Document:

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                                                                   Exhibit 10.25

                       AMENDMENT NO. 1 TO LEASE AGREEMENT

        THIS AMENDMENT NO. 1 TO LEASE AGREEMENT (this "Amendment") dated as of
March 29, 2002, but effective as of October 25, 2001, is made by and between
WELLS FARGO BANK NORTHWEST, NATIONAL ASSOCIATION, not in its individual
capacity, but solely as Owner Trustee under that certain Trust Agreement dated
as of October 25, 2001 ("Lessor") and HUMAN GENOME SCIENCES, INC., a Delaware
corporation ("Lessee"), and joined in by VAL T. ORTON, not in his individual
capacity, but solely as Maryland Trustee appointed pursuant to that certain
Trust Agreement dated as of October 25, 2001 (the "Maryland Trustee")

                                    RECITALS

        A.      Lessor and Lessee are parties to that certain Lease Agreement
dated as of October 25, 2001 (the "Facility Lease"), pursuant to which Lessor,
acting through the Maryland Trustee, subleased the premises more particularly
described in Exhibit A to the Facility Lease (the "Property") to Lessee, and
Lessee subleased the Property from Lessor, acting through the Maryland Trustee,
as evidenced by the execution and recordation of the Lease Supplement.

        B.     Lessor and Lessee have agreed to enter into this Amendment for
the sole purpose of confirming and clarifying the intent of the parties as
provided herein.

                                   AGREEMENTS

        NOW, THEREFORE, for and in consideration of the terms of this Amendment
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, Lessor and Lessee agree as follows:

        1.      Capitalized Terms.   Capitalized terms used herein but not
otherwise defined herein shall have the meanings assigned thereto in the
Facility Lease.

        2.      Amendments to Paragraph 2 of the Facility Lease.  Paragraph 2 of
the Facility Lease is hereby amended to add the following definitions thereto:

                "Claim has the meaning given to such term in the Deed of Trust."

                "Construction Recourse Amount means, with respect to the
Additional Improvements, as of any date of determination, an amount to be
determined equal to the sum of (i) 100% of the acquisition cost of the Land (if
any) and (ii) 89.9% of accrued Facility Costs, plus (iii) any amounts owed
pursuant to Section 5.1 and/or Section 5.5(b) of the Deed of Trust in any way
relating to or arising out of a Specified Event and (iv) any amounts owed
pursuant to Section 5.2 of the Deed of Trust and (v) indemnities payable
pursuant to Section 5.4 of the Deed of Trust in respect of amounts payable
pursuant to clauses (iii) and (iv), above."

                "Facility Costs has the meaning given to such term in clause (i)
of the definition of "Facility Costs" in the Indenture."

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                "Indemnitee has the meaning given to such term in the Deed of
Trust."

                "Specified Event means (i) an Event of Default described in
clause (viii) of Paragraph 17(a), (ii) fraud, misapplication of funds, illegal
acts or willful misconduct on the part of Lessee, any third party (including,
without limitation, any subcontractor) for which Lessee has control or
supervisory authority or delegated responsibility by contract or otherwise and
their respective employees, officers and agents, (iii) any act or failure to act
by Lessee, any third party (including, without limitation, any subcontractor)
for which Lessee has control or supervisory authority or delegated
responsibility by contract or otherwise and their respective employees, officers
and agents (other than failure to complete construction of the Additional
Improvements or to cause construction of the Additional Improvements to be
completed prior to the expiration of the Construction Period) or (iv) any
environmental condition existing with respect to the Property or the Land before
the Commencement Date."

                "Subsequent Holder Advances has the meaning given to such term
in the Trust Agreement.

        3.      Amendment to Paragraph 17 of the Facility Lease. Paragraph 17 of
the Facility Lease is hereby amended to add the following subparagraph (f):

                "(f) Limitation of Recourse Liability. Notwithstanding anything
set forth in this Paragraph 17 to the contrary, during the Construction Period,
upon the occurrence of an Event of Default, unless such Event of Default is, is
caused by or results from a Specified Event (in which event the limitations
contained in this subparagraph(f) shall not apply), the aggregate amount payable
by Lessee on a recourse basis under this Paragraph 17 in respect of the portion
of the Lease Balance advanced in connection with the construction of the
Additional Improvements (the "Construction Lease Balance") shall be limited to
the Construction Recourse Amount. Concurrently with the payment of the
Construction Recourse Amount, Lessee shall, immediately upon request by Lessor,
relinquish possession of the Property in the condition required by this Lease,
subject only to the Head Lease and the Deed of Trust and, immediately upon
request by Lessor, convey by deed or other instrument all of Lessee's right,
title and interest in and to the Property to Lessor or a party designated by
Lessor, subject only to the Head Lease and the Deed of Trust. The foregoing
limitation on recourse liability will not apply (i) with respect to any Event of
Default caused by or resulting from a Specified Event, (ii) any portion of the
Lease Balance other than the Construction Lease Balance (the "Completed Property
Lease Balance") or (iii) from and after the Substantial Completion Date.
Notwithstanding the foregoing limitation on recourse liability, (x) Lessee shall
have full recourse liability for the Completed Property Lease Balance, (y)
Lessor shall have the right to proceed against the Property (including, without
limitation, the Additional Improvements) and the Land and to exercise any and
all rights and remedies hereunder and under the other Operative Documents with
respect to the Property and to recover the remaining outstanding Lease Balance
and all other amounts due and owing hereunder and under the other Operative
Documents from the proceeds of any sale, lease or other disposition thereof, and
(z) each Indemnitee shall have the right to seek indemnification from Lessee for
any Claim pursuant to Article V of the Deed of Trust."

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        4.      Amendment to Exhibit C to the Facility Lease.     Exhibit C to
the Facility Lease is hereby amended and restated as follows:

                                   "BASIC RENT

        Subject to adjustment as provided in Paragraph 6(b) of this Lease, Basic
Rent, on each Payment Date, shall be an amount equal to the sum of (i) the
amount of interest payable on the aggregate sum of the outstanding principal
amount of the Bonds as of such Payment Date, (ii) the yield payable on the
aggregate sum of the outstanding principal amount of the Certificate as of such
Payment Date, and (iii) any other amounts and costs payable or reimbursable
pursuant to the Operative Documents as of such Payment Date, including, without
limitation, any amounts to be paid or reimbursable by the Issuer, and the Lessor
under the MEDCO Note, the Letter of Credit Documents and the Head Lease;
provided, however, during the Construction Period, (a) the interest payable on
that portion of the aggregate sum of the outstanding principal amount of the
Bonds used to establish the Facility Fund shall be treated as Facility Costs and
paid by the Lessee from the Facility Fund and (b) the yield payable on that
portion of the aggregate sum of the outstanding principal amount of the
Certificate used to fund Subsequent Holder Advances shall be capitalized and
added to the outstanding principal amount of the Certificate in accordance with
Section 3.2(c) of the Trust Agreement."

        5.      No Default or Event of Default.     Lessee represents and
warrants to Lessor that, as of the date hereof, no Default or Event of Default
has occurred and is continuing, or will occur as a result of, or after giving
effect to, this Amendment.

        6.      Ratification of Facility Lease.        Except as expressly
amended by this Amendment, the Facility Lease is hereby ratified and reaffirmed
and shall continue in full force and effect.

        7.      Applicable Law.    This Amendment shall be governed by the laws
of the State of Maryland.

        8.      Counterparts. This Amendment may be executed in any number of
counterparts, each of which shall be deemed an original for all purposes, and
all counterparts shall together constitute one and the same instrument.

        9.      Joinder by Maryland Trustee. The Maryland Trustee joins herein
for the sole purpose of acknowledging and agreeing to be bound by the terms,
conditions and provisions of this Amendment.

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        IN WITNESS WHEREOF, Lessor and Lessee have caused this Amendment to be
signed on their behalf, under seal, by their respective signatories thereunto
duly organized as of the date first above written.

                                LESSOR:
                                ------

                                WELLS FARGO BANK NORTHWEST,
                                NATIONAL ASSOCIATION, not in its
                                individual capacity, but solely as
                                Owner Trustee

                                By:    /s/ Val T. Orton
                                       ------------------------------------
                                Name:  Val T. Orton
                                       ------------------------------------
                                Title: Vice President
                                       ------------------------------------

                                LESSEE:
                                ------

                                HUMAN GENOME SCIENCES, INC.

                                By:    /s/ Steven C. Mayer
                                       ------------------------------------
                                Name:  Steven C. Mayer
                                       ------------------------------------
                                Title: Senior Vice President and CFO
                                       ------------------------------------

                                MARYLAND TRUSTEE:
                                                 --------------------------

                                /s/ Val T. Orton
                                -------------------------------------------
                                Val T. Orton, not in his individual
                                capacity, but solely as Maryland
                                Trustee appointed pursuant to that
                                certain Trust Agreement dated as of
                                October 25, 2001

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                                            ACKNOWLEDGED AND APPROVED BY:

MARYLAND ECONOMIC DEVELOPMENT
CORPORATION, as Head Lessor and Issuer

By:     /s/ Hans F. Mayer
        ------------------------------
Name:   Hans F. Mayer
        ------------------------------
Title:  Executive Director
        ------------------------------

ALLFIRST TRUST COMPANY NATIONAL
ASSOCIATION, as Bond Trustee

By:     /s/ David L. Williams
        ------------------------------
Name:   David L. Williams
        ------------------------------
Title:  Senior Vice President
        ------------------------------

ALLFIRST BANK, as Credit Facility Provider,
Agent and Certificate Holder

By:     /s/ Joseph C. Lemense
        ------------------------------
Name:   Joseph C. Lemense
        ------------------------------
Title:  Senior Vice President
        ------------------------------

                                       5<PAGE>

                                                                   Exhibit 10.26
                          AMENDMENT NO. 1 TO GUARANTEE

        THIS AMENDMENT NO. 1 TO GUARANTEE (this "Amendment") dated as of March
29, 2002, but effective as of October 25, 2001, is made by and between HUMAN
GENOME SCIENCES, INC., a Delaware corporation ("Guarantor") and ALLFIRST BANK, a
Maryland banking corporation, as agent ("Agent").

                                    RECITALS

        A.      Guarantor executed a certain Guarantee in favor of Agent dated
as of October 25, 2001 (the "Guarantee"), pursuant to which Guarantor
irrevocably and unconditionally guaranteed to Agent, for the benefit of the
Beneficiaries, the full and prompt payment when due, whether by acceleration or
otherwise, and at all times thereafter, and the full and prompt performance of,
certain Liabilities.

        B.      Guarantor and Agent have agreed to enter into this Amendment for
the sole purpose of confirming and clarifying the intent of the parties
regarding the Beneficiaries of the Guarantee during the Construction Period (as
defined in the Facility Lease).

                                   AGREEMENTS

        NOW, THEREFORE, for and in consideration of the terms of this Amendment
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, Guarantor and Agent agree as follows:

        1.      Capitalized Terms.   Capitalized terms used herein but not
otherwise defined herein shall have the meanings assigned thereto in the
Guarantee.

        2.      Amendment to Section 1 of the Guarantee.   The first paragraph
of Section 1 of the Guarantee is hereby amended and restated as follows:

        "Guarantor hereby irrevocably and unconditionally guarantees to the
Agent, for the benefit of the Beneficiaries (as hereinafter defined), the full
and prompt payment when due, whether by acceleration or otherwise, and at all
times thereafter, and the full and prompt performance of, all of the Liabilities
(as hereinafter defined), including interest and yield on any such Liabilities,
whether accruing before or after any bankruptcy or insolvency case or proceeding
involving Guarantor or any other Person (as defined in the Facility Lease), and,
if interest or yield on any portion of such obligations ceases to accrue by
operation of law by reason of the commencement of such case or proceeding,
including such interest and yield as would have accrued on any such portion of
such obligations if such case or proceeding had not commenced, and further
agrees to pay all expenses (including attorneys' fees and legal expenses) paid
or incurred by any Beneficiary in endeavoring to collect the Liabilities, or any
part thereof, and in enforcing this Guarantee. The term "Liabilities", as used
herein, shall mean all of the following (without duplication), in each case
howsoever created, arising or evidenced, whether direct or indirect, joint or
several, absolute or contingent, or now or hereafter existing, or due or

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to become due: (i) all amounts now or hereafter payable by the Issuer under the
Letter of Credit Agreement, (ii) all amounts now or hereafter payable by the
Trust under the Trust Agreement, (iii) all amounts now or hereafter payable by
the Issuer under the Hedge Agreement and (iv) all amounts now or hereafter
payable under the Facility Lease and any of the other Operative Documents (in
each case whether or not Guarantor or any other Person shall be relieved or
released from any or all liability or obligations under any of the Operative
Documents, except on account of the full and indefeasible payment of all the
Liabilities and full and strict compliance by Guarantor with its obligations
hereunder); provided, however, that notwithstanding anything to the contrary
contained herein, Guarantor shall not be obligated under any circumstances to
pay under this Guaranty, and the term "Liabilities" shall not include, any
amounts greater than the Lessee (as defined in the Facility Lease) would have
had to pay, under the Facility Lease, the Deed of Trust and the other Operative
Documents, assuming that such documents were enforced in accordance with their
terms (and without giving effect to any discharge or limitation thereon
resulting or arising by reason of the bankruptcy or insolvency of the Lessee),
plus all reasonable costs actually incurred in enforcing this Guarantee. The
term "Beneficiary" and "Beneficiaries", as used herein, means (individually and
collectively) the following: (a) during the Construction Period, the Agent, for
the sole benefit of the Lessor (as defined in the Facility Lease), solely with
respect to any Liabilities attributable to the construction of the Additional
Improvements (as defined in the Facility Lease), and the Agent, for the benefit
of the Bank and the Hedge Counterparty, and their respective successors and
permitted assigns, with respect to all other Liabilities, and (b) upon
completion of construction of the Additional Improvements in accordance with the
Facility Lease, the Agent, for the benefit of the Bank and the Hedge
Counterparty, and their respective successors and permitted assigns, with
respect to all Liabilities."

        3.      Ratification of Guarantee.   Except as expressly amended by this
Amendment, the Guarantee is hereby ratified and reaffirmed and shall continue in
full force and effect.

        4.      Applicable Law.    This Amendment shall be governed by the laws
of the State of Maryland.

        5.      Counterparts. This Amendment may be executed in any number of
counterparts, each of which shall be deemed an original for all purposes, and
all counterparts shall together constitute one and the same instrument.

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        IN WITNESS WHEREOF, Guarantor and Agent have caused this Amendment to be
signed on their behalf, under seal, by their respective signatories thereunto
duly organized as of the date first above written.

                                            GUARANTOR:
                                            ---------

                                            HUMAN GENOME SCIENCES, INC.

                                            By:    /s/ Steven C. Mayer
                                                   -----------------------------
                                            Name:  Steven C. Mayer
                                                   -----------------------------
                                            Title: Senior Vice President & CFO
                                                   -----------------------------

                                            AGENT:
                                            -----

                                            ALLFIRST BANK, as Agent

                                            By:    /s/ Joseph C. Lemense
                                                   -----------------------------
                                            Name:  Joseph C. Lemense
                                                   -----------------------------
                                            Title: Senior Vice President
                                                   -----------------------------

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ACKNOWLEDGED AND APPROVED BY:

ALLFIRST BANK, as Credit Facility Provider
and Certificate Holder

By:     /s/ Joseph C. Lemense
        ------------------------------
Name:   Joseph C. Lemense
        ------------------------------
Title:  Senior Vice President
        ------------------------------

WELLS FARGO BANK NORTHWEST, NATIONAL ASSOCIATION, not in its individual
capacity, but solely as Owner Trustee, as Lessor

By:     /s/ Val T. Orton
        ------------------------------
Name:   Val T. Orton
        ------------------------------
Title:  Vice President
        ------------------------------

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