<PAGE>


                                                                   Exhibit 10.56

July 19, 2001


Dr. George Morstyn
964 Bright Star
Thousand Oaks, CA  91360

Re:    Agreement Regarding Part-Time Special Assignment Position
       ---------------------------------------------------------

Dear George:

On behalf of Amgen Inc. ("Amgen" or the "Company"), I am pleased to confirm in
this letter agreement ("Agreement") the terms and conditions under which you
will continue to be employed by Amgen from and after the date upon which you
cease to serve and resign your positions as Amgen's Senior Vice President of
Development, Chief Medical Officer, and any other officer and/or director
positions that you presently hold with Amgen or any of its subsidiaries or
affiliates, which will occur on January 1, 2002 (the "Effective Date"), it being
acknowledged that you will be on paid vacation from December 1, 2001 until the
Effective Date. You will remain a full-time Amgen staff member and receive all
compensation and benefits of your current position between now and the Effective
Date, although your duties may be modified and your responsibilities may be
reduced by the Company. In addition, it is acknowledged that you will be on a
paid personal leave of absence during all of August 2001 and such leave shall
not reduce any other paid leave or vacation time you are entitled to receive or
use. This Agreement also provides for the termination of your employment with
Amgen on or before July 31, 2004, as set forth below.

1.   POSITION AND DUTIES
     -------------------

     On the Effective Date, you will cease to be a regular full-time employee of
     Amgen, but you will continue to be employed by Amgen as an employee in a
     part-time special assignment position, at grade level 28, with the title of
     Special Advisor, Development reporting to me, or my designee or successor
     (collectively the "Executive VP"). You also will provide assistance to
     Steve Odre, Amgen General Counsel, or his designee or successor
     (collectively the "General Counsel") (the Executive VP and the General
     Counsel, acting individually or together, hereafter are referred to as
     "Your Supervisor"). You will also resign as an officer and/or director of
     Amgen and any Amgen subsidiaries or affiliates on the Effective Date or
     such other time as Amgen may designate in its sole discretion. In
     connection with resigning your offices, you agree to execute and return to
     Amgen with this Agreement two signed, undated original resignation letters
     (the "Resignation Letters") on your Amgen letterhead in the forms provided
     in Appendices A through F to this Agreement. Appendices A through H are
     hereby incorporated into and made part of this Agreement by reference. In
     addition, you agree to take all such further

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 2


     steps as Amgen may deem necessary or appropriate in order to accomplish the
     resignation of any officer and/or director positions that you hold with
     Amgen or any of its subsidiaries or affiliates.

     As Special Advisor, Development you will:

     1. assist the Executive VP by providing technical and professional
     assessments of Amgen's current products and products that Amgen is in the
     process of developing as of the Effective Date; and

     2. assist the General Counsel on intellectual property or other related
     legal matters or litigation including, but not limited to, your meeting
     with Amgen attorneys and testifying or otherwise appearing at depositions
     or court hearings scheduled as a result of any such litigation, including
     preparation for all the above.

     The times and places where this work will be performed will be at your
     choosing unless otherwise requested by Your Supervisor. It is currently
     anticipated that your duties can be performed primarily in Australia except
     that you will be required to make approximately four trips per year to
     Amgen's Thousand Oaks, California facility to perform your duties. You will
     be a member of the Development Department and, as such, Your Supervisor
     will assign these matters to you from time to time and you will provide
     Your Supervisor with quarterly written or oral reports detailing your
     progress toward accomplishing the tasks and directives given to you by Your
     Supervisor. You will also provide additional reports and materials, upon
     reasonable request by Your Supervisor. Your Supervisor will evaluate your
     performance.

     You agree that you will not hire or pay anyone to assist you in performing
     your services under this Agreement. If your work load is such that you
     require assistance, you agree to consult with Your Supervisor, and, if, in
     Amgen's sole discretion, it is deemed appropriate, Amgen either will assign
     one of its then-current employees to assist you, or Amgen will hire an
     assistant for you.

     Your Supervisor will control and direct the manner (including the order),
     in which you perform the services under this Agreement, including the
     details and means by which you provide your services.

     You will be an employee of Amgen for all purposes during the term of this
     Agreement and will not be an independent contractor.

     As we have discussed, the position of Special Advisor, Development, is a
     part-time special assignment position in which you will be required to work
     a minimum of ten (10) hours per month; however, you also agree that, to the
     extent that Your Supervisor requests, you will work up to twenty (20) hours
     per month. In the event that you work more than twenty (20) hours per
     month, then you will receive no additional compensation

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 3

     or benefits for such additional work. If, in any month, Your Supervisor
     does not specifically assign you a sufficient amount of work to meet your
     minimum hour requirement, you will satisfy your minimum requirement by
     independently researching and evaluating product development by competitors
     of Amgen and U.S. Food and Drug Administration developments and reporting
     your findings to Your Supervisor.

     If requested by Your Supervisor, you agree to attend certain meetings or
     programs related to your area of expertise so long as such meeting or
     program does not unreasonably interfere with your other activities.
     Furthermore, from time to time, your duties may require you to travel and
     attend meetings at various locations, including Amgen's Thousand Oaks
     facility, and you agree that no reasonable request by Your Supervisor for
     travel or attendance at meetings will be refused. Your Supervisor will work
     with you in scheduling any such business trips or meetings so that they do
     not unreasonably interfere with your other activities. Amgen will reimburse
     you for your reasonable travel expenses pursuant to the reimbursement
     policy(ies) in place at Amgen at the time you incur such expenses except
     that your air travel for work under this Agreement may be first-class as
     provided by Amgen's travel policy for Amgen officers at the time of such
     travel, even though you will no longer be an Amgen officer.

     You will maintain an accurate and contemporaneous log showing the time you
     have spent performing the foregoing services and this log shall be deemed
     conclusive evidence of the time spent. Your Supervisor, at any time, may
     request a copy of your log and you agree to provide such a copy within a
     reasonable period of time after the request is made.

     We have agreed that your part-time special assignment will continue until
     July 31, 2004, subject to earlier termination by you or Amgen as set forth
     in Paragraph 8 of this Agreement. As long as you are employed by Amgen, you
     will continue to be subject to Amgen's policies and procedures, including
     but not limited to those relating to the non-disclosure of proprietary and
     confidential information and you will continue to be subject to the Amgen
     Inc. Proprietary Information and Inventions Agreement, executed by you on
     or about July 1, 1991 (the "Proprietary Agreement") (which also contains
     obligations that survive the termination of your employment with Amgen).

     During the term of your part-time special assignment, except as set forth
     herein, you may not be employed by any person or company other than Amgen,
     without Amgen's prior approval. You may, however, perform part-time
     services for companies listed on Appendix H to this Agreement, teach, be on
     faculties and sit on boards of directors of other companies outside the
     fields of biotechnology and/or pharmaceutics, or companies within these
     fields having fewer than 500 employees and no current contractual
     relationship with Amgen provided that any such entity (whether profit or
     non-profit) for which you perform services during the term of your
     part-time special assignment with Amgen does not compete with Amgen or
     conduct research and development in any subject area in which Amgen
     competes or conducts research and development at any time during such term
     and provided, further, that your activities do not violate the Proprietary


<PAGE>

Dr. George Morstyn
July 19, 2001
Page 4

     Agreement or interfere or conflict with your duties under this Agreement.
     Your engaging in the activities described in the preceding sentence shall
     not constitute a violation of paragraph 7 of the Proprietary Rights
     Agreement. You agree promptly to notify Amgen in writing if you provide
     services to any third party in the biotechnology or pharmaceutical
     industries during the term of your part-time special assignment. You also
     agree that during the term of this Agreement and for one year after the
     termination of your employment you will not induce any employee of Amgen to
     leave the employ of Amgen or otherwise solicit for employment or
     affiliation, including as an independent contractor, any officer, director,
     or employee of Amgen or its subsidiaries.



2.   COMPENSATION AND BENEFITS
     -------------------------

     Following is a brief description of the compensation and benefits you will
     receive under this Agreement during your part-time special assignment. The
     terms and conditions of all of your benefits are subject to the terms and
     conditions of each of the applicable plans, policies or arrangements, as
     they may be amended or terminated by Amgen from time to time.

     2.1  Compensation: Your compensation will be $32,260.00 per month for the
          ------------
          period from the Effective Date through the Termination Date, as
          defined in Paragraph 8 of this Agreement, subject to applicable income
          tax and employment tax withholding requirements. Amgen will also
          reimburse you for any reasonable business expenses you incur in
          performing your duties, subject to Amgen's standard employee expense
          reimbursement policies.

     2.2  Administrative Support: Amgen will provide you with an office and
          ----------------------
          secretarial assistance for any work that you perform while at Amgen's
          Thousand Oaks headquarters or its Melborne, Australia facility. You
          will also be provided any office equipment and supplies you may need
          to perform your duties under this Agreement and you will have access
          to the services of Amgen's travel department. You may not rent any
          office space or purchase any office equipment in connection with
          performing your services under this Agreement.

     2.3  Management  Incentive Plan: You will not be eligible to participate in
          --------------------------
          Amgen's Management  Incentive Plan ("MIP") for any year after the 2001
          calendar year.

     2.4  Supplemental Retirement Plan: As an employee in a part-time special
          ----------------------------
          assignment position, you will no longer be eligible to receive
          additional credits in your supplemental retirement plan account,
          although you will continue to maintain an account and receive earnings
          on the balance in your account until the termination of your
          employment with Amgen.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 5


     2.5  Retirement and Savings Plan: Pursuant to Section 3.3 of the Amgen
          ---------------------------
          Retirement and Savings Plan (the "401(k) Plan"), employees that are
          eligible to participate in the 401(k) Plan are those that are
          classified as "regular full-time" or "regular part-time" employees. By
          signing below, you expressly acknowledge and agree that Amgen is not
          classifying you as a regular full-time or regular part-time employee
          during your part-time special assignment and, therefore, after the
          Effective Date, you will not be eligible to make contributions or to
          have contributions made on your behalf to the 401(k) Plan. This letter
          qualifies as an agreement pursuant to Section 3.3(c)(2) of the 401(k)
          Plan. You will, however, be able to maintain your account in the
          401(k) Plan to the extent allowed by law.

     2.6  Change of Control Severance Plan: Due to your new grade level, you
          ---------------------------------
          will not be eligible to participate in the Amgen Inc. Change of
          Control Severance Plan on or after the Effective Date.

     2.7  Stock Options:
          -------------

          2.7.1 No New Grants: As an employee in a part-time special assignment
                --------------
                position, you will not be eligible to receive additional stock
                option grants after the Effective Date.

          2.7.2 Vesting During Special Assignment: To the extent that you
                ---------------------------------
                continue in your part-time special assignment, you will be
                eligible to continue to vest in all unvested options that have
                previously been granted to you by Amgen on the dates and in the
                manner provided in your stock option grant agreements and
                applicable stock option plans. No stock options will vest
                following the Termination Date as defined in Paragraph 8 of this
                Agreement.

          2.7.3 Cooperation To Restructure: As we have discussed, it is our
                --------------------------
                intention that your ability to continue to vest in and exercise
                options during your part-time special assignment will not result
                in any additional compensation charges to Amgen in accordance
                with U.S. generally accepted accounting principles. Accordingly,
                at any time that Amgen requests, you agree that you will use
                your reasonable best efforts to cooperate with Amgen to
                restructure this Agreement and the terms of your position, such
                as with respect to hours of employment, reporting relationships,
                working conditions, etc., as Amgen reasonably determines is
                necessary for you to continue to be able to vest and exercise
                your options without creating a compensation charge to Amgen in
                accordance with U.S. generally accepted accounting principles.



<PAGE>

Dr. George Morstyn
July 19, 2001
Page 6


          2.7.4 No Amendment to Stock Option Grant Agreements or Stock Option
                -------------------------------------------------------------
                Plans: Nothing in this Agreement shall be deemed to alter,
                -----
                amend, or otherwise modify the terms of your stock option grant
                agreements or the terms of the applicable stock option plans.

     2.8  Medical, Dental, and Vision Insurance and COBRA: Your medical,
          -----------------------------------------------

          dental and vision insurance coverage will terminate on the Effective
          Date due to your reduction of hours pursuant to this Agreement. If
          after the Effective Date you or your eligible dependents should elect
          to continue coverage under Amgen's group health plan(s) under the
          Consolidated Omnibus Budget Reconciliation Act ("COBRA") continuation
          rights, and you or your eligible dependents timely take the required
          steps to initiate such coverage, then Amgen will pay the cost of COBRA
          coverage for you and your eligible dependents until the earlier of
          June 30, 2003, or until you and/or your eligible dependents no longer
          qualify for COBRA continuation rights or, in the case of your
          dependents, the date on which such dependents cease to be eligible
          dependents under Amgen's group health plan(s), whichever occurs first.
          Such coverage is limited to the insurance benefits provided under
          Amgen's United States medical, dental and vision insurance plans.
          Generally, the period during which you and/or your eligible dependents
          will be eligible for COBRA benefits will be no more than eighteen (18)
          months from the Effective Date. However, if you and/or your eligible
          dependents qualify for COBRA benefits on or after June 30, 2003, then
          you and/or your eligible dependents will have the option of continuing
          coverage under Amgen's group health plan(s), under COBRA and at your
          own expense, for the remainder of the period for which you are
          entitled to receive COBRA benefits, if any, provided that you and your
          eligible dependents continue to meet the qualification requirements
          under COBRA and under Amgen's group health plan(s). For a complete
          description of the rights and responsibilities you and your eligible
          dependents have under COBRA, you must refer to the COBRA documents
          that will be sent to you by Amgen or its designee under separate
          cover. In the event that you work more than twenty (20) hours per week
          during some period(s) of this part-time special assignment, you will
          still be ineligible to participate in Amgen's group health plans as an
          active employee because, despite those periods, you would not be
          considered to "normally" work more than twenty (20) hours per week.
          Therefore, your COBRA continuation period will not terminate merely
          because you work more than twenty (20) hours per week for a temporary
          period during the part-time special assignment. In any event, by
          signing this Agreement, you hereby waive any claim you have to
          benefits under Amgen's group health plans beyond what is provided
          through your COBRA coverage.

          In the event that you and your eligible dependents do not elect COBRA
          coverage, then Amgen will reimburse you for the cost of a private
          medical insurance plan in Australia for you and/or your eligible
          dependents for the duration of this Agreement provided that the
          maximum monthly reimbursement shall be the lesser

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 7


          of (a) the actual cost of to you of such insurance or (b) the amount
          that Amgen would have paid for COBRA coverage per month under the
          preceding paragraph if you had elected COBRA coverage.

     2.9  Basic Life Insurance: Your Basic Life Insurance coverage will
          --------------------
          terminate on the Effective Date. If you are interested in converting
          your insurance to an individual policy, please contact Jean Ellis at
          Aetna (860) 273-7252 within thirty (30) days after the Effective Date.
          In the event that you work more than twenty (20) hours per week during
          some period(s) of this part-time special assignment, you will still be
          ineligible to obtain Basic Life Insurance because, despite those
          periods, you would not be considered to "normally" work more than
          twenty (20) hours per week. In any event, by signing this Agreement,
          you hereby waive your eligibility to obtain Basic Life Insurance
          coverage.

     2.10 Long-Term Disability Plan: Your Long-Term Disability Plan coverage
          -------------------------
          will terminate on the Effective Date and there is no conversion policy
          or plan available for this coverage. In the event that you work more
          than twenty (20) hours per week during some period(s) of this
          part-time special assignment, you will still be ineligible to
          participate in the Long-Term Disability Plan because, despite those
          periods, you would not be considered to "regularly" work more than
          twenty (20) hours per week. In any event, by signing this Agreement,
          you hereby waive your participation in the Long-Term Disability Plan.

     2.11 Amgen Foundation Matching Funds: During the term of your part-time
          -------------------------------
          special assignment, contributions you make to qualified organizations
          will continue to be eligible for matching funds from the Amgen
          Foundation, subject to the same terms, conditions, and limitations
          that apply to contributions made by regular, full time employees of
          Amgen.

     2.12 Employee Stock Purchase Plan: Provided that you take the necessary
          ----------------------------
          steps to enroll in the Employee Stock Purchase Plan (the "ESPP") for
          the purchase period of January 2, 2001, to December 31, 2001, you will
          be eligible to participate in the ESPP for that purchase period.
          Thereafter, however, you will not be eligible to participate in the
          ESPP due to the fact that you will be customarily working less than
          twenty (20) hours per week. In the event that you work more than
          twenty (20) hours per week during some period(s) of this part-time
          special assignment, you will still be ineligible to participate in the
          ESPP after that purchase period because, despite those periods, you
          would not be considered to "customarily" work more than twenty (20)
          hours per week. In any event, by signing this Agreement, you hereby
          waive your eligibility to participate in the ESPP after the purchase
          period of January 2, 2001 to December 31, 2001.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 8




     2.13 Other Benefits: As an employee in a part-time special assignment
          --------------
          position, you will not be eligible to participate in the following
          Amgen benefit plans and programs, as well as any other benefits not
          specifically listed in this letter, after the Effective Date: Medical
          Flexible Spending Account; Dependent Care Assistance Program;
          Accidental Death and Dismemberment Insurance; Voluntary and Dependent
          Life Insurance; use of Amgen Fitness Center facilities; use of Amgen
          Child Care Center facilities; personal illness, vacation/optional
          holiday pay; family illness/personal time; bereavement leave; or
          holidays. Your accrued and unused vacation hours and optional holiday
          pay will be paid to you on the next regularly scheduled payroll date
          following the Effective Date. By signing this Agreement, you agree
          that, notwithstanding any rights you may otherwise have under these
          programs, you hereby waive your claim to any benefits under these
          programs.

3.   TRANSFER OF COMPANY PROPERTY
     ----------------------------

     You promise that on or before the Termination Date, as defined in Paragraph
     8 of this Agreement, you will return to Amgen all files, memoranda,
     documents, records, copies of the foregoing, credit cards, keys, and any
     other Amgen property in your possession or under your control.

4.   OFFICERS AND DIRECTORS INSURANCE
     --------------------------------

     During your part-time special assignment and for four (4) years following
     the Termination Date, as defined in Paragraph 8 of this Agreement, you will
     be covered by such officers and directors insurance coverage that Amgen
     provides to its senior executive officers at your salary grade level 37
     during that time period. In addition, Amgen shall indemnify and hold you
     harmless both during and after the entire term of your employment
     (including your service hereunder) to the fullest extent permitted by law
     with regards to actions or inactions in relation to your duties performed
     at Amgen, both before and after the date of this Agreement. Furthermore,
     you will be entitled to reimbursement of expenses incurred in accordance
     with your rights under California Labor Code Section 2802.

5.   FINANCIAL/TAX CONSULTING REIMBURSEMENT
     --------------------------------------

     Amgen will reimburse you for the legal expenses reasonably incurred by you
     in connection with the review of this Agreement up to a maximum amount of
     $10,000. Amgen will reimburse you for financial and/or tax counseling
     expenses that you reasonably incur, up to a maximum amount of $3,000 per
     year, for each year of this Agreement.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 9




6.   REFERENCE
     ---------

     Amgen will provide you with a positive written factual reference. Kevin W.
     Sharer should be listed as your work reference. You agree to confer with
     Kevin on the form and nature of the reference to be provided to third
     parties concerning the work that you have performed at Amgen. If, by sixty
     (60) days after the Effective Date, you are unable to reach agreement with
     Kevin on the written reference to be provided, then Amgen's only obligation
     will be to respond to inquiries by confirming to third parties the dates of
     your employment at Amgen and the last position you held as an Amgen
     employee.

7.   RELOCATION
     ----------

     If you decide to relocate outside of the (50) mile radius of your residence
     located in Thousand Oaks, California during the period of your part-time
     special assignment or immediately at the termination thereof for any reason
     other than for a Stated Reason, as defined below, then Amgen will pay or
     reimburse you up to the aggregate maximum amount of $50,000 for the
     following relocation assistance: (i) packing, shipping, delivery, storage
     (for up to ninety (90) days) and unpacking of your common household goods
     and furnishings to be arranged by Amgen and handled by Mover's
     International or such other vendor as Amgen may select and paid directly by
     Amgen to Mover's International or such other vendor; (ii) reimbursement
     (not to exceed $9,000) for moving expenses that you have paid to Mover's
     International for moving your goods to Australia; and (iii) payment or
     reimbursement of travel expenses for you and your family to travel to
     Australia. As a condition of receiving this relocation assistance you agree
     to (i) provide all documentation requested by Amgen in connection with this
     Paragraph 7 upon the request of Amgen; (ii) to indemnify and hold Amgen
     harmless for any and all claims in connection with this relocation up to a
     maximum obligation to you of $50,000; and (iii) you agree that Amgen shall
     have no liability to you or your family for lost or damaged items, or
     otherwise, in connection with this relocation. In order to initiate this
     relocation assistance, please contact Christine Swinburne or her designee
     at Amgen.

8.   EARLY TERMINATION OF SPECIAL ASSIGNMENT
     ---------------------------------------

     8.1  At-Will Employment: If you accept this new position, it will become
          ------------------
          your new assignment and you will have no right to return to your
          current position. Although it is currently anticipated that this
          part-time special assignment position will continue until July 31,
          2004, you acknowledge, understand and agree that your employment with
          Amgen remains at-will. Therefore, your employment can terminate, with
          or without cause, and with or without notice, at any time, at your
          option or Amgen's option prior to July 31, 2004. This at-will
          relationship will remain in effect throughout your employment with
          Amgen or any of its subsidiaries or affiliates. The at-will nature of
          your employment, as set forth in this Paragraph, can be modified only
          by a written agreement signed by both me

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 10




          and you which expressly alters it. This at-will relationship may not
          be modified by any oral or implied agreement, or by any Company
          policies, practices or patterns of conduct.

     8.2  Termination by Amgen for a Stated Reason or Termination by You for Any
          ----------------------------------------------------------------------
          Reason Other Than A Covered Breach: If your employment is terminated
          ----------------------------------
          by Amgen for a Stated Reason (as defined below), or if you terminate
          your employment for any reason other than a Covered Breach (as defined
          below), then your payments and benefits from Amgen under this
          Agreement, including but not limited to the vesting of your stock
          options, will cease as of the Termination Date (as defined below).

          For purposes of this Paragraph, a "Stated Reason" means that you:
          breached any material provision of this Agreement or the Proprietary
          Agreement; engaged in fraud or other acts of dishonesty in connection
          with your employment; were guilty of gross misconduct or gross
          negligence; continued to perform your job deficiently after having
          received specific written notice calling your attention to the
          deficiency and requiring improvement; made disparaging remarks about
          Amgen, its products, employees, or research and development abilities
          and projects; or engaged in sexual or any other prohibited form of
          harassment or discrimination.

          For purposes of this Paragraph, a "Covered Breach" means a breach by
          Amgen of its obligations under this Agreement in the following manner
          only: (i) any reduction in your salary or benefits provided for in
          this Agreement, including nonpayment thereof; or (ii) the assignment
          of duties to you that are inconsistent with those set forth in
          Paragraph 1 of this Agreement; or (iii) a reduction in your title or
          position. In order for an event described in the preceding sentence to
          qualify as a Covered Breach, you must give written notice of the event
          to Amgen and Amgen must fail to cure the event within 30 days of
          receipt of that written notice.

     8.3  Termination by Amgen for Other Than a Stated Reason or Termination by
          ---------------------------------------------------------------------
          You for a Covered Breach: In the event your employment is terminated
          ------------------------
          by Amgen or its successor, if any, before July 31, 2004 for any reason
          other than a Stated Reason, or your employment is terminated by you
          for a Covered Breach, then (1) you shall be paid in a cash lump-sum
          all of the remaining payments due to you under this Agreement from the
          date of termination through July 31, 2004 and (2) Amgen shall take the
          necessary corporate action to accelerate the vesting of all of your
          outstanding and then unvested stock options so that they shall vest
          and become immediately exercisable in full as of the Termination Date;
          such stock options, as so accelerated shall be exercisable as provided
          in your stock option grant agreements and applicable stock option
          plans.

<PAGE>
Dr. George Morstyn
July 19, 2001
Page 11




     8.4  Termination Date: The date of the termination of your employment for
          ----------------
          any of the foregoing reasons is referred to in this Agreement as the
          "Termination Date."

9.   DEATH
     -----

     In the event of the termination of your employment hereunder by reason
     of your death prior to July 31, 2004, all of the remaining payments
     that would have been paid to you through July 31, 2004 pursuant to
     Paragraph 2.1 of this Agreement will be payable to the beneficiary or
     beneficiaries that you designate in writing to Amgen. Your other
     remaining benefits will be treated according to their specific terms
     concerning such death. For purposes of Paragraph 10(a) of the Amgen
     Inc. Amended and Restated 1991 Equity Incentive Plan, your employment
     with Amgen shall be deemed to have commenced in 1991, when you first
     became an employee at Amgen.

10.  RELEASE
     -------

     In exchange for consideration provided to you under this Agreement, you
     agree to execute and be bound by the General Release attached hereto as
     Appendix G (the "General Release") and to return the executed
     Agreement, together with the executed General Release and Appendices A
     through H, to me. The General Release is hereby incorporated into and
     made part of the Agreement by this reference.

11.  INTERPRETATION
     --------------

     This Agreement and the Appendices hereto shall be construed as a whole
     according to their fair meaning, and not strictly for or against any of
     the parties. Unless the context indicates otherwise, the term "or"
     shall be deemed to include the term "and" and the singular or plural
     number shall be deemed to include the other. Paragraph headings used in
     this Agreement and the General Release are intended solely for
     convenience of reference and shall not be used in the interpretation of
     any part of this Agreement or the General Release.

12.  NOTICES
     -------

     For the purposes of this Agreement, notices, demands and all other
     communications provided for in this Agreement shall be in writing and
     shall be deemed to have been duly given when delivered either
     personally, by United States certified or registered mail, return
     receipt requested, postage prepaid, or by Australian certified mail -
     requires receipt, postage prepaid, addressed, if to you, to the last
     address on file with Amgen and if to Amgen, to its executive offices or
     to such other address as any party may have furnished to the others in
     writing in accordance herewith, except that notices of change of
     address shall be effective only upon receipt.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 12




13.  ARBITRATION OF DISPUTES
     -----------------------

     13.1     Agreement to Arbitrate: Any dispute (an "Arbitrable Dispute")
              ----------------------
              arising between any of the Amgen Releasees (as defined in
              Paragraph 1.1 of the General Release attached hereto as
              Appendix G) who either consent to arbitration or demand
              arbitration and you, including but not limited to those
              disputes concerning the formation, validity, interpretation,
              effect, or alleged violations of this Agreement or the General
              Release, must be submitted to binding arbitration for
              resolution in Los Angeles, California in accordance with the
              rules and procedures of the Employment Dispute Resolution
              Rules of the American Arbitration Association then in effect.
              The decision of the arbitrator shall be final and binding on
              the parties, and any court of competent jurisdiction may enter
              judgment upon the award. Except for an action taken outside of
              arbitration pursuant to Subparagraph 13.4 of this Agreement,
              should any party pursue any other legal or administrative
              action outside of arbitration against the other, the
              responding party shall be entitled to the return of any
              payments that party made under this Agreement and shall be
              entitled to recover all costs, expenses and attorneys' fees
              the responding party incurs as a result of such action. The
              arbitrator may not modify or change this Agreement in any way.

     13.2     Costs of Arbitration: Each party shall pay the fees of their
              --------------------
              respective attorneys, the expenses of their witnesses and any
              other expenses connected with the arbitration, but all other
              costs of the arbitration, including the fees of the
              arbitrator, cost of any record or transcript of the
              arbitration, administrative fees and other fees and costs
              shall be paid by Amgen, except that you shall pay an amount
              equal to 50% of the filing fee for a civil action in the court
              of general jurisdiction where the claim arose. Subject to the
              arbitrator's discretion, the party losing the arbitration
              shall reimburse the party who prevailed for all fees and
              expenses the prevailing party paid pursuant to the preceding
              sentence, and (where a prevailing party attorney's fees
              provision exists) shall also reimburse the prevailing party
              for attorney's fees paid.

     13.3     Exclusive Remedy: Arbitration in this manner shall be the
              ----------------
              exclusive remedy for any Arbitrable Dispute. The arbitrator's
              decision or award shall be fully enforceable and subject to an
              entry of judgment by a court of competent jurisdiction. Except
              for an action taken outside of arbitration pursuant to
              Subparagraph 13.4 of this Agreement, should you or any of the
              Releasees (as defined in Paragraph 1.1 of the General Release
              attached hereto as Appendix G) who either consent to
              arbitration or demand arbitration, without the consent of the
              other party, attempt to resolve an Arbitrable Dispute by any
              method other than arbitration pursuant to this Paragraph 13,
              the responding party shall be entitled to recover from the
              initiating party all damages, expenses and attorneys' fees
              incurred as a result.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 13




      13.4     Sole Exception: Notwithstanding the foregoing, a dispute
               --------------
               relating to alleged violation(s) of Paragraph 2 and/or
               Paragraph 3 of the General Release attached hereto as Exhibit
               G, including those involving the disclosure of the existence,
               terms or amount of this Agreement, and/or the use or
               disclosure of information which is prohibited by the
               Proprietary Agreement, and/or the criticism, denigration or
               disparagement of Amgen, any other Releasee (as defined in
               Paragraph 1.1 of the General Release attached hereto as
               Appendix G), or any of Amgen's products, processes,
               experiments, policies, practices, standards of business
               conduct, or areas or techniques of research may be resolved
               through a means other than arbitration.

14.   CHOICE OF LAWS
      --------------

      This Agreement shall be governed by, and shall be construed and
      enforced in accordance with, the substantive laws of the State of
      California, without regard to principles of conflicts of laws, as
      applied to contracts entered into and to be performed entirely within
      such state by residents thereof.

15.   TAXES
      -----

      You acknowledge and agree that all payments made pursuant to this
      Agreement shall be made less applicable tax withholdings and/or other
      withholdings as required by law. You acknowledge and agree that you,
      and not Amgen, shall be solely responsible for any taxes (other than
      Amgen's share of FICA) imposed upon you as a result of entering into
      this Agreement.

16.   MITIGATION
      ----------

      You shall not be required to mitigate amounts payable under this
      Agreement by seeking other employment or otherwise, and there shall be
      no offset against amounts due you under this Agreement on account of
      employment after the termination of your part-time special assignment.
      Additionally, amounts owed to you under this Agreement shall not be
      offset by any claims Amgen may have against you and Amgen's obligation
      to make the payments provided for in this Agreement and otherwise to
      perform its obligations hereunder, shall not be affected by any other
      circumstances, including, without limitation, any counterclaim,
      recoupment, defense or other right which Amgen may have against you or
      others.

17.   NO ASSIGNMENT OR DELEGATION
      ---------------------------

      Amgen has selected you for this part-time special assignment because it
      has judged that your unique experience and skills are those Amgen
      required for the job. Accordingly, you may not assign or delegate any
      of your duties or responsibilities under this Agreement.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 14




18.  NATURE, EFFECT AND INTERRELATION OF THIS AGREEMENT
     --------------------------------------------------

     18.1     Amgen's Successors: No rights or obligations of Amgen under this
              ------------------
              Agreement may be assigned or transferred except that Amgen will
              require any successor (whether direct or indirect, by purchase,
              merger, consolidation or otherwise) to all or substantially all
              of the business and/or assets of Amgen to expressly assume and
              agree to perform this Agreement in the same manner and to the same
              extent that Amgen would be required to perform it if no such
              succession had taken place. As used in this Agreement, "Amgen"
              shall mean Amgen as herein before defined and any successor to its
              business and/or assets (by merger, purchase or otherwise) which
              executes and delivers the agreement provided for in this Paragraph
              18 or which otherwise becomes bound by all the terms and
              provisions of this Agreement by operation of law.

     18.2     Your Successors: No rights or obligations of you under this
              ---------------
              Agreement may be assigned or transferred by you, other than your
              rights to payments or benefits hereunder, which may be
              transferred only by will or the laws of descent and
              distribution. Upon your death, this Agreement and all rights
              of you hereunder shall inure to the benefit of and be
              enforceable by your beneficiary or beneficiaries, personal or
              legal representatives, or estate, to the extent any such
              person succeeds to your interests under this Agreement. You
              shall be entitled to select and change a beneficiary or
              beneficiaries to receive any benefit or compensation payable
              hereunder following your death by giving Amgen written notice
              thereof. In the event of your death or a judicial
              determination of your incompetence, reference in this
              Agreement to you shall be deemed, where appropriate, to refer
              to your beneficiary(ies), estate or other legal
              representative(s). If your should die following your
              Termination Date while any amounts would still be payable to
              you hereunder if you had continued to live, all such amounts
              unless otherwise provided herein shall be paid in accordance
              with the terms of this Agreement to such person or persons so
              appointed in writing by you, or otherwise to your legal
              representatives or estate.

     18.3     Implementation: Amgen and you both agree that, without the
              --------------
              receipt of further consideration, they will sign and deliver
              any documents and do anything else that is necessary in the
              future to make the provisions of this Agreement effective.

<PAGE>

Dr. George Morstyn
July 19, 2001
Page 15




19. ENTIRE AGREEMENT
    ----------------

    The Proprietary Agreement, your stock option agreements, this Agreement, and
    Appendices A through H to this Agreement constitute the entire agreement,
    arrangement and understanding between you and Amgen; they may not be
    modified or canceled in any manner except by a writing signed by both you
    and Amgen. This Agreement supersedes any prior or contemporaneous agreement,
    arrangement or understanding on this subject matter. By executing this
    Agreement as provided below, you expressly acknowledge the termination of
    any such prior agreement, arrangement or understanding. Also, by executing
    this Agreement, you affirm that no one has made any written or verbal
    statement that contradicts the provisions of this Agreement.

Sincerely yours,



/s/ Roger M. Perlmutter
-----------------------
Roger M. Perlmutter

Executive Vice President Research and Development
Amgen Inc.

Acknowledged and Agreed:



/s/ George Morstyn                                   Dated:   7/19/01
------------------------------------                         ----------
Dr. George Morstyn

<PAGE>

                                   APPENDIX A

<PAGE>

                                   RESIGNATION
                                   -----------

     The undersigned hereby resigns his position as Senior Vice President,
Development and Chief Medical Officer of Amgen Inc., effective _____________

Date: _______________


                                                   /s/ George Morstyn
                                                   ------------------
                                                   George Morstyn

<PAGE>

                                   APPENDIX B

<PAGE>

TO:      AMGEN-REGENERON PARTNERS (the "Partnership")

AND TO:  The Joint Management Committee of the Partnership






                                   RESIGNATION
                                   -----------


         The undersigned hereby resigns as an Amgen member of the Joint
Management Committee effective _______________.


Date:
       -------

                                 /s/ George Morstyn
                                 ------------------
                                 George Morstyn

<PAGE>

                                   APPENDIX C

<PAGE>

TO:      AMGEN AUSTRALIA PTY LIMITED (the "Company")

AND TO:  The Directors and Shareholders of the Company






                                   RESIGNATION
                                   -----------


         The undersigned hereby resigns as Secretary of the Company effective
_______________


Date:
       -------

                                 /s/ George Morstyn
                                 ------------------
                                 George Morstyn

<PAGE>

                                   APPENDIX D

<PAGE>

TO:      AMGEN CANADA INC. (the "Company")

AND TO:  The Directors and Shareholders of the Company






                                   RESIGNATION
                                   -----------



         The undersigned hereby resigns as Senior Vice President, Development
and Chief Medical Officer of the Company effective _______________.


Date:
       -------

                                 /s/ George Morstyn
                                 ------------------
                                 George Morstyn

<PAGE>

                                   APPENDIX E

<PAGE>

                                                                   _______, 200_

To the Directors of
Amgen Limited (the "Company")
Carmelite
50 Victoria Embankment
Blackfriars
London EC4Y ODX

Dear Sirs:

I hereby resign as a director of the Company to be effective as of _________,
200_ and confirm that I have no claims against the Company whatsoever.


EXECUTED as a deed                  )
by GEORGE MORSTYN                   )
in the presence of:                 )



                                 /s/ George Morstyn
                                 ------------------
                                 George Morstyn



Signature of Witness:


/s/ Shae Williams
------------------------------

Name:          Shae Williams

Address:       One Amgen Center Drive
               Thousand Oaks, CA 91320

Occupation:    Administrative Coordinator V

<PAGE>

                                   APPENDIX F

<PAGE>

TO:      KIRIN-AMGEN, INC. (the "Company")

AND TO:  The Directors and Shareholders of the Company




                                   RESIGNATION
                                   -----------


         The undersigned hereby resigns as an Amgen Director of the Company
effective ______________.

Date:
       -------

                                 /s/ George Morstyn
                                 ---------------------------
                                 George Morstyn

<PAGE>

                                   APPENDIX G

                                 GENERAL RELEASE

     By signing below, Amgen Inc. ("Amgen" or the "Company") and you, George
Morstyn, agree to all of the terms and conditions set forth in this General
Release, which resolves all issues between you and the Company including, but
not limited to, those related to your employment with the Company, and the
termination thereof.

1.   COMPLETE RELEASE
     ----------------

     1.1  Release: In exchange for consideration provided to you and the Company
          -------
          under the Agreement, the receipt of which and adequacy thereof you and
          the Company hereby acknowledge, you irrevocably and unconditionally
          release all the claims described in Subparagraph 1.2 of this General
          Release that you may have against the following persons or entities
          (the "Amgen Releasees"): Amgen, all related or affiliated companies
          and all of Amgen's or such related or affiliated companies'
          predecessors, successors, and assigns; and, with respect to each such
          entity, all of its past and present employees, officers, directors,
          stockholders, owners, representatives, assigns, attorneys, agents,
          insurers, employee benefit programs (and the trustees, administrators,
          fiduciaries and insurers of such programs) and any other persons
          acting by, through, under or in concert with any of the persons or
          entities listed in this Subparagraph and each of them; and the Company
          irrevocably and unconditionally releases all the claims described in
          Subparagraph 1.2 of this General Release that the Company may have
          against the following persons or entities (the "Mortsyn Releasees")
          you, your employees, agents, attorneys, representatives, successors,
          and assigns, past and present and each of them.

     1.2  Claims Released: Except as provided in Subparagraph 1.4 of this
          ---------------
          General Release, the claims released include all claims, promises,
          debts, causes of action or similar rights of any type or nature you
          have or had against the Amgen Releasees and/or the Company has or had
          against the Morstyn Releasees, including but not limited to those
          which in any way relate to: (a) your employment with Amgen, the change
          in your employment status or the termination of your employment as of
          the Termination Date, such as claims for compensation, bonuses,
          commissions, lost wages or unused accrued vacation, or sick pay; (b)
          the design or administration of any employee benefit program or your
          entitlement to benefits under any such program; (c) any rights you may
          have to severance or similar benefits under any program, policy or
          procedure of Amgen; (d) any rights you may have to the continued
          receipt of health or life insurance-type benefits, except for any
          rights you may have to continue benefits pursuant to COBRA at your own
          expense; (e) any claims to attorneys fees or

<PAGE>

         other indemnities; and (f) any other claims or demands you or the
         Company may have on any basis. The claims released, for example,
         may have arisen under any of the following statutes or common law
         doctrines:

         1.2.1 Anti-Discrimination Statutes, such as Title VII of the Civil
               ----------------------------
               Rights Act of 1964, (S)1981 of the Civil Rights Act of 1866 and
               Executive Order 11246, which prohibit discrimination based on
               race, color, national origin, religion or sex; the Equal Pay Act,
               which prohibits paying men and women unequal pay for equal work;
               the Americans With Disabilities Act and (S)503 and (S)504 of the
               Rehabilitation Act of 1973, which prohibit discrimination against
               the disabled; the California Fair Employment and Housing Act,
               which prohibits discrimination in employment based on race,
               color, national origin, ancestry, physical or mental disability,
               medical condition, marital status, sexual orientation, sex or
               age.

         1.2.2 Federal Employment Statutes, such as the WARN Act, which
               ---------------------------
               requires that advance notice be given of certain work force
               reductions; Employee Retirement Income Security Act of 1974,
               which, among other things, protects pension or health plan
               benefits; and the Fair Labor Standards Act of 1938, which
               regulates wage and hour matters.

         1.2.3 Other Laws, such as any federal, state or local laws providing
               ----------
               workers' compensation benefits; restricting an employer's right
               to terminate employees or otherwise regulating employment; or
               enforcing express or implied employment contracts or requiring an
               employer to deal with employees fairly or in good faith;
               California Labor Code(S)(S)200 et seq., relating to salary,
                                              -- ---
               commission, compensation, benefits and other matters; the
               California Workers' Compensation Act; the California Unemployment
               Insurance Code; any applicable California Industrial Welfare
               Commission Order; and any other federal, state or local laws,
               whether based on statute, regulation or common law, providing
               recourse for alleged wrongful discharge, physical or personal
               injury, emotional distress, fraud, negligent misrepresentation,
               libel, slander, defamation and similar or related claims.

         1.2.4 Age Discrimination In Employment Act
               ------------------------------------

               1.2.4.1 You also acknowledge and agree that by signing the
                       Agreement and this General Release, in addition to the
                       any matters discussed above, you are waiving and
                       releasing and all claims, charges, or rights you may have
                       under the Age Discrimination In Employment Act of 1967,
                       as amended ("ADEA"), that this waiver and release is
                       knowing and voluntary, and that the consideration given
                       for this waiver and release is in addition to anything of
                       value to which you were already entitled as an employee
                       of Amgen. You further acknowledge that you have been
                       advised that: (a) you should consult with an attorney (at

<PAGE>




                       your own expense) prior to executing the Agreement, and
                       this General Release (you understand that whether you
                       consult an attorney or not is your decision); (b) you
                       have at least twenty-one (21) days in which to consider
                       the Agreement and this General Release (although you
                       may choose to execute the Agreement and this General
                       Release earlier); (c) the Agreement and this General
                       Release does not waive or release any rights or claims
                       you may have under the ADEA which may arise after you
                       execute the Agreement and this General Release; (d) you
                       have seven (7) days following execution of the
                       Agreement and this General Release to revoke your
                       consent to the Agreement and this General Release (to
                       be effective, any revocation must be actually received
                       in writing by me by 5:30 p.m. on the seventh day); and
                       (e) the Agreement and this General Release shall not be
                       effective until the seven (7) day revocation period has
                       expired.

                       In the event that you exercise this right to revoke this
                       General Release, you and Amgen agree that the Agreement
                       (including without limitation the Resignation Letters
                       attached to the Agreement as Appendices A-F) will be
                       simultaneously revoked.

               1.2.4.2 You acknowledge and agree that you were first given
                       a copy of the Agreement and this General Release on
                       January 16, 2001 that you have been given the
                       opportunity to consult with whomever you wish regarding
                       the Agreement and this General Release and that you
                       have entered into the Agreement and this General
                       Release voluntarily and with full knowledge of their
                       final and binding effect.

     1.3  Release Extends to Both Known and Unknown Claims: This General Release
          ------------------------------------------------
          covers both claims that you and/or Amgen know about and those you
          and/or Amgen do not know about. You understand the significance of
          this release of unknown claims and this waiver of statutory protection
          against a release of unknown claims by you. You expressly waive all
          rights afforded by any statute which limits the effect of a release
          with respect to unknown claims. You and Amgen expressly waive the
          protection of (S) 1542 of the Civil Code of the State of California,
          which states as follows:

               "A general release does not extend to claims which the creditor
                does not know or suspect to exist in his favor at the time
                of executing the release, which if known by him must have
                materially affected his settlement with the debtor."

<PAGE>

     1.4  Claims Not Released: This General Release does not release your right
          -------------------
          or the Company's right to enforce the Agreement, nor does it release
          your rights under Labor Code (S) 2802 or the Company's rights under
          the Amgen Inc. Proprietary Information and Inventions Agreement
          executed by you on or about July 1, 1991 (the "Proprietary
          Agreement").

     1.5  Ownership of Claims: You represent that you have not assigned or
          -------------------
          transferred, or purported to assign or transfer, all or any part of
          any claim released by the Agreement and this General Release.

2.   YOUR PROMISES In addition to the release of claims provided for in
     -------------
     Paragraph 1 of this General Release, you also agree to the following:

     2.1  Employee's Representations:
          --------------------------

          2.1.1 You represent and warrant that you are changing the scope of
                your responsibilities voluntarily and that your age has not been
                a factor in any employment decision involving you.

          2.1.2 You represent and warrant that you have not been the victim of
                age or other discrimination or wrongful treatment in connection
                with your employment with Amgen.

          2.1.3 You represent and warrant that you have not breached any portion
                of the Proprietary Agreement.

          2.1.4 You represent and warrant that you have not suffered any
                job-related injury to which you might be entitled to
                compensation or relief, such as an injury for which you might
                receive a workers' compensation award now or in the future.

          2.1.5 You represent and warrant that you are not aware of any facts
                that would (a) establish, (b) tend to establish, or (c) in any
                way support an allegation of, a violation by the Company of the
                federal False Claims Act (or any similar state or federal qui
                                                                          ---
                tam statute).
                ---

     2.2  No Future Employment: You understand that, as provided in Paragraph 7
          --------------------
          of the Agreement, your employment with Amgen and all related or
          affiliated companies will terminate forever on the Termination Date
          and you promise never to seek employment with Amgen or its related or
          affiliated companies in the future. If your employment is not
          terminated by Amgen for a Stated Reason, Amgen shall treat this
          termination as a resignation on its records. You acknowledge and agree
          that the Agreement, together with this General Release, contemplates
          your termination from Amgen on the Termination Date, and that the
          release in Paragraph 1 of this General Release shall cover your entire
          employment with Amgen and the termination of that employment.

<PAGE>

     2.3  You are Not to Harm Amgen: You agree not to criticize, denigrate or
          -------------------------
          otherwise disparage Amgen, any other Releasee, or any of Amgen's
          products, processes, experiments, policies, practices, standards of
          business conduct, or areas or techniques of research; provided,
          however, that nothing in this General Release shall prohibit you from
          complying with any lawful subpoena or court order.

     2.4  No Pursuit of Released Claims: You promise never to file or prosecute
          -----------------------------
          a lawsuit or other complaint or charge asserting any claims that are
          released by the Agreement. You represent that you have not filed or
          caused to be filed any lawsuit, complaint or charge with respect to
          any claim the Agreement and this General Release.

     2.5  Agreement to be Kept Confidential: You agree not to disclose the
          ---------------------------------
          terms, amount or existence of the Agreement and this General Release
          to anyone other than (i) Your Supervisor; (ii) members of your
          immediate family; or (iii) your professional representatives and, even
          as to such persons in groups (ii) and (iii), only if they are informed
          of and agree to honor this confidentiality requirement. Such persons'
          violation of this confidentiality requirement shall be treated as a
          violation of the Agreement and this General Release by you. This
          Subparagraph shall not prohibit disclosure of the terms, amount or
          existence of the Agreement and this General Release to the extent (i)
          such information has been made public by Amgen in a proxy statement or
          other corporate disclosure; (ii) legally necessary to enforce the
          Agreement and this General Release or (iii) to the extent otherwise
          legally required. Since the damages Amgen would suffer if this
          Subparagraph were violated would be difficult to calculate, you
          promise to pay Amgen $7,500 for each violation and, in addition, Amgen
          shall be entitled to the relief described in Paragraph 3.

3.   CONSEQUENCES OF YOUR VIOLATION OF YOUR PROMISES
     -----------------------------------------------

     3.1  General Consequences: If you break any of the promises made in the
          --------------------
          Agreement or this General Release, for example, by filing or
          prosecuting a lawsuit based on claims that you have released, or if
          any representation made by you in this General Release was false when
          made, or if you have, as of the Effective Date, breached any portion
          of the Proprietary Agreement, or if you, at any time after the
          Effective Date, breach any portion of the Proprietary Agreement that
          contains obligations which survive the termination of your employment
          with the Company, you (a) shall forfeit all right to future benefits
          under the Agreement; (b) must repay all benefits previously received,
          other than the monthly compensation paid to you under Paragraph 2.1 of
          the Agreement, upon Amgen's demand; and (c) must pay reasonable
          attorneys' fees and all other costs incurred as a result of your
          breach or false representation, such as the cost of defending any suit
          brought with respect to a released claim by you or other owner of a
          released claim.

<PAGE>
          In addition, in order to ensure that you have complied fully with your
          obligations under Paragraph 2.1.5 of this General Release, you hereby
          covenant and agree that to the full extent permitted by law, you
          hereby waive and release any and all rights or claims you may have to
          any proceeds or awards that you may be entitled to under any qui tam
                                                                       --- ---
          proceeding brought against Amgen. You further agree that you shall
          deliver any such money, proceeds, or awards to the U.S. government.

     3.2  Injunctive Relief: You further agree that Amgen would be irreparably
          -----------------
          harmed by any actual or threatened violation of Paragraph 2.5 that
          involves disclosure of the existence, terms or amount of the Agreement
          and this General Release, and/or the use or disclosure of information
          that is prohibited by the Proprietary Agreement (which contains
          obligations that survive the termination of your employment with
          Amgen), and that Amgen shall be entitled to an injunction prohibiting
          you from committing any such violation.

     3.3  Challenges to Validity: Should you attempt to challenge the formation
          ----------------------
          or enforceability of the Agreement, this General Release, and/or the
          Proprietary Agreement, you shall initially tender, by certified check
          delivered to Amgen, all amounts received pursuant to the Agreement,
          other than the monthly compensation paid to you under Paragraph 2.1 of
          the Agreement, plus interest at the legal rate and invite Amgen to
          cancel the Agreement. In the event Amgen accepts this offer, the
          Agreement shall be canceled. In the event Amgen does not accept this
          offer, Amgen shall so notify you and the amount tendered by you shall
          be placed in an interest-bearing account pending a determination of
          the enforceability of the Agreement, this General Release, and/or the
          Proprietary Agreement. If the Agreement, General Release and/or
          Proprietary Agreement is determined to be enforceable, the amount in
          the account shall be repaid to you; if the Agreement, General Release
          and/or Proprietary Agreement is determined not to be enforceable, the
          amount in the account shall be retained by Amgen or its designee.

4.   VOLUNTARILY ENTERING AGREEMENT
     ------------------------------

     You acknowledge that you (a) have had a sufficient period to consider and
     review the Agreement and this General Release before signing them; (b) have
     carefully read the Agreement and this General Release; and (c) fully
     understand the Agreement and this General Release and are entering into
     them voluntarily.

5.   SEVERABILITY
     ------------

     The provisions of the Agreement and this General Release are severable. If
     any one or more of the provisions contained therein, or the application
     thereof in any circumstance, is held invalid, illegal or unenforceable in
     any respect and for any reason, the validity, legality and enforceability
     of any such provision in every other respect and of the remaining
     provisions hereof shall not be affected or impaired in any way, it being
     intended that all of the parties'

<PAGE>

     rights and privileges arising hereunder shall be enforceable to the fullest
     extent permitted by law.

6.   NON-ADMISSION OF LIABILITY
     --------------------------

     Amgen has entered into the Agreement and this General Release with you to
     effect a mutually acceptable resolution of each claim that is released in
     Paragraph 1. Amgen does not believe or admit that it or any other Releasee
     has done anything wrong. You agree that neither the Agreement nor this
     General Release is admissible in any court or other forum for any purpose
     other than the enforcement of their terms.

7.   ENCOURAGEMENT TO CONSULT WITH ATTORNEY
     --------------------------------------

     You acknowledge that Amgen strongly encouraged you to discuss the Agreement
     and this General Release with an attorney (at your own expense, except as
     provided in Paragraph 5 of the Agreement) before signing the Agreement and
     this General Release and that, to the extent you deemed it appropriate, you
     did so.

PLEASE READ THIS GENERAL RELEASE CAREFULLY.  IT CONTAINS A RELEASE OF ALL KNOWN
AND UNKNOWN CLAIMS.


Executed at Thousand Oaks, California this 19 day of July, 2001.
            -------------                  --


/s/ George Morstyn
------------------
George Morstyn


Executed at Thousand Oaks, California this 19th day of July, 2001.


/s/ Roger M. Perlmutter
-----------------------
Amgen Inc.
By:  Roger M. Perlmutter
Executive Vice President Research and Development

<PAGE>

                                   APPENDIX H

                Bionomics Limited (based in Adelaide, Australia)
                   CSL Limited (based in Melbourne, Australia)
           The Scientific Advisory Board of Baxter International Inc.
                         (based in Deerfield, Illinois)