, based on the
Preferred Stock as constituted at such date.  The Company reserves the right to
require prior to the occurrence of a Triggering Event (as such term is defined
in the Rights Agreement) that a number of Rights be exercised so that only whole
shares of Preferred Stock will be issued.

          Upon the occurrence of a Section 11(a)(ii) Event (as such term is
defined in the Rights Agreement), if the Rights evidenced by this Rights
Certificate are beneficially owned by (i) an Acquiring Person or an Affiliate or
Associate of any such Acquiring Person (as such terms are defined in the Rights
Agreement), (ii) a transferee of any such Acquiring Person, Associate or
Affiliate, or (iii) under certain circumstances specified in the Rights
Agreement, a transferee of a person who, after such transfer, became an
Acquiring Person, or an Affiliate or Associate of an Acquiring Person, such
Rights shall become null and void and no holder hereof shall have any right with
respect to such Rights from and after the occurrence of such Section 11(a)(ii)
Event.

          As provided in the Rights Agreement, the Purchase Price and the number
and kind of shares of Preferred Stock 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,
including Triggering 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
<PAGE>

in the Rights Agreement. Copies of the Rights Agreement are on file at the
above-mentioned office of the Rights Agent and are also available upon written
request to the Rights Agent.

          This Rights Certificate, with or without other Rights Certificates,
upon surrender at the principal office or offices 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 number of one one-thousandths of a share of Preferred
Stock 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.

          Subject to the provisions of the Rights Agreement, the Rights
evidenced by this Certificate may be redeemed by the Company at its option at a
redemption price of $.001 per Right at any time prior to the earlier of the
close of business on (i) the tenth Business Day following the Stock Acquisition
Date (as such time period may be extended pursuant to the Rights Agreement), and
(ii) the Final Expiration Date.  In addition, under certain circumstances
following the Stock Acquisition Date, the Rights may be exchanged, in whole or
in part, for shares of the Common Stock, or shares of preferred stock of the
Company having essentially the same value or economic rights as such shares.
Immediately upon the action of the Board of Directors of the Company authorizing
any such exchange, and without any further action or any notice, the Rights
(other than Rights which are not subject to such exchange) will terminate and
the Rights will only enable holders to receive the shares issuable upon such
exchange.

          No fractional shares of Preferred Stock will be issued upon the
exercise of any Right or Rights evidenced hereby (other than fractions which are
integral multiples of one one-thousandth of a share of Preferred Stock, which
may, at the election of the Company, be evidenced by depositary receipts), but
in lieu thereof a cash payment will be made, as provided in the Rights
Agreement.

          No holder of this Rights Certificate shall be entitled to vote or
receive dividends or be deemed for any purpose the holder of shares of Preferred
Stock 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 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 consent to or withhold consent from 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.

                                       2
<PAGE>

          WITNESS the facsimile signature of the proper officers of the Company
and its corporate seal.


Dated as of May 23, 2001


ATTEST:                                      MEDAREX, INC.



                                             By:
--------------------------                       ------------------------
          Secretary                          Title:




Countersigned:

CONTINENTAL STOCK TRANSFER & TRUST COMPANY



By:
    --------------------------
Authorized Signature:

                                       3
<PAGE>

                   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: __________________, _____



                                    Signature


Signature Guaranteed:



                                   Certificate
                                   -----------

          The undersigned hereby certifies by checking the appropriate boxes
that:

          (1)  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 Acquiring Person (as such terms are
defined pursuant to 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 an Acquiring Person.
<PAGE>

Dated: __________________, _____



                                    ______________________________
                                    Signature

Signature Guaranteed:


______________________________
<PAGE>

                                     NOTICE
                                     ------


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

                          FORM OF ELECTION TO PURCHASE
                          ----------------------------

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


To: Medarex, Inc.:

      The undersigned hereby irrevocably elects to exercise __________ Rights
represented by this Rights Certificate to purchase the shares of Preferred Stock
issuable upon the exercise of the Rights (or such other securities of the
Company or of any other person which may be issuable upon the exercise of the
Rights) and requests that certificates for such shares be issued in the name of
and delivered to:


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 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:  _______________, _____


                                    Signature


Signature Guaranteed:
<PAGE>

                                  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 Acquiring Person (as such terms are
defined pursuant to 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 became an Acquiring Person or an Affiliate or
Associate of an Acquiring Person.


Dated: ______________, _____



                                  Signature



Signature Guaranteed:
<PAGE>

                                     NOTICE
                                     ------



      The signature to the foregoing Election to Purchase and Certificate must
correspond to the name as written upon the face of this Rights Certificate in
every particular, without alteration or enlargement or any change whatsoever.
<PAGE>

                                                                       Exhibit C
                                                                       ---------


                         SUMMARY OF RIGHTS TO PURCHASE
                                PREFERRED STOCK

          On May 23, 2001, the Board of Directors of Medarex, Inc. (the
"Company") declared a dividend distribution of one Right for each outstanding
share of Company Common Stock to stockholders of record at the close of business
on July 6, 2001 (the "Record Date").  Each Right entitles the registered holder
to purchase from the Company a unit consisting of one one-thousandth of a share
(a "Unit") of Series A Junior Participating Preferred Stock, par value $1 per
share (the "Series A Preferred Stock") at a Purchase Price of one hundred and
fifty ($150) per Unit, subject to adjustment.  The description and terms of the
Rights are set forth in a Rights Agreement (the "Rights Agreement") between the
Company and Continental Stock Transfer & Trust Company, as Rights Agent.

          Initially, the Rights will be attached to all Common Stock
certificates representing shares then outstanding, and no separate Rights
Certificates will be distributed.  Subject to certain exceptions specified in
the Rights Agreement the Rights will separate from the Common Stock and a
Distribution Date will occur upon the earlier of (i) ten (10) business days
following a public announcement that a person or group of affiliated or
associated persons (an "Acquiring Person") has acquired beneficial ownership of
twenty percent (20%) or more of the outstanding shares of Common Stock (the
"Stock Acquisition Date"); or (ii) ten (10) business days (or such later date as
the Board shall determine) following the commencement of a tender offer or
exchange offer that would result in a person or group becoming an Acquiring
Person.  Until the Distribution Date, (i) the Rights will be evidenced by the
Common Stock certificates and will be transferred with and only with such Common
Stock certificates, (ii) new Common Stock certificates issued after the Record
Date will contain a notation incorporating the Rights Agreement by reference and
(iii) the surrender for transfer of any certificates for Common Stock
outstanding will also constitute the transfer of the Rights associated with the
Common Stock represented by such certificate.  Pursuant to the Rights Agreement,
the Company reserves the right to require prior to the occurrence of a
Triggering Event (as defined below) that, upon any exercise of Rights, a number
of Rights be exercised so that only whole shares of Preferred Stock will be
issued.

          The Rights are not exercisable until the Distribution Date and will
expire at 5:00 P.M. (Princeton, New Jersey time) on July 6, 2011, unless such
date is extended or the Rights are earlier redeemed or exchanged by the Company
as described below.

          As soon as practicable after the Distribution Date, Rights
Certificates will be mailed to holders of record of the Common Stock as of the
close of business on the Distribution Date and, thereafter, the separate Rights
Certificates alone will represent the Rights.  Except as otherwise determined by
the Board of Directors, only shares of Common Stock issued prior to the
Distribution Date will be issued with Rights.
<PAGE>

          In the event that a Person becomes an Acquiring Person, except
pursuant to an offer for all outstanding shares of Common Stock which the
independent directors determine to be fair and not inadequate to and to
otherwise be in the best interests of the Company and its stockholders, after
receiving advice from one or more investment banking firms (a "Qualified
Offer"), each holder of a Right will thereafter have the right to receive, upon
exercise, Common Stock (or, in certain circumstances, cash, property or other
securities of the Company) having a value equal to two times the exercise price
of the Right.  Notwithstanding any of the foregoing, following the occurrence of
the event set forth in this paragraph, all Rights that are, or (under certain
circumstances specified in the Rights Agreement) were, beneficially owned by any
Acquiring Person will be null and void.  However, Rights are not exercisable
following the occurrence of the event set forth above until such time as the
Rights are no longer redeemable by the Company as set forth below.

          For example, at an exercise price of  one hundred and fifty ($150) per
Right, each Right not owned by an Acquiring Person (or by certain related
parties) following an event set forth in the preceding paragraph would entitle
its holder to purchase three hundred dollars ($300) worth of Common Stock (or
other consideration, as noted above) for one hundred and fifty ($150).  Assuming
that the Common Stock had a per share value of thirty dollars ($30) at such
time, the holder of each valid Right would be entitled to purchase ten (10)
shares of Common Stock for one hundred and fifty ($150).

          In the event that, at any time following the Stock Acquisition Date,
(i) the Company engages in a merger or other business combination transaction in
which the Company is not the surviving corporation (other than with an entity
which acquired the shares pursuant to a Qualified Offer), (ii) the Company
engages in a merger or other business combination transaction in which the
Company is the surviving corporation and the Common Stock of the Company is
changed or exchanged, or (iii) fifty percent (50%) or more of the Company's
assets, cash flow or earning power is sold or transferred, each holder of a
Right (except Rights which have previously been voided as set forth above) shall
thereafter have the right to receive, upon exercise, common stock of the
acquiring company having a value equal to two times the exercise price of the
Right.  The events set forth in this paragraph and in the second paragraph are
referred to as the "Triggering Events."

          At any time after a person becomes an Acquiring Person and prior to
the acquisition by such person or group of fifty percent (50%) or more of the
outstanding Common Stock, the Board may exchange the Rights (other than Rights
owned by such person or group which have become void), in whole or in part, at
an exchange ratio of one share of Common Stock, or one one-thousandth of a share
of Preferred Stock (or of a share of a class or series of the Company's
preferred stock having equivalent rights, preferences and privileges), per Right
(subject to adjustment).

          At any time until ten business days following the Stock Acquisition
Date, the Company may redeem the Rights in whole, but not in part, at a price of
$.001 per Right (payable in cash, Common Stock or other consideration deemed
appropriate by the

                                       2
<PAGE>

Board of Directors). Immediately upon the action of the Board of Directors
ordering redemption of the Rights, the Rights will terminate and the only right
of the holders of Rights will be to receive the $.001 redemption price.

          Until a Right is exercised, the holder thereof, as such, will have no
rights as a stockholder of the Company, including, without limitation, the right
to vote or to receive dividends.  While the distribution of the Rights will not
be taxable to stockholders or to the Company, stockholders may, depending upon
the circumstances, recognize taxable income in the event that the Rights become
exercisable for Common Stock (or other consideration) of the Company or for
common stock of the acquiring company or in the event of the redemption of the
Rights as set forth above.

          Any of the provisions of the Rights Agreement may be amended by the
Board of Directors of the Company prior to the Distribution Date.  After the
Distribution Date, the provisions of the Rights Agreement may be amended by the
Board in order to cure any ambiguity, to make changes which do not adversely
affect the interests of holders of Rights, or to shorten or lengthen any time
period under the Rights Agreement.  The foregoing notwithstanding, no amendment
may be made at such time as the Rights are not redeemable.

          A copy of the Rights Agreement is being filed with the Securities and
Exchange Commission as an Exhibit to a Registration Statement on Form 8-
A/Current Report on Form 8-K dated May 25, 2001.  A copy of the Rights Agreement
is available free of charge from the Rights Agent.  This summary description of
the Rights does not purport to be complete and is qualified in its entirety by
reference to the Rights Agreement, which is incorporated herein by reference.

                                       3