<PAGE>

                                                                    EXHIBIT 10.1
                          SHAREHOLDER VOTING AGREEMENT



                                  BY AND AMONG

                                   AMGEN INC.

                       AMERICAN HOME PRODUCTS CORPORATION,

                             MDP HOLDINGS, INC. and

                            LEDERLE PARENTERALS, INC.



                          Dated as of December 16, 2001

12/16/2001


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                          SHAREHOLDER VOTING AGREEMENT

     This SHAREHOLDER VOTING AGREEMENT (this "Agreement") is entered into as of
                                              ---------
December 16, 2001, by and among Amgen Inc., a Delaware corporation ("Parent"),
                                                                     ------
American Home Products Corporation, a Delaware corporation ("AHP"), MDP
                                                             ---
Holdings, Inc., a Delaware corporation and wholly-owned subsidiary of AHP ("Sub
1"), and Lederle Parenterals, Inc., a New Jersey corporation and wholly-owned
subsidiary of AHP ("Sub 2" and, together with AHP and Sub 1, the
"Shareholders").
 ------------

                              W I T N E S S E T H:

     WHEREAS, as of the date hereof, each Shareholder "beneficially owns" (as
such term is defined in Rule 13d-3 promulgated under the Securities Exchange Act
of 1934, as amended) and is entitled to dispose of (or to direct the disposition
of) and to vote (or to direct the voting of) the number of shares of common
stock, par value $0.01 per share (the "Common Stock"), of Immunex Corporation, a
                                       ------------
Washington corporation (the "Company"), set forth opposite such Shareholder's
                             -------
name on Schedule I hereto (such shares of Common Stock, together with any other
shares of Common Stock the voting power over which is acquired by any
Shareholder during the period from and including the date hereof through and
including the date on which this Agreement is terminated in accordance with its
terms, are collectively referred to herein as the "Subject Shares");
                                                   --------------

     WHEREAS, Parent, AMS Acquisition Inc., a Washington corporation and a
wholly-owned subsidiary of Parent ("Merger Sub"), and the Company propose to
                                    ----------
enter into an Agreement and Plan of Merger, dated as of the date hereof (the
"Merger Agreement"), pursuant to which Merger Sub will merge with and into the
 ----------------
Company, with the Company surviving as a wholly-owned subsidiary of Parent (the
"Merger"); and
 ------

     WHEREAS, as a condition to the willingness of Parent to enter into the
Merger Agreement, and as an inducement and in consideration therefor, each
Shareholder is executing this Agreement.

     NOW, THEREFORE, in consideration of the foregoing and the mutual premises,
representations, warranties, covenants and agreements contained herein, the
parties hereto, intending to be legally bound, hereby agree as follows:

                                   ARTICLE I
                                  DEFINITIONS

     Section 1.1 Capitalized Terms. For purposes of this Agreement, capitalized
terms used and not defined herein shall have the respective meanings ascribed to
them in the Merger Agreement.

     Section 1.2 Other Definitions. For purposes of this Agreement:

     (a) "Affiliate" means, with respect to any specified Person, any Person
that directly, or indirectly through one or more intermediaries, controls, or is
controlled by, or is under common control with, the Person specified. For
purposes of this Agreement, with respect to

<PAGE>

each Shareholder, the term "Affiliate" shall not include the Company and the
Persons that directly, or indirectly through one or more intermediaries, are
controlled by the Company.

     (b) "Governance Agreement" means the Amended and Restated Governance
Agreement by and among the Company, American Cyanamid Company and Lederle
Oncology Corporation, dated as of December 15, 1992, as amended.

     (c) "Person" means an individual, corporation, limited liability company,
partnership, association, trust, unincorporated organization, other entity or
group.

     (d) "Representative" means, with respect to any particular Person, any
director, officer, employee, accountant, consultant, legal counsel, investment
banker, advisor, agent or other representatives of such Person.

                                   ARTICLE II
                     VOTING AGREEMENT AND IRREVOCABLE PROXY

     Section 2.1 Agreement to Vote the Subject Shares. Each Shareholder, in its
capacity as such, hereby agrees that, during the period commencing on the date
hereof and continuing until the termination of this Agreement (such period, the
"Voting Period"), at any meeting (or any adjournment or postponement thereof) of
 -------------
the Company's shareholders, however called, or in connection with any written
consent of the Company's shareholders, such Shareholder shall vote (or cause to
be voted) its Subject Shares (x) in favor of the approval of the terms of the
Merger Agreement, the Merger and the other transactions contemplated by the
Merger Agreement (and any actions required in furtherance thereof), (y) against
any action, proposal, transaction or agreement that would result in a breach in
any respect of any covenant, representation or warranty or any other obligation
or agreement of the Company contained in the Merger Agreement or of any
Shareholder contained in this Agreement, and (z) except with the written consent
of Parent, against the following actions or proposals (other than the
transactions contemplated by the Merger Agreement): (i) any Acquisition
Proposal; and (ii) (A) any change in the persons who constitute the board of
directors of the Company that is not approved in advance by at least a majority
of the persons who were directors of the Company as of the date of this
Agreement (or their successors who were so approved); (B) any material change in
the present capitalization of the Company or any amendment of the Company's
articles of incorporation or bylaws; (C) any other material change in the
Company's corporate structure or business; or (D) any other action or proposal
involving the Company or any of its subsidiaries that is intended, or could
reasonably be expected, to prevent, impede, interfere with, delay, postpone or
adversely affect the transactions contemplated by the Merger Agreement;
provided, however, that nothing in this Agreement shall limit or affect any
actions taken by any member of the board of directors of the Company nominated
by, or appointed at the request of, AHP solely in his or her capacity as a
director of the Company; provided, further, that nothing in this Agreement shall
be interpreted as obligating the Shareholders to exercise any options to acquire
shares of Common Stock. Any such vote shall be cast or consent shall be given in
accordance with such procedures relating thereto so as to ensure that it is duly
counted for purposes of determining that a quorum is present and for purposes of
recording the results of such vote or consent. Each Shareholder agrees not to
enter into any agreement or commitment with any

                                       2

<PAGE>

Person the effect of which would be inconsistent with or violative of the
provisions and agreements contained in this Article II.

     Section 2.2 Grant of Irrevocable Proxy. Each Shareholder hereby appoints
Parent and any designee of Parent, and each of them individually, as such
Shareholder's proxy and attorney-in-fact, with full power of substitution and
resubstitution, to vote or act by written consent during the Voting Period with
respect the Subject Shares in accordance with Section 2.1. This proxy is given
to secure the performance of the duties of each Shareholder under this
Agreement. The Shareholders shall promptly cause a copy of this Agreement to be
deposited with the Company at its principal place of business. Each Shareholder
shall take such further action or execute such other instruments as may be
necessary to effectuate the intent of this proxy.

     Section 2.3 Nature of Irrevocable Proxy. The proxy and power of attorney
granted pursuant to Section 2.2 by each Shareholder shall be irrevocable during
the term of this Agreement, shall be deemed to be coupled with an interest
sufficient in law to support an irrevocable proxy and shall revoke any and all
prior proxies granted by such Shareholder. The power of attorney granted by each
Shareholder herein is a durable power of attorney and shall survive the
dissolution, bankruptcy, death or incapacity of such Shareholder. The proxy and
power of attorney granted hereunder shall terminate upon the termination of this
Agreement.

                                  ARTICLE III
                                   COVENANTS

     Section 3.1 Generally.

     (a) Except for pledges in existence as of the date hereof, each Shareholder
agrees that during the Voting Period, except as contemplated by the terms of
this Agreement, it shall not (i) sell, transfer, tender, pledge, encumber,
assign or otherwise dispose of (collectively, a "Transfer"), or enter into any
contract, option or other agreement with respect to, or consent to, a Transfer
of, any or all of the Subject Shares; provided, however, that any Shareholder
                                      --------  -------
may Transfer any or all of its Subject Shares to any other Shareholder or to any
wholly owned subsidiary of AHP that agrees in writing to be bound by the terms
of this Agreement and, with the consent of Parent (which consent shall not be
unreasonably withheld), may pledge or encumber any Subject Shares so long as
such pledge or encumbrance would not impair any Shareholder's ability to perform
its obligations under this Agreement; or (ii) take any action that would have
the effect of preventing, impeding, interfering with or adversely affecting its
ability to perform its obligations under this Agreement.

     (b) In the event of a stock dividend or distribution, or any change in the
Common Stock by reason of any stock dividend or distribution, split-up,
recapitalization, combination, exchange of shares or the like, the term "Subject
Shares" shall be deemed to refer to and include the Subject Shares as well as
all such stock dividends and distributions and any securities into which or for
which any or all of the Subject Shares may be changed or exchanged or which are
received in such transaction.

                                       3

<PAGE>

     (c) AHP agrees that it shall not, and it shall cause its controlled
Affiliates not to, (i) directly or indirectly, acquire additional shares of
Common Stock (including through the exercise of subscription rights as set forth
in Section 2.01 of the Governance Agreement or quarterly purchase rights as set
forth in Section 2.02 of the Governance Agreement) or (ii) exercise any of the
registration rights set forth in Article VI of the Governance Agreement.

     Section 3.2 Standstill Obligations of Shareholders. Each Shareholder,
jointly and severally, covenants and agrees with Parent that, during the Voting
Period:

     (a) Such Shareholder shall not, nor shall such Shareholder permit any
controlled Affiliate of such Shareholder to, nor shall such Shareholder act in
concert with or permit any controlled Affiliate to act in concert with any
Person to make, or in any manner participate in, directly or indirectly, a
"solicitation" of "proxies" (as such terms are used in the rules of the
Securities and Exchange Commission) or powers of attorney or similar rights to
vote, or seek to advise or influence any Person with respect to the voting of,
any shares of Common Stock in connection with any vote or other action on any
matter, other than to recommend that shareholders of the Company vote in favor
of the Merger and the Merger Agreement and otherwise as expressly provided by
Article II of this Agreement.

     (b) Such Shareholder shall not, nor shall such Shareholder permit any
controlled Affiliate of such Shareholder to, nor shall such Shareholder act in
concert with or permit any controlled Affiliate to act in concert with any
Person to, deposit any shares of Common Stock in a voting trust or subject any
shares of Common Stock to any arrangement or agreement with any Person with
respect to the voting of such shares of Common Stock, except as provided by
Article II of this Agreement.

     (c) Such Shareholder shall not, and shall direct its Representatives not
to, directly or indirectly, through any officer, director, agent or otherwise,
enter into, solicit, initiate, conduct or continue any discussions or
negotiations with, or knowingly encourage or respond to any inquiries or
proposals by, or provide any information to, any Person, other than Parent,
relating to any Acquisition Proposal; provided, however, that, in connection
with Acquisition Proposals as to which Parent has received a Superior Proposal
Notice, AHP may provide information and engage in discussions to the same extent
as the Company is so permitted pursuant to Section 6.4(c) of the Merger
Agreement. Each Shareholder hereby represents that it is not now engaged in
discussions or negotiations with any party other than Parent with respect to any
Acquisition Proposal. Promptly after receipt of any Acquisition Proposal or any
request for nonpublic information or inquiry which it reasonably believes could
lead to an Acquisition Proposal, AHP shall provide Parent with written notice of
the material terms and conditions of such Acquisition Proposal, request or
inquiry, and the identity of the person or group making any such Acquisition
Proposal, request or inquiry, and a copy of all written materials provided in
connection with such Acquisition Proposal, request or inquiry. After receipt of
the Acquisition Proposal, request or inquiry, AHP shall promptly keep Parent
informed in all material respects of the status and details (including material
amendments or proposed material amendments) of any such Acquisition Proposal,
request or inquiry.

                                       4

<PAGE>

     (d) Notwithstanding any of the provisions of this Agreement, AHP has two
representatives on the Company's Board of Directors and such persons will act in
their capacities as directors of the Company in accordance with their fiduciary
duties to the Company and its shareholders.

     Section 3.3 Further Agreements of Parent. Parent hereby covenants and
agrees with the Shareholders that it shall take all reasonably necessary actions
to ensure that immediately following the Effective Time, each Shareholder or its
designee shall receive the Cash Consideration in immediately available funds
with respect to such number of Subject Shares for which such Shareholder is
entitled to receive pursuant to the terms of the Merger Agreement; provided,
that such Shareholder or its designee shall have surrendered to Parent a
Certificate or Certificates evidencing such number of Subject Shares together
with a letter or letters of transmittal in accordance with Section 2.2 of the
Merger Agreement, duly executed and completed in accordance with the
instructions thereto. The remainder of the Merger Consideration that the
Shareholders would be entitled to under the Merger Agreement would be
distributed following the Effective Time in the manner set forth in the Merger
Agreement.

                                   ARTICLE IV
               REPRESENTATIONS AND WARRANTIES OF EACH SHAREHOLDER

         Each Shareholder hereby represents and warrants, jointly and severally,
to Parent as follows:

     Section 4.1 Due Organization, etc. Each Shareholder is a company duly
organized and validly existing under the laws of the jurisdiction of its
incorporation. Each Shareholder has all necessary corporate power and authority
to execute and deliver this Agreement and to consummate the transactions
contemplated hereby. The execution and delivery of this Agreement and the
consummation of the transactions contemplated hereby by each Shareholder have
been duly authorized by all necessary action on the part of such Shareholder.

     Section 4.2 Ownership of Shares. Schedule I sets forth, opposite each
Shareholder's name, the number of shares of Common Stock over which such
Shareholder has record and beneficial ownership as of the date hereof. As of the
date hereof, each Shareholder is the lawful owner of the shares of Common Stock
denoted as being owned by such Shareholder on Schedule I and has the sole power
to vote (or cause to be voted) such shares of Common Stock. Except as set forth
on such Schedule I and as provided in the Governance Agreement, no Shareholder
nor any Affiliate of a Shareholder owns or holds any right to acquire any
additional shares of any class of capital stock of the Company or other
securities of the Company or any interest therein or any voting rights with
respect to any securities of the Company. Each Shareholder has good and valid
title to the Common Stock denoted as being owned by such Shareholder on Schedule
I, free and clear of any and all pledges, mortgages, liens, charges, proxies,
voting agreements, encumbrances, adverse claims, options, security interests and
demands of any nature or kind whatsoever, other than those created by this
Agreement or provided in the Governance Agreement or as could not reasonably be
expected to impair any Shareholder's ability to perform its obligations under
this Agreement.

                                       5

<PAGE>

     Section 4.3 No Conflicts. (i) No filing with any governmental authority,
and no authorization, consent or approval of any other Person is necessary for
the execution of this Agreement by any Shareholder and the consummation by any
Shareholder of the transactions contemplated hereby and (ii) none of the
execution and delivery of this Agreement by the Shareholders, the consummation
by any Shareholder of the transactions contemplated hereby or compliance by any
Shareholder with any of the provisions hereof shall (A) conflict with or result
in any breach of the organizational documents of any Shareholder, (B) result in,
or give rise to, a violation or breach of or a default under any of the terms of
any material contract, understanding, agreement or other instrument or
obligation to which any Shareholder is a party or by which any Shareholder or
any of its Subject Shares or assets may be bound, or (C) violate any applicable
order, writ, injunction, decree, judgment, statute, rule or regulation, except
for any of the foregoing as could not reasonably be expected to impair any
Shareholder's ability to perform its obligations under this Agreement.

     Section 4.4 Reliance by Parent. Each Shareholder understands and
acknowledges that Parent is entering into the Merger Agreement in reliance upon
the execution and delivery of this Agreement by such Shareholder.

                                   ARTICLE V
                    REPRESENTATIONS AND WARRANTIES OF PARENT

     Parent hereby represents and warrants to the Shareholders as follows:

     Section 5.1 Due Organization, etc. Parent is a company duly organized and
validly existing under the laws of the jurisdiction of its incorporation. Parent
has all necessary corporate power and authority to execute and deliver this
Agreement and to consummate the transactions contemplated hereby. The execution
and delivery of this Agreement and the consummation of the transactions
contemplated hereby by Parent have been duly authorized by all necessary action
on the part of Parent.

     Section 5.2 Conflicts. (i) No filing with any governmental authority, and
no authorization, consent or approval of any other Person is necessary for the
execution of this Agreement by Parent and the consummation by Parent of the
transactions contemplated hereby and (ii) none of the execution and delivery of
this Agreement by Parent, the consummation by Parent of the transactions
contemplated hereby shall (A) conflict with or result in any breach of the
organizational documents of Parent, (B) result in, or give rise to, a violation
or breach of or a default under any of the terms of any material contract,
understanding, agreement or other instrument or obligation to which Parent is a
party or by which Parent or any of its assets may be bound, or (C) violate any
applicable order, writ, injunction, decree, judgment, statute, rule or
regulation, except for any of the foregoing as could not reasonably be expected
to impair Parent's ability to perform its obligations under this Agreement.

     Section 5.3 Reliance by the Shareholders. Parent understands and
acknowledges that the Shareholders are entering into this Agreement in reliance
upon the execution and delivery of the Merger Agreement by Parent.

                                       6

<PAGE>

                                   ARTICLE VI
                                   TERMINATION

     Section 6.1 Termination. This Agreement shall terminate, and none of Parent
or any Shareholder shall have any rights or obligations hereunder and this
Agreement shall become null and void and have no effect upon the earliest to
occur of (i) the mutual consent of Parent and AHP, (ii) the Effective Time,
(iii) the date of termination of the Merger Agreement in accordance with its
terms, (iv) the date of any modification, waiver or amendment to the Merger
Agreement in a manner that reduces either the Exchange Ratio or the Cash
Consideration, and (v) December 31, 2002; provided, however, that termination of
                                          --------  -------
this Agreement shall not prevent any party hereunder from seeking any remedies
(at law or in equity) against any other party hereto for such party's breach of
any of the terms of this Agreement. Notwithstanding the foregoing, Section 7.1
and Sections 7.5 through 7.18, inclusive, of this Agreement shall survive the
termination of this Agreement.

                                  ARTICLE VII
                                 MISCELLANEOUS

     Section 7.1 Appraisal Rights. To the extent permitted by applicable law,
each Shareholder hereby waives any rights of appraisal or rights to dissent from
the Merger that it may have under applicable law.

     Section 7.2 Publication. Each Shareholder hereby permits Parent to publish
and disclose in the Proxy Statement/Prospectus (including all documents and
schedules filed with the Securities and Exchange Commission) its identity and
ownership of shares of Common Stock and the nature of its commitments,
arrangements and understandings pursuant to this Agreement; provided, however,
that such publication and disclosure is subject in all cases to the prior review
and comment by AHP and its advisors.

     Section 7.3 HSR Requirements. Each Shareholder agrees promptly to make all
necessary filings, if any, and thereafter make any other required submissions,
if any, with respect to the Merger Agreement, the AHP Agreements (as that term
is defined in the Merger Agreement), the Merger and the transactions
contemplated by the Merger Agreement required under the Hart-Scott-Rodino
Antitrust Improvements Act of 1976, as amended, any antitrust and competition
laws of any other applicable jurisdiction and any other applicable law. Each
Shareholder shall cooperate with Parent in connection with the making of any
such filings referenced in the preceding sentence, including providing copies of
all such documents to Parent and its advisors prior to filing and, if requested,
to accept all reasonable additions, deletions or changes suggested in connection
therewith.

     Section 7.4 Affiliate Letters. Each Shareholder agrees to execute an
affiliate agreement, as soon as practicable after the date hereof, in
substantially the form attached hereto as Exhibit 7.4.

     Section 7.5 Further Actions. Each of the parties hereto agrees that it will
use its reasonable best efforts to do all things necessary to effectuate this
Agreement.

     Section 7.6 Fees and Expenses. Except as provided below, each of the
parties shall be responsible for its own fees and expenses (including, without
limitation, the fees and expenses of financial consultants, investment bankers,
accountants and counsel) (collectively, "Fees") in connection with the entering
into of this Agreement and the consummation of the transactions

                                       7

<PAGE>

contemplated hereby and by the Merger Agreement. In the event that the Merger
Agreement is terminated (i) pursuant to Section 8.1(a) or Section 8.1(h)(ii) of
the Merger Agreement, or (ii) by the Company pursuant to Section 8.1(e) or
Section 8.1(g) of the Merger Agreement, then Parent shall promptly reimburse AHP
for all of the Fees of the Shareholders incurred in connection with the
transactions contemplated hereby and by the Merger Agreement; provided, however,
that Parent's liability for Fees payable to AHP pursuant to this Section 7.6
shall in no event exceed $3 million.

     Section 7.7 Amendments, Waivers, etc. This Agreement may not be amended,
changed, supplemented, waived or otherwise modified, except upon the execution
and delivery of a written agreement executed by each of the parties hereto. The
failure of any party hereto to exercise any right, power or remedy provided
under this Agreement or otherwise available in respect hereof at law or in
equity, or to insist upon compliance by any other party hereto with its
obligations hereunder, and any custom or practice of the parties at variance
with the terms hereof shall not constitute a waiver by such party of its right
to exercise any such or other right, power or remedy or to demand such
compliance.

     Section 7.8 Specific Performance. The parties hereto agree that irreparable
damage would occur in the event any of the provisions of this Agreement were not
to be performed in accordance with the terms hereof and that the parties shall
be entitled to specific performance of the terms hereof in addition to any other
remedies at law or in equity.

     Section 7.9 Notices. Any notices or other communications required or
permitted under, or otherwise in connection with this Agreement shall be in
writing and shall be deemed to have been duly given when delivered in person or
upon confirmation of receipt when transmitted by facsimile transmission (with
confirmation) or on receipt after dispatch by registered or certified mail,
postage prepaid, addressed, or on the next Business Day if transmitted by
national overnight courier, in each case as follows:

     If to Parent or Merger Sub, addressed to it at:

            Amgen Inc.
            One Amgen Center Drive
            Thousand Oaks, California 91320-1799
            Fax:  (805) 449-3540
            Attn: Chief Executive Officer

     with a copy to:

            Latham & Watkins
            885 Third Avenue, Suite 1000
            New York, NY  10022-4802
            Fax:  (212) 751-4864
            Attn: Charles Nathan

            and

                                       8

<PAGE>

            Latham & Watkins
            633 West Fifth Street, Suite 4000
            Los Angeles, CA  90071-2007
            Fax:  (213) 891-8763
            Attn: Gary Olson
                  Paul D. Tosetti
                  Charles Ruck

     If to any Shareholder, addressed to:

            American Home Products Corporation
            Five Giralda Farms
            Madison, NJ 07940
            Fax:  (973) 660-7156
            Attn: Louis L. Hoynes, Esq.

            with a copy to:

            Simpson Thacher & Bartlett
            425 Lexington Avenue
            New York, NY  10017
            Fax:  (212) 455-2502
            Attn: Charles I. Cogut

     Section 7.10 Headings. The headings contained in this Agreement are for
reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement.

     Section 7.11 Severability. If any term or other provision of this Agreement
is invalid, illegal or incapable of being enforced by any rule of Law or public
policy, all other conditions and provisions of this Agreement shall nevertheless
remain in full force and effect so long as the economic or legal substance of
the transactions contemplated hereby is not affected in any manner materially
adverse to any party. Upon such determination that any term or other provision
is invalid, illegal or incapable of being enforced, the parties hereto shall
negotiate in good faith to modify this Agreement so as to effect the original
intent of the parties as closely as possible in an acceptable manner to the end
that transactions contemplated hereby are fulfilled to the extent possible.

     Section 7.12 Entire Agreement. This Agreement (together with the Merger
Agreement, to the extent referred to herein) constitutes the entire agreement of
the parties and supersedes all prior agreements and undertakings, both written
and oral, between the parties, or any of them, with respect to the subject
matter hereof.

     Section 7.13 Assignment. This Agreement shall not be assigned by operation
of law or otherwise without the prior written consent of each of the parties,
except that each of Parent and Merger Sub may assign and transfer its rights and
obligations hereunder to any direct or indirect wholly subsidiary of Parent.

                                       9

<PAGE>

     Section 7.14 Parties in Interest. This Agreement shall be binding upon and
inure solely to the benefit of each party hereto and their respective successors
and assigns, and nothing in this Agreement, express or implied, is intended to
or shall confer upon any other Person any right, benefit or remedy of any nature
whatsoever under or by reason of this Agreement.

     Section 7.15 Mutual Drafting. Each party hereto has participated in the
drafting of this Agreement, which each party acknowledges is the result of
extensive negotiations between the parties.

     Section 7.16 Governing Law; Consent to Jurisdiction; Waiver of Trial by
Jury.

     (a) This Agreement and the transactions contemplated hereby, and all
disputes between the parties under or related to the Agreement or the facts and
circumstances leading to its execution, whether in contract, tort or otherwise,
shall be governed by and construed in accordance with the laws of the State of
Delaware, without regard to the application of Delaware principles of conflicts
of laws.

     (b) Each of the parties hereto hereby irrevocably and unconditionally
submits, for itself and its property, to the exclusive jurisdiction of any
Delaware State court, or Federal court of the United States of America, sitting
in Delaware, and any appellate court from any thereof, in any action or
proceeding arising out of or relating to this Agreement or the agreements
delivered in connection herewith or the transactions contemplated hereby or
thereby or for recognition or enforcement of any judgment relating thereto, and
each of the parties hereby irrevocably and unconditionally (i) agrees not to
commence any such action or proceeding except in such courts, (ii) agrees that
any claim in respect of any such action or proceeding may be heard and
determined in such Delaware State court or, to the extent permitted by law, in
such Federal court, (iii) waives, to the fullest extent it may legally and
effectively do so, any objection which it may now or hereafter have to the
laying of venue of any such action or proceeding in any such Delaware State or
Federal court, and (iv) waives, to the fullest extent permitted by law, the
defense of an inconvenient forum to the maintenance of such action or proceeding
in any such Delaware State or Federal court. Each of the parties hereto agrees
that a final judgment in any such action or proceeding shall be conclusive and
may be enforced in other jurisdictions by suit on the judgment or in any other
manner provided by law. Each party to this Agreement irrevocably consents to
service of process in the manner provided for notices in Section 7.9. Nothing in
this Agreement shall affect the right of any party to this Agreement to serve
process in any other manner permitted by law.

     (c) EACH PARTY ACKNOWLEDGES AND AGREES THAT ANY CONTROVERSY WHICH MAY ARISE
UNDER THIS AGREEMENT IS LIKELY TO INVOLVE COMPLICATED AND DIFFICULT ISSUES, AND
THEREFORE IT HEREBY IRREVOCABLY AND UNCONDITIONALLY WAIVES ANY RIGHT IT MAY HAVE
TO A TRIAL BY JURY IN RESPECT OF ANY LITIGATION DIRECTLY OR INDIRECTLY ARISING
OUT OF OR RELATING TO THIS AGREEMENT AND ANY OF THE AGREEMENTS DELIVERED IN
CONNECTION HEREWITH OR THE TRANSACTIONS CONTEMPLATED HEREBY OR THEREBY. EACH
PARTY CERTIFIES AND ACKNOWLEDGES THAT (I) NO REPRESENTATIVE, AGENT OR ATTORNEY
OF ANY

                                       10

<PAGE>

OTHER PARTY HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT SUCH OTHER PARTY WOULD
NOT, IN THE EVENT OF LITIGATION, SEEK TO ENFORCE EITHER OF SUCH WAIVERS, (II) IT
UNDERSTANDS AND HAS CONSIDERED THE IMPLICATIONS OF SUCH WAIVERS, (III) IT MAKES
SUCH WAIVERS VOLUNTARILY, AND (IV) IT HAS BEEN INDUCED TO ENTER INTO THIS
AGREEMENT BY, AMONG OTHER THINGS, THE MUTUAL WAIVERS AND CERTIFICATIONS IN THIS
SECTION 7.16(c).

     Section 7.17 Counterparts. This Agreement may be executed in counterparts,
each of which when executed shall be deemed to be an original but all of which
taken together shall constitute one and the same agreement.

     Section 7.18 Acknowledgement. The parties hereto acknowledge and agree that
this Agreement is entered into pursuant to the provisions of Section 23B.07.310
of the Business Corporation Act of the State of Washington.

                                    * * * * *


                                       11

<PAGE>

     IN WITNESS WHEREOF, Parent and each Shareholder have caused this Agreement
to be duly executed as of the day and year first above written.

                                         AMGEN INC.
                                         a Delaware corporation

                                         By: /s/ Kevin W. Sharer
                                            ------------------------------------
                                            Name:  Kevin W. Sharer
                                            Title: Chairman of the Board, CEO
                                                   and President


                                         AMERICAN HOME PRODUCTS CORPORATION
                                         a Delaware corporation

                                         By: /s/ Kenneth Martin
                                            ------------------------------------
                                            Name:
                                            Title:


                                         MDP HOLDINGS, INC.
                                         a Delaware corporation

                                         By: /s/ Kenneth Martin
                                            ------------------------------------
                                            Name:
                                            Title:


                                         LEDERLE PARENTERALS, INC.
                                         a New Jersey corporation

                                         By: /s/ Kenneth Martin
                                            ------------------------------------
                                            Name:
                                            Title:


<PAGE>

                                   Schedule I
                                   ----------

                            Ownership of Common Stock
                            -------------------------

           Name and Address of Shareholder                    Number of Shares
           -------------------------------                    ----------------
American Home Products Corporation(1)                                0
Five Giralda Farms
Madison, NJ 07940

MDP Holdings, Inc.                                              180,153,032
Five Giralda Farms
Madison, NJ 07940

Lederle Parenterals, Inc.                                        43,225,056
Five Giralda Farms
Madison, NJ 07940
________________

(1)  American Home Products Corporation beneficially owns the shares held by MDP
     Holdings, Inc. and Lederle Parenterals, Inc.