<PAGE>

                                                                    EXHIBIT 10.2

                                    GUARANTEE

     GUARANTEE dated as of March 2, 2001 (this "Guarantee") made by IMMUNEX
                                                ---------
CORPORATION, a Washington corporation ("Immunex") and IMMUNEX MANUFACTURING
                                        -------
CORPORATION, a Washington corporation (together with Immunex, individually and
collectively, the "Guarantor"), in favor of Immunex Real Estate Trust 2001 (the
                   ---------
"Lessor"), Immunex Funding Corp., a Delaware corporation ("SPC"), the Investors,
 ------                                                    ---
and Chase Manhattan Bank, as Administrative Agent for SPC (the Lessor, the
Investors, SPC, Chase Manhattan Bank, as Administrative Agent for SPC, and their
respective successors and assigns, collectively known as the "Beneficiaries").
                                                              -------------

                             Preliminary Statement
                             ---------------------

     Pursuant to the SPC Loan Agreement, SPC has agreed to make loans (the "SPC
                                                                            ---
Loans") to the Lessor upon the terms and conditions set forth therein, to be
-----
evidenced by notes issued by the Lessor under the SPC Loan Agreement. The Lessor
has entered into the SPC Loan Agreement for the purpose of facilitating the
financing, with the proceeds of the SPC Loans, of the acquisition of a leasehold
interest in the Land and the construction of Improvements thereon, which Land
and Improvements shall, in turn, be leased to the Lessee.

     The SPC Loans will be made from time to time at the request of the
Construction Agent in consideration for the agreement of the Construction Agent,
for the benefit of the Lessor, to perform its obligations under the Agency
Agreement. It is a condition precedent to the obligation of SPC to make its SPC
Loans to the Lessor under the SPC Loan Agreement and for the Investors to make
their Contributions under the Participation Agreement that the Guarantor shall
have executed and delivered this Guarantee for the ratable benefit of the
Beneficiaries.

     The Guarantor wishes to induce (i) SPC to make the SPC Loans and enter into
the SPC Loan Agreement and the other Operative Agreements to which it is a party
and (ii) the Investors to make the Investor Contributions and enter into the
Participation Agreement (referred to below) and the other Operative Agreements
to which they are party.

     NOW, THEREFORE, in consideration of the premises contained herein and to
induce (i) SPC to make the SPC Loans and enter into the SPC Loan Agreement and
the other Operative Agreements to which it is a party and (ii) the Investors to
make the Investor Contributions and enter into the Participation Agreement and
the other Operative Agreements to which they are a party, the Guarantor hereby
agrees for the ratable benefit of the Beneficiaries as follows:
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     1. Defined Terms. (a) Capitalized terms not otherwise defined herein shall
        -------------
have the meanings set forth on Annex A to the Participation Agreement dated as
of the date hereof among Immunex, Immunex Funding Corp., as SPC, The Chase
Manhattan Bank, as Administrative Agent, as Collateral Agent and as Agent Bank,
Immunex Real Estate Trust 2001, the Investors party thereto, the Banks party
thereto, and Wilmington Trust Company.

     (b) As used herein, the following terms shall have the following meanings:

          "Contribution Obligations" means the collective reference to the
           ------------------------
outstanding amount of the Investor Contributions and the Investor Yield with
respect thereto and all rights of the Investors to receive distributions under
the Trust Agreement and any of the other Operative Agreements.

          "Guaranteed Obligations" means the collective reference to (i) the
           ----------------------
Note Obligations and (ii) the Contribution Obligations and, with respect to each
such obligation, interest accruing thereon at the applicable rate provided in
the Operative Agreements after maturity and interest accruing at the then
applicable rate provided in the Operative Agreements after the filing of any
petition in bankruptcy, or the commencement of an insolvency, reorganization or
like proceeding, whether or not a claim for post-filing or post-petition
interest is allowed in such proceeding and whether such obligations are direct
or indirect, absolute or contingent, due or to become due, or now existing or
hereinafter incurred, which may arise, under, out of or in connection with any
of the Operative Agreements, any other document made, delivered or given in
connection therewith, in each case whether on account of principal, interest,
Investor Contributions or Investor Yield, reimbursement obligations, fees,
indemnities, costs, expenses, or payment obligations (including, without
limitation, all fees and disbursements of counsel to any of the Beneficiaries).

          "Note Obligations" means the collective reference to the unpaid
           ----------------
principal of and interest on the SPC Loans and the SPC Notes and all other
payment obligations and liabilities of the Lessor to the Administrative Agent
and SPC under the SPC Notes, the SPC Loan Agreement and any of the other
Operative Agreements.

     2.  Guarantee. (a) Subject to the provisions of paragraph 2(b) and (c), the
         ---------
Guarantor hereby unconditionally and irrevocably guarantees to the Beneficiaries
and their respective successors, endorsees, transferees and assigns the prompt
and complete payment when due (whether at the stated maturity, by acceleration
or otherwise) of the Guaranteed Obligations.

     (b) Anything to the contrary notwithstanding, (i) if (A) a Construction
Risk Event has occurred, (B) no other Lease Event of Default has occurred and is
continuing at such time, and (C) the Construction Agent performs its obligations
under Section 5.4(a) of the Agency Agreement, then the obligations of the
Guarantor hereunder shall be limited to the Guaranteed Obligations in the amount
of the Non-Completion Amount and all other amounts owing by Lessee or
Construction Agent under Section 5.4(a) of the Agency Agreement, and (ii)(A) if
no Lease Event of Default, or on the Maturity Date, no Lease Default has
occurred and is continuing, the obligations of the Guarantor hereunder shall be
limited to the unpaid principal of and interest on the Tranche A SPC Notes and
(B) if any (x) Lease Event of Default or (y) on the

                                       2
<PAGE>

Maturity Date, any Lease Default has occurred and is continuing, the Guarantor
shall be liable for the Guaranteed Obligations.

     (c) Without affecting any of the Construction Agent's obligations under
Section 5.4(a) of the Agency Agreement and the Guarantor's obligations hereunder
with respect thereto, anything else herein to the contrary notwithstanding,
during the Construction Period the Lessee shall not be liable for any Note
Obligations hereunder.

     (d) The Guarantor further agrees to pay any and all expenses (including,
without limitation, fees and disbursements of counsel) which may be paid or
incurred by the Administrative Agent, Collateral Agent or any Beneficiary in
enforcing, or obtaining advice of counsel in respect of, any rights with respect
to, or collecting, any or all of the Guaranteed Obligations and/or enforcing any
rights with respect to, or collecting against, the Guarantor under this
Guarantee. This Guarantee shall remain in full force and effect until the
Guaranteed Obligations and all amounts owing hereunder are paid in full,
notwithstanding that from time to time prior thereto the Lessor may be free from
any Guaranteed Obligations.

     (e) The Guarantor agrees that the Guaranteed Obligations may at any time
and from time to time exceed the amount of the liability of the Guarantor
hereunder without impairing this Guarantee or affecting the rights and remedies
of Collateral Agent or any Beneficiary hereunder with respect to the amount of
the liability of Guarantor.

     (f) No payment or payments made by the Lessor, any Guarantor or any other
Person or received or collected by Collateral Agent or any Beneficiary from the
Lessor, a Guarantor or any other Person by virtue of any action or proceeding or
any set-off or appropriation or application at any time or from time to time in
reduction of or in payment of the Guaranteed Obligations shall be deemed to
modify, reduce, release or otherwise affect the liability of the Guarantor
hereunder which shall, notwithstanding any such payment or payments remain
liable for the Guaranteed Obligations up to the maximum liability of such
Guarantor as set forth in this Section 2 until the Guaranteed Obligations and
all amounts owing hereunder are paid in full.

     (g) The Guarantor agrees that whenever, at any time, or from time to time,
it shall make any payment to anything in this Guarantee (including this Section
2) or in any other Operative Agreement to the contrary notwithstanding, any
payment made by the Lessee, Construction Agent or the Guarantor to the Lessor in
accordance with the Operative Agreements shall satisfy and discharge the
obligations of the Guarantor hereunder to the extent of such payment; and
Guarantor shall have no obligation or liability to the Collateral Agent or any
Beneficiary on account of its liability hereunder, it will notify Collateral
Agent in writing that such payment is made under this Guarantee for such
purpose.

     (h) The obligations of each entity comprising Guarantor hereunder shall be
joint and several.

     3. Right of Set-off. In addition to any rights now or hereafter granted
        ----------------
under applicable law or otherwise, and to the extent not prohibited by
applicable law, and not by way of limitation of any such rights, upon the
occurrence and during the continuance of an Event of

                                       3
<PAGE>

Default, Collateral Agent and each Beneficiary is hereby authorized at any time
or from time to time, without presentment, demand, protest or other notice of
any kind to the Lessor, the Guarantor or to any other Person, any such notice
being hereby expressly waived, to set off and to appropriate and apply any and
all deposits (general or special) and any other Indebtedness at any time held or
owing by Collateral Agent or such Beneficiary (including, without limitation, by
branches and agencies of Collateral Agent or such Beneficiary wherever located)
to or for the credit or the account of the Guarantor against and on account of
the obligations and liabilities of the Guarantor hereunder (subject to the
limitations herein), and all other claims of any nature or description arising
out of or connected with this Guarantee or any other Operative Agreement,
provided that all notices and cure periods have been provided to Lessor as
required under the applicable Operative Agreement(s), but irrespective of
whether Collateral Agent or such Beneficiary shall have made any demand
hereunder and although said obligations, liabilities or claims, or any of them,
shall be contingent or unmatured. Collateral Agent and each Beneficiary agrees
promptly to notify Guarantor after any such set off and application made by
Collateral Agent or such Beneficiary; provided that failure to give such notice
shall not affect the validity of such set-off and application.

           4. No Subrogation. Notwithstanding any payment or payments made by
              --------------
the Guarantor hereunder or any set-off or application of funds of the Guarantor
by any Beneficiary, the Guarantor shall not be entitled to exercise or enforce
any subrogation rights of Collateral Agent or any Beneficiary against the Lessor
or any other Person or any collateral security or guarantee or right of offset
held by Collateral Agent or any Beneficiary for the payment of the Guaranteed
Obligations, nor shall the Guarantor seek or be entitled to seek any
contribution or reimbursement from the Lessor or any other Person in respect of
payments made by the Guarantor hereunder, until all amounts owing to Collateral
Agent and the Beneficiaries by the Lessor on account of the Guaranteed
Obligations and all amounts owing hereunder are paid in full. If any amount
shall be paid to the Guarantor on account of such subrogation rights at any time
when all of the Guaranteed Obligations and all amounts owing hereunder shall not
have been paid in full, such amount shall be held by the Guarantor in trust for
Collateral Agent and the Beneficiaries, segregated from other funds of the
Guarantor, and shall, forthwith upon receipt by the Guarantor, be turned over to
Collateral Agent in the exact form received by the Guarantor (duly indorsed by
the Guarantor to Collateral Agent, if required), to be applied against the
Guaranteed Obligations, whether matured or unmatured, in such order as set forth
in Section 13 of the Participation Agreement.

           5. Amendments, etc. with respect to the Guaranteed Obligations;
              -----------------------------------------------------------
Waiver of Rights. The Guarantor shall remain obligated hereunder notwithstanding
----------------
that, without any reservation of rights against the Guarantor and without notice
to or further assent by the Guarantor, any demand for payment of any of the
Guaranteed Obligations made by Collateral Agent or any Beneficiary may be
rescinded by such party and any of the Guaranteed Obligations continued, and the
Guaranteed Obligations, or the liability of any other party upon or for any part
thereof, or any collateral security or guarantee therefor or right of offset
with respect thereto, may, from time to time in accordance with the respective
terms thereof, in whole or in part, be renewed, extended, amended, modified,
accelerated, compromised, waived, surrendered or released by Collateral Agent or
any Beneficiary, and the SPC Loan Agreement, the Participation Agreement and the
other Operative Agreements may be amended, modified, supplemented or terminated,
in whole or in part, from time to time, and any collateral security, guarantee
or right

                                       4
<PAGE>

of offset at any time held by Collateral Agent or any Beneficiary for the
payment of the Guaranteed Obligations may be sold, exchanged, waived,
surrendered or released. Neither Collateral Agent nor any Beneficiary shall have
any obligation to protect, secure, perfect or insure any Lien at any time held
by it as security for the Guaranteed Obligations or for this Guarantee or any
property subject thereto. When making any demand hereunder against the
Guarantor, Collateral Agent or any Beneficiary may, but shall be under no
obligation to, make a similar demand on the Lessor or any other guarantor, and
any failure by Collateral Agent or any Beneficiary to make any such demand or to
collect any payments from the Lessor or any other guarantor or any release of
the Lessor or such other guarantor shall not relieve the Guarantor from its
obligations under this Guarantee, and shall not impair or affect the rights and
remedies, express or implied, or as a matter of law, of Collateral Agent or any
Beneficiary against the Guarantor. For the purposes hereof "demand" shall
include the commencement and continuance of any legal proceedings.

           6. Guarantee Absolute and Unconditional. The Guarantor waives any and
              ------------------------------------
all notice of the creation, renewal, extension or accrual of any of the
Guaranteed Obligations and notice of or proof of reliance by Collateral Agent or
any Beneficiary upon this Guarantee or acceptance of this Guarantee; the
Guaranteed Obligations, and any of them, shall conclusively be deemed to have
been created, contracted or incurred, or renewed, extended, amended or waived,
in reliance upon this Guarantee; and all dealings between the Lessor and the
Guarantor, on the one hand, and Collateral Agent and the Beneficiaries, on the
other hand, likewise shall be conclusively presumed to have been had or
consummated in reliance upon this Guarantee. The Guarantor waives diligence,
presentment, protest, demand for payment and notice of default or nonpayment to
or upon the Lessor or the Guarantor with respect to the Guaranteed Obligations.
The Guarantor understands and agrees that this Guarantee shall be construed as a
continuing, absolute and unconditional guarantee and surety of payment without
regard to (a) the validity, regularity or enforceability of the SPC Loan
Agreement or any other Operative Agreement, any of the Guaranteed Obligations or
any other collateral security therefor or guarantee or right of offset with
respect thereto at any time or from time to time held by Collateral Agent or any
Beneficiary, (b) any defense, set-off or counterclaim (other than a defense of
payment or performance) which may at any time be available to or be asserted by
the Lessor or the Guarantor against Collateral Agent or any Beneficiary, or (c)
any other circumstance whatsoever (with or without notice to or knowledge of the
Lessor or the Guarantor) which constitutes, or might be construed to constitute,
an equitable or legal discharge of the Lessor for the Guaranteed Obligations, or
of the Guarantor under this Guarantee, in bankruptcy or in any other instance.
When pursuing its rights and remedies hereunder against the Guarantor,
Collateral Agent and any Beneficiary may, but shall be under no obligation to,
pursue such rights and remedies as it may have against the Lessor or any other
Person or against any collateral security or guarantee for the Guaranteed
Obligations or any right of offset with respect thereto, and any failure by
Collateral Agent or any Beneficiary to pursue such other rights or remedies or
to collect any payments from the Lessor or any such other Person or to realize
upon any such collateral security or guarantee or to exercise any such right of
offset, or any release of the Lessor or any such other Person or any such
collateral security, guarantee or right of offset, shall not relieve the
Guarantor of any liability hereunder, and shall not impair or affect the rights
and remedies, whether express, implied or available as a matter of law, of
Collateral Agent and the Beneficiaries against the Guarantor. This Guarantee
shall remain in full force and effect and be binding in accordance with and to
the extent of its terms upon the Guarantor and the successors and assigns
thereof, and

                                       5
<PAGE>

shall inure to the benefit of Collateral Agent and the Beneficiaries, and their
respective successors, indorsees, transferees and assigns, until all the
Guaranteed Obligations and the obligations of the Guarantor under this Guarantee
shall have been satisfied by payment in full, notwithstanding that from time to
time during the term of the SPC Loan Agreement, Lease and other Operative
Agreements the Lessor may be free from any Guaranteed Obligations.

           7. Reinstatement. This Guarantee shall continue to be effective, or
              -------------
be reinstated, as the case may be, if at any time payment, or any part thereof,
of any of the Guaranteed Obligations is rescinded or must otherwise be restored
or returned by Collateral Agent or any Beneficiary upon the insolvency,
bankruptcy, dissolution, liquidation or reorganization of the Lessor or the
Guarantor, or upon or as a result of the appointment of a receiver, intervenor
or conservator of, or trustee or similar officer for, the Lessor or the
Guarantor or any substantial part of its property, or otherwise, all as though
such payments had not been made.

           8. Payments. The Guarantor hereby guarantees that payments hereunder
              --------
will be paid to Collateral Agent without set-off or counterclaim in Dollars at
the office of Collateral Agent located at 450 West 33rd Street, New York, New
York 10001. If demand is made for payment under this Guarantee at or prior to
11:00 a.m. Eastern Standard Time on a Business Day, payment shall be due
hereunder on or before the close of such Business Day; otherwise, payment shall
be due before the close of the next succeeding Business Day after such demand is
made.

           9. Affirmative Covenants of the Guarantor. Guarantor hereby covenants
              --------------------------------------
and agrees that so long as this Guarantee is in effect and until the SPC Loan
Commitments and the Investor Contribution Commitments have terminated and the
Guaranteed Obligations and all amounts owing hereunder are paid in full the
Guarantor will:

          9.1   Financial Statements.  Furnish to the Collateral Agent:
          --------------------------

          (a) as soon as available for distribution to shareholders and
          creditors generally, but in any event within 120 days after the end of
          each fiscal year of Immunex, a copy of the consolidated balance sheet
          of Immunex and its consolidated Subsidiaries, as of the end of such
          fiscal year and the related consolidated statements of income and
          retained earnings and of cash flows for such fiscal year, setting
          forth in each case in comparative form the figures for the previous
          fiscal year, reported on without a "going concern" or like
          qualification or exception, or qualification arising out of the scope
          of the audit, by Ernst & Young or other independent certified public
          accountants of nationally recognized standing and reasonably
          acceptable to the Collateral Agent;

          (b) as soon as available for distribution to shareholders and
          creditors generally, but in any event within 90 days after the end of
          each fiscal year of Immunex, a copy of the unaudited consolidated
          balance sheet of Immunex and its consolidated Subsidiaries, as at the
          end of such year, and the related unaudited consolidated statements of
          income and retained earnings and of cash flows for such year, in each
          case setting forth in comparative form the figures for the
          corresponding

                                       6
<PAGE>

          period of the previous year and the figures for such period as shown
          on the budgets of Immunex for such year; and

          (c) as soon as available, but in any event not later than 45 days
          after the end of each of the first three quarterly periods of each
          fiscal year of Immunex, the unaudited consolidated balance sheet of
          Immunex and its consolidated Subsidiaries, as at the end of such
          quarter, and the related unaudited consolidated statements of income
          and retained earnings and of cash flows of Immunex and its
          consolidated Subsidiaries, for such quarter and the portion of the
          fiscal year through the end of such quarter, setting forth in each
          case in comparative form the figures for the corresponding period of
          the previous fiscal year, certified by a Responsible Officer of
          Immunex as being fairly stated in all material respects when
          considered in relation to the consolidated financial statements of
          Immunex and its consolidated Subsidiaries, (subject to normal year-end
          audit adjustments), and in each case setting forth in comparative form
          the figures for such periods as shown on the budgets of such Person
          for such year; and

          (d) as soon as available, copies of its Current SEC Reports, if any;

all such financial statements to be complete and correct in all material
respects and to be prepared in reasonable detail and in accordance with GAAP
applied consistently throughout the periods reflected therein and with prior
periods (except as approved by such accountants or officer, as the case may be,
and disclosed therein).

          9.2   Certificates; Other Information. Furnish to the Collateral
          -------------------------------------
Agent:

          (a) concurrently with the delivery of the financial statements
          referred to in Section 9.1(a), or as a component thereof, a
          certificate of the independent certified public accountants reporting
          on such financial statements stating that in making the examination
          necessary therefor no knowledge was obtained of any Default or Event
          of Default, except as specified in such certificate;

          (b) concurrently with the delivery of the financial statements
          referred to in Sections 9.1(a) and 9.1(c), a certificate of a
          Responsible Officer of Immunex stating that, to the best of such
          Responsible Officer's knowledge, Guarantor during such period has
          observed or performed all of its covenants and other agreements, and
          satisfied every material condition, contained in this Guarantee and
          the other Operative Agreements to which it is a party to be observed,
          performed or satisfied by it, and that such Responsible Officer has
          obtained no knowledge of any Default or Event of Default except as
          specified in such certificate;

          (c) (i) within five days after the same are sent, copies of all
          financial statements and reports which Immunex, if at such time any
          class of Immunex's securities are held by the public, sends to its
          stockholders generally, or, if otherwise, such financial statements
          and reports as are made generally available to the public, and (ii)
          within five days after the same are filed, copies of all financial
          statements and

                                       7
<PAGE>

          reports which Immunex may make to, or file with, the Securities and
          Exchange Commission or any successor or analogous Governmental
          Authority;

          (d) promptly, such additional financial and other information as the
          Beneficiaries or the Collateral Agent may from time to time reasonably
          request.

          9.3 Payment of Obligations. Pay, discharge or otherwise satisfy at or
          --------------------------
before maturity or before they become delinquent, as the case may be, all its
material obligations of whatever nature, except where the amount or validity
thereof is currently being contested in good faith by appropriate proceedings
and reserves in conformity with GAAP with respect thereto have been provided on
the books of Guarantor or any Subsidiary of Guarantor, as the case may be.

          9.4 Conduct of Business and Maintenance of Existence. Continue to
          ----------------------------------------------------
engage in business in the same general type of industry or industries in which
its business is now conducted by it, and, in conjunction therewith, in any
industry or industries complementary thereto as reasonably determined by
Immunex, and preserve, renew and keep in full force and effect its corporate
existence and take all reasonable action to maintain all rights, privileges and
franchises necessary or desirable in the normal conduct of its business except
as otherwise permitted pursuant to Section 9.5, provided, that Immunex may
re-incorporate under the laws of the State of Delaware in accordance with
applicable Legal Requirements and upon thirty (30) days prior written notice to
Collateral Agent; comply with all Contractual Obligations and Legal Requirements
except to the extent that failure to comply therewith would not, in the
aggregate, reasonably be expected to have a Material Adverse Effect.

          9.5 Maintenance of Property; Insurance. Guarantor will, and will
          --------------------------------------
cause each of its consolidated Subsidiaries to, (a) keep and maintain all
property material to the conduct of its business in good working order and
condition, casualty, condemnation and ordinary wear and tear excepted, and
promptly repair or replace such property following any damage thereto, and (b)
maintain, with financially sound and reputable insurance companies, insurance in
such amounts and against such risks as are customarily maintained by companies
engaged in the same or similar businesses operating in the same or similar
locations.

          9.6 Inspection of Property; Books and Records; Discussions. Keep
          ----------------------------------------------------------
proper books of records and account in which full, true and correct entries in
conformity with GAAP and all Legal Requirements shall be made of all dealings
and transactions in relation to its business and activities; and permit
representatives of Collateral Agent to visit and inspect any of its properties
and examine and make abstracts from any of its books and records at any
reasonable time and as often as may reasonably be desired in accordance with
Section 10.3 of the Lease, and to discuss the business, operations, properties
and financial and other condition of Guarantor and Subsidiaries of Guarantor
with officers and employees of Guarantor and Subsidiaries of Guarantor and with
its independent certified public accountants; provided, however, that no such
visit, inspection or examination or discussion shall unreasonably disrupt or
interfere with normal operations of Guarantor or any of its Subsidiaries and any
such representatives of the Beneficiaries and the Collateral Agent shall be
accompanied by a Responsible Officer of Guarantor. No failure to comply with any
request for the exercise of rights hereunder shall be

                                       8
<PAGE>

cause for any Event of Default unless such request is submitted in writing to
Guarantor with reference to this Section 9.6.

           9.7   Notices. Promptly give notice to the Beneficiaries and the
           -------------
Collateral Agent of:

           (a) the occurrence of any Default or Event of Default of which
           Guarantor has actual knowledge;

           (b) any (i) default or event of default by Guarantor or any of its
           Subsidiaries under or with respect to any of their respective
           Contractual Obligations in any respect which, if not cured, would
           reasonably be expected to have a Material Adverse Effect, or to
           Guarantor's knowledge any default or event of default by any third
           party under or with respect to any Contractual Obligation of said
           third party with Guarantor or any of its Subsidiaries in a respect
           which, if not cured, would reasonably be expected to have a Material
           Adverse Effect or (ii) litigation, investigation or proceeding of
           which Guarantor has actual knowledge which may exist at any time
           between Guarantor or any Subsidiary of Guarantor and any Governmental
           Authority, which in either case, if not cured or if adversely
           determined, as the case may be, would reasonably be expected to have
           a Material Adverse Effect;

           (c) any litigation or proceeding affecting Guarantor or any
           Subsidiary of Guarantor of which Guarantor has actual knowledge in
           which the amount involved is reasonably anticipated by Guarantor to
           exceed $15,000,000 or more and not covered by insurance or in which
           injunctive or similar relief is sought and which if adversely
           determined would reasonably be expected to have a Material Adverse
           Effect;

           (d) the following events, as soon as possible and in any event within
           30 days after Guarantor has actual knowledge thereof: (i) the
           occurrence or expected occurrence of any Reportable Event with
           respect to any Plan, or any withdrawal from, or the termination,
           Reorganization or Insolvency of any Multiemployer Plan or (ii) the
           institution of proceedings or the taking of any other action by the
           PBGC or Guarantor, any Commonly Controlled Entity with respect to the
           termination of any Single Employer Plan; and

           (e) (i) a development or event which has had or would reasonably be
           expected to result in the Fixed Charge Ratio being less than 1.0 to
           1, or (ii) any action by the Food and Drug Administration ("FDA")
                                                                       ---
           which causes Immunex to operate under a consent decree, or (iii) any
           action by the FDA which causes Immunex to cease production of Enbrel.

Each notice pursuant to this subsection shall be accompanied by a statement of a
Responsible Officer setting forth details of the occurrence referred to therein
and stating what action Guarantor proposes to take with respect thereto.

                                       9
<PAGE>

           9.8 Environmental Laws. (a) Comply in all material respects with, and
           ----------------------
undertake all reasonable efforts to ensure compliance by all tenants and
subtenants, if any, with, all Environmental Laws and obtain and comply in all
material respects with and maintain, and undertake all reasonable efforts to
ensure that all tenants and subtenants obtain and comply with and maintain, any
and all licenses, approvals, registrations or permits required by Environmental
Laws, and upon discovery of any non-compliance or suspected non-compliance,
undertake all reasonable efforts to attain material compliance;

           (b) Conduct and complete all investigations, studies, sampling and
testing, and all remedial, removal and other actions required under
Environmental Laws and promptly comply in all material respects with all lawful
orders and directives of all Governmental Authorities respecting Environmental
Laws, except to the extent that the failure to so conduct, complete or take such
actions, or to comply with such orders and directives, would not in the
aggregate reasonably be expected to have a Material Adverse Effect;

           (c) Defend, indemnify and hold harmless the Lessor, the Beneficiaries
and the Collateral, and their respective employees, agents, officers and
directors, from and against any claims, demands, penalties, fines, liabilities,
settlements, damages, costs and expenses of whatever kind or nature known or
unknown, contingent or otherwise, arising out of, or in any way relating to the
violation of or noncompliance with any Environmental Laws applicable to the real
property owned or operated by Guarantor or any Subsidiary of Guarantor, or any
orders, requirements or demands of Governmental Authorities related thereto,
including, without limitation, reasonable attorney's and consultant's fees,
investigation and laboratory fees, court costs and litigation expenses, except
to the extent that any of the foregoing arise out of the gross negligence or
willful misconduct of the party seeking indemnification therefore; and

           (d) Maintain a program to identify and promote substantial compliance
with and to minimize prudently any liabilities or potential liabilities under
any Environmental Law that may affect Guarantor or any of its Subsidiaries.

           9.9 Subsequent Guarantees. Immunex shall cause each Subsidiary of
           -------------------------
Immunex for which the aggregate value of all assets owned by such Subsidiary is
or becomes greater than the lesser of (x) five percent (5%) of Total Assets as
of the last day of the immediately preceding fiscal quarter of Immunex, (y) five
percent (5%) of Total Revenues for the twelve (12) month period ended on the
immediately preceding fiscal quarter, and (z) five percent (5%) of EBITDA
(without giving effect to this sentence) for the twelve (12) month period ended
on the immediately preceding fiscal quarter, to execute an amendment to this
Guarantee, whereby such Subsidiary becomes a party hereto promptly after the
later of (i) the date on which such Subsidiary becomes a Subsidiary of Immunex
and (ii) the date on which such Subsidiary's assets attain an aggregate value in
excess of the lesser of (x) five percent (5%) of Total Assets as of the last day
of the immediately preceding fiscal quarter of Immunex, (y) five percent (5%) of
Total Revenues for the twelve (12) month period ended on the immediately
preceding fiscal quarter, and (z) five percent (5%) of EBITDA (without giving
effect to this sentence) for the twelve (12) month period ended on the
immediately preceding fiscal quarter; provided, that each Person required to
                                      --------  ----
become a party hereto by this Section 9.9 which becomes a Subsidiary of Immunex
after the date hereof shall only be required to become a party to the extent not
prohibited by such Person's existing contractual obligations in the event that
such contractual obligations existed at

                                       10
<PAGE>

the time such Person became a Subsidiary and were not created in anticipation
thereof. If at any time after such Person becomes a Subsidiary of Immunex any
such contractual prohibition ceases to exist, then such Subsidiary shall be
required to become a party to this Guarantee as provided above in this Section
9.9.

           10.  Negative Covenants. Immunex hereby agrees that so long as this
                ------------------
Guarantee is in effect and until the SPC Loan Commitments and the Investor
Contribution Commitments have terminated and the Guaranteed Obligations and all
amounts owing hereunder are paid in full, Immunex shall not, directly or
indirectly:

          10.1  Financial Condition Covenants.
          -----------------------------------

          (a)   Leverage Ratio. Permit the Leverage Ratio at any time to be
                --------------
greater than 2.0 to 1.0.

          (b)   Fixed Charge Ratio. Permit the Fixed Charge Ratio for the four
                ------------------
          (4) consecutive fiscal quarters of Immunex ending with any fiscal
          quarter set forth below to be less than the ratio set forth opposite
          such fiscal quarter:

<TABLE>
<CAPTION>
                               Four Fiscal Quarters              Fixed Charge Ratio
                               --------------------              ------------------
                                        Ended
                                        -----
                           -------------------------------- ----------------------------
                           <S>                              <C>
                           December 31, 2001                1.75 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2002                1.75 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2003                2.0 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2004                2.0 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2005                3.0 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2006                3.0 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2007                3.0 to 1.0
                           -------------------------------- ----------------------------
                           December 31, 2008                3.0 to 1.0
                           -------------------------------- ----------------------------
</TABLE>

          10.2 Limitation on Liens. Create, incur, assume or suffer to exist any
          ------------------------
Lien upon any of its property, assets or revenues (other than the Property),
whether now owned or hereafter acquired, except for Permitted Encumbrances and
the following:

          (a) Liens for taxes not yet due or which are being contested in good
          faith by appropriate proceedings, provided that adequate reserves with
          respect thereto are maintained on the books of Immunex or any
          Subsidiary of Immunex, as the case may be, in conformity with GAAP;

                                       11
<PAGE>

          (b) carriers', warehousemen's, mechanics', materialmen's, repairmen's
          or other like Liens arising in the ordinary course of business which
          are not overdue for a period of more than 60 days or which are being
          contested in good faith by appropriate proceedings;

          (c) Liens of any of the types referred to in clause (b) above that
          have been bonded for not less than the full amount in dispute (or as
          to which other security arrangements satisfactory to the Agent have
          been made), which bonding (or arrangements) shall comply with
          applicable Legal Requirements, and shall have effectively stayed any
          execution or enforcement of such Liens;

          (d) Liens arising out of judgments or awards with respect to which
          appeals or other proceedings for review are being prosecuted in good
          faith and for the payment of which adequate reserves have been
          provided as required by GAAP or other appropriate provisions have been
          made, so long as such proceedings have the effect of staying the
          execution of such judgments or awards;

          (e) Liens in favor of municipalities to the extent agreed to by the
          Lessor or permitted under the Participation Agreement or other
          Operative Agreements;

          (f) rights of any sublessee or assignee under a sublease or an
          assignment expressly permitted by the terms of the Lease for no longer
          than the duration of the Lease;

          (g) pledges or deposits in connection with workers' compensation,
          unemployment insurance and other social security legislation and
          deposits securing liability to insurance carriers under insurance or
          self insurance arrangements;

          (h) deposits to secure the performance of bids, trade contracts (other
          than for borrowed money), leases, statutory obligations, surety and
          appeal bonds, performance bonds and other obligations of a like nature
          incurred in the ordinary course of business;

          (i) easements, rights-of-way, restrictions and other similar
          encumbrances incurred in the ordinary course of business which, in the
          aggregate, are not substantial in amount and which do not in any case
          materially detract from the value of the property subject thereto or
          materially interfere with the ordinary conduct of the business of
          Immunex or any of its Subsidiaries;

          (j) Liens in favor of customs and revenue authorities arising as a
          matter of law to secure payment of custom duties in connection with
          the importation of goods so long as such Liens attach only to the
          imported goods;

          (k) Liens now or hereafter granted in favor of the Administrative
          Agent, SPC, the Collateral Agent or other Person pursuant to the
          Operative Agreements; and

                                       12
<PAGE>

          (l) Liens not otherwise permitted in clauses (a)-(k) above securing
          Indebtedness not exceeding, when taken together with the aggregate
          value of the assets which are subject to arrangements with any Person
          where Immunex or any of the Subsidiaries of Immunex is the lessee of
          real or personal property which has been or is to be sold or
          transferred by Immunex or such Subsidiary to such Person or to any
          other Person to whom funds have been or are to be advanced by such
          Person on the security of such property or rental obligations of
          Immunex or such Subsidiary, thirty-five percent (35%) of Total Assets.

          10.3 Limitations on Fundamental Changes. Enter into any merger,
          ---------------------------------------
consolidation or amalgamation, or liquidate, wind up or dissolve itself (or
suffer any liquidation or dissolution), or convey, sell, lease, assign, transfer
or otherwise dispose of, all or substantially all of its property, business or
assets, except:

          (a) any Subsidiary of Immunex may take any of the foregoing actions;
          provided, that, after giving pro form effect to such action, Guarantor
          --------
          shall be in compliance with all covenants hereunder;

          (b) Guarantor may be merged or consolidated with or into any other
          Person, provided, that Guarantor shall be the continuing or surviving
                  --------
          corporation and after giving pro form effect to such merger or
          consolidation, Guarantor shall be in compliance with all covenants
          hereunder; and

          (c) pursuant to the Operative Agreements.

          10.4 Limitation on Sale or Lease of Assets. Convey, sell, lease,
          ------------------------------------------
assign, transfer or otherwise dispose of any of its property, business or assets
(including, without limitation, receivables and leasehold interests), whether
now owned or hereafter acquired, except:

          (a) obsolete or worn out property disposed of in the ordinary course
          of business;

          (b) the sale of inventory in the ordinary course of business;

          (c) the sale by Immunex or its Subsidiaries of those lines of business
          identified on Schedule 10.4(c);
                        ----------------

          (d) the sale or discount without recourse of defaulted accounts
          receivable arising in the ordinary course of business in connection
          with the compromise or collection thereof;

          (e) as permitted by Section 10.3;

          (f) the lease by a Subsidiary as lessor of real estate properties to
          Immunex or any Subsidiary of Immunex for use by Immunex or such
          Subsidiary as the site of its offices and facilities;

          (g) pursuant to the Operative Agreements; and

                                       13
<PAGE>

          (h) the conveyance, sale, lease, assignment, transfer or other
          disposal of property, business or assets of Immunex and its
          Subsidiaries which are not material to a principal business of
          Immunex, provided such sale could not reasonably be expected to have a
          Material Adverse Effect.

          10.5 Limitation on Dividends. Declare or pay any dividend (other than
          ----------------------------
dividends payable solely in common stock of such Person) on, or make any payment
on account of, or set apart assets for a sinking or other analogous fund for,
the purchase, redemption, defeasance, retirement or other acquisition of, any
shares of any class of Capital Stock of such Person or any warrants or options
to purchase any such Capital Stock, whether now or hereafter outstanding, or
make any other distribution in respect thereof, either directly or indirectly,
whether in cash or property or in obligations of Immunex or any Subsidiary of
Immunex, except that if no Default or Event of Default exists or would
reasonably be expected to be caused thereby (i) Subsidiaries of Guarantor may
declare and pay dividends to Guarantor and other shareholders of such
Subsidiaries, and (ii) during any fiscal year of Immunex following the Closing
Date, Immunex shall be permitted to declare cash dividends or repurchase its
Capital, provided that after giving pro forma effect to the any such
declarations, payments or repurchases, Guarantor shall be in compliance with all
other covenants hereunder.

          10.6 Nature of Business. Engage in any principal business other than
          -----------------------
business in the same general type of industry or industries in which its
business is now conducted, or in conjunction therewith, in any industry or
industries complementary thereto as reasonably determined by Immunex.

          10.7 Change in Control. Permit or otherwise allow either (i) a
          ----------------------
"person" or a "group" (within the meaning of Sections 13(d) and 14(d)(2) of the
Securities Exchange Act) other than American Home Products Corporation, a
Delaware corporation (or its affiliates or successors) to become the "beneficial
owner" (as defined in Rule 13d-3 under the Securities Exchange Act) of more than
50% of the then outstanding voting stock of Immunex, or (ii) a majority of the
Board of Directors of Immunex to consist of individuals who are not Continuing
Directors; "Continuing Director" means, as of any date of determination, (x) an
            -------------------
individual who on the date two (2) years prior to such determination date was a
member of Immunex's Board of Directors, or (y) any new director whose election
or nomination for election by Immunex's shareholders, was approved by a vote of
at least a majority of the directors then still in office who either were
directors on the date two (2) years prior to such determination date or whose
election, or nomination for election, was previously so approved.

          11. Notices. All notices, requests and demands to or upon Collateral
              -------
Agent, any Beneficiary or the Guarantor to be effective shall be in writing
(including by telecopy) by United States certified or registered mail (postage
prepaid), by nationally recognized courier service, by hand or by telecopy with
confirming notice and any such notice shall become effective upon receipt and
shall be directed to any Beneficiary or Guarantor, as the case may be, at each
of their respective addresses or transmission numbers for notices provided in
Section 14.3 of the Participation Agreement. Each Beneficiary and the Guarantor
may change its address and transmission numbers for notices by notice in the
manner provided in Section 14.3 of the Participation Agreement.

                                       14
<PAGE>

           12. Severability. Any provision of this Guarantee that is prohibited
               ------------
or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

           13. Integration. This Guarantee and other applicable Operative
               -----------
Agreements represent the agreement of the Guarantor with respect to the subject
matter hereof and there are no promises or representations by Collateral Agent
or any Beneficiary relative to the subject matter hereof not reflected herein.

           14. Amendments in Writing; No Waiver; Cumulative Remedies. (a) None
               -----------------------------------------------------
of the terms or provisions of this Guarantee may be waived, amended,
supplemented or otherwise modified except as provided in Section 14.5 of the
Participation Agreement.

           (b) Neither Collateral Agent nor any Beneficiary shall, by any act
(except by a written instrument pursuant to Section 14(a) hereof), delay,
indulgence, omission or otherwise be deemed to have waived any right or remedy
hereunder or to have acquiesced in any Default or Event of Default or in any
breach of any of the terms and conditions hereof. No failure to exercise, nor
any delay in exercising, on the part of Collateral Agent or any Beneficiary, any
right, power or privilege hereunder shall operate as a waiver thereof. No single
or partial exercise of any right, power or privilege hereunder shall preclude
any other or further exercise thereof or the exercise of any other right, power
or privilege. A waiver by Collateral Agent or any Beneficiary of any right or
remedy hereunder on any one occasion shall not be construed as a bar to any
right or remedy that Collateral Agent or such Beneficiary would otherwise have
on any future occasion.

           (c) The rights and remedies herein provided are cumulative, may be
exercised singly or concurrently and are not exclusive of any other rights or
remedies provided by law.

           15. Section Headings. The section headings used in this Guarantee are
               ----------------
for convenience of reference only and are not to affect the construction hereof
or be taken into consideration in the interpretation hereof.

           16. Successors and Assigns. This Guarantee shall be binding upon the
               ----------------------
successors and assigns of the Guarantor and shall inure to the benefit of
Collateral Agent and the Beneficiaries and their successors and permitted
assigns.

           17. SUBMISSION TO JURISDICTION; WAIVERS. (a) THE GUARANTOR HEREBY
               -----------------------------------
IRREVOCABLY AND UNCONDITIONALLY:

               (i) SUBMITS FOR ITSELF AND ITS PROPERTY IN ALL LEGAL ACTIONS OR
           PROCEEDINGS RELATING TO THIS GUARANTEE OR ANY OTHER OPERATIVE
           AGREEMENT TO WHICH IT IS A PARTY, OR FOR RECOGNITION AND ENFORCEMENT
           OF ANY JUDGMENT IN RESPECT THEREOF TO THE NON-EXCLUSIVE GENERAL
           JURISDICTION OF THE COURTS OF THE STATE OF NEW YORK AND THE COURTS OF
           THE

                                       15
<PAGE>

           UNITED STATES LOCATED IN THE SOUTHERN DISTRICT OF NEW YORK, AND
           APPELLATE COURTS THEREOF;

               (ii)  CONSENTS THAT ANY SUCH ACTION OR PROCEEDING MAY BE BROUGHT
           IN SUCH COURT, WAIVES ANY OBJECTION THAT IT MAY HAVE NOW OR HEREAFTER
           TO THE VENUE OF ANY SUCH ACTION OR PROCEEDING IN ANY SUCH COURT AND
           WAIVES ANY OBJECTION THAT SUCH ACTION OR PROCEEDING IN ANY SUCH COURT
           WAS BROUGHT IN AN INCONVENIENT FORUM AND AGREES NOT TO PLEAD, CLAIM
           OR ASSERT THE SAME;

               (iii) AGREES THAT SERVICE OF PROCESS IN ANY SUCH ACTION OR
           PROCEEDING IN ANY SUCH COURT MAY BE EFFECTED BY MAILING A COPY
           THEREOF BY REGISTERED OR CERTIFIED MAIL (OR ANY SUBSTANTIALLY SIMILAR
           FORM OF MAIL), POSTAGE PREPAID TO, OR BY PERSONAL SERVICE AT, ITS
           ADDRESS SET FORTH HEREIN OR SUCH OTHER ADDRESS OF WHICH THE AGENT
           SHALL HAVE BEEN NOTIFIED PURSUANT HERETO, WHETHER OR NOT SUCH ADDRESS
           BE WITHIN THE JURISDICTION OF ANY SUCH COURT;

               (iv)  AGREES THAT NOTHING HEREIN SHALL AFFECT THE RIGHT TO EFFECT
           SERVICE OF PROCESS IN ANY OTHER MANNER PERMITTED BY LAW OR SHALL
           LIMIT THE RIGHT OF THE AGENT (AND NOT OF THIS GUARANTOR) TO SUE IN
           ANY OTHER JURISDICTION; AND

               (v)   WAIVES, TO THE MAXIMUM EXTENT NOT PROHIBITED BY LAW, ANY
           RIGHT IT MAY HAVE TO CLAIM OR RECOVER IN ANY LEGAL ACTION OR
           PROCEEDING REFERRED TO IN THIS SECTION 17 ANY SPECIAL, EXEMPLARY, OR
           PUNITIVE DAMAGES.

           (b) THE GUARANTOR HEREBY IRREVOCABLY AND UNCONDITIONALLY WAIVES TRIAL
BY JURY IN ANY LEGAL ACTION OR PROCEEDING RELATING TO THIS GUARANTEE OR ANY
OTHER OPERATIVE AGREEMENT AND FOR ANY COUNTERCLAIM THEREIN.

           18. GOVERNING LAW. THIS GUARANTEE SHALL BE GOVERNED BY, AND CONSTRUED
               -------------
AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

           19. Survival of Representations, Warranties, etc. All
               --------------------------------------------
representations, warranties, covenants and agreements made herein and in
statements or certificates delivered pursuant hereto shall survive any
investigation or inspection made by or on behalf of the Lessor and shall
continue in full force and effect until all of the obligations of the Guarantor
under this Guarantee shall be fully performed in accordance with the terms
hereof, and until the payment in full of all sums payable by the Lessee under
the Operative Agreements, and until performance in

                                       16
<PAGE>

full of all obligations of the Lessee in accordance with the terms and
provisions of such agreements.

          20.  Third Party Beneficiaries. The Guarantor expressly acknowledges
               -------------------------
and agrees that each Indemnified Person shall be a third party beneficiary of
this Guarantee.

          21.  Action by Administrative Agent. The Administrative Agent shall
               ------------------------------
only take action hereunder as directed by SPC.

                                       17
<PAGE>

          IN WITNESS WHEREOF, the undersigned has caused this Guarantee to be
duly executed and delivered by its duly authorized officer as of the day and
year first above written.

                                         IMMUNEX CORPORATION


                                         By:       /s/ David A. Mann
                                             -------------------------------
                                             Name: David A. Mann
                                             Title: Executive Vice President,
                                                      Chief Financial Officer
                                                      and Treasurer


                                         IMMUNEX MANUFACTURING CORPORATION


                                         By:       /s/ David A. Mann
                                             -------------------------------
                                             Name: David A. Mann
                                             Title: Treasurer

                                       18