Document:

<PAGE>
                                                                  EXHIBIT 10.23

                       CASH COLLATERAL PLEDGE AGREEMENT

                                    among

                         HUMAN GENOME SCIENCES, INC.,
                                 as Pledgor,

                                ALLFIRST BANK,
                             as Agent and Pledgee

                                     and

                 ALLFIRST TRUST COMPANY NATIONAL ASSOCIATION
                             as Collateral Agent

                         Dated as of October 25, 2001

               ------------------------------------------------

<PAGE>

                       CASH COLLATERAL PLEDGE AGREEMENT

         THIS CASH COLLATERAL PLEDGE AGREEMENT (this "Agreement") is dated as
of October 25, 2001, and is among HUMAN GENOME SCIENCES, INC., a Delaware
corporation (the "Pledgor"), ALLFIRST BANK, a Maryland banking corporation, as
Agent and Pledgee (the "Agent"), and ALLFIRST TRUST COMPANY NATIONAL
ASSOCIATION, as Collateral Agent (the "Collateral Agent").

                                   RECITALS

         WHEREAS, in accordance with the provisions of Article 83A, Title 5,
Subtitle 2 of the Annotated Code of Maryland, as amended, and pursuant to a
certain Trust Indenture dated as of October 25, 2001 (the "Indenture") between
Maryland Economic Development Corporation (the "Issuer") and Allfirst Trust
Company National Association, as Trustee (the "Trustee"), the Issuer has
issued $73,000,000 in principal amount of its Taxable Variable Rate Demand
Revenue Bonds (Human Genome Sciences, Inc. Facility), Series 2001 A (the
"Bonds") to refinance a portion of the acquisition cost of certain improved
real property located in Rockville, Maryland (the "Property") and to finance
construction relating to such Property;

         WHEREAS, in order to enhance the marketability of the Bonds and
pursuant to a Letter of Credit Agreement dated as of October 25, 2001 (the
"Letter of Credit Agreement") between the Issuer and Allfirst Bank (in its
capacity as Letter of Credit issuer and Certificate Holder, the "Bank"), the
Bank has issued to the Trustee the Bank's irrevocable transferable letter of
credit to provide payment for and secure the payment of the principal of and
interest on, and the purchase price of, the Bonds;

         WHEREAS, simultaneously with the issuance of the Bonds and pursuant
to a Trust Agreement dated as of October 25, 2001 (the "Trust Agreement")
between the Bank, as Holder, and Wells Fargo Bank Northwest, National
Association, as Owner Trustee, the Bank has advanced funds for the purchase
from the HGSI Trust 2001-B (the "Trust") of $3,000,000 in principal amount of
HGSI Trust 2001-B Certificates (the "Certificates");

         WHEREAS, the Owner Trustee on behalf of the Trust has loaned the
proceeds of the advance from the Bank relating to the purchase of the
Certificates to the Issuer to refinance the remaining portion of the
acquisition cost of the Property;

         WHEREAS, pursuant to a Guarantee dated as of October 25, 2001 (the
"Guarantee"), the Pledgor has guaranteed the obligations of the Issuer to the
Bank under the Letter of Credit Agreement, the obligations of the Owner
Trustee under the Certificates (as defined in the Lease Agreement dated as of
October 25, 2001 between the Owner Trustee on behalf of the Trust, as Lessor,
and the Pledgor, as Lessee (as supplemented, the "Facility Lease")), and
certain other obligations under the Operative Documents (as defined in the
Facility Lease);

         WHEREAS, as a condition precedent to the consummation of the
transactions contemplated by the Operative Documents, the parties thereto have
required the Pledgor to post cash collateral and/or securities with a value of
not less than $76,000,000 (the "Minimum Collateral Amount");

<PAGE>

         NOW, THEREFORE, in order to secure its obligations under the
Guarantee, the Pledgor hereby covenants and agrees with the Agent as follows:

         1.       Defined Terms. All capitalized terms used but not defined
herein shall have the same meanings assigned to them in the Facility Lease.

         2.       Grant of Security Interest; Custody; Perfection. The Pledgor
hereby pledges, assigns and grants to the Agent a security interest in the
cash and marketable securities on deposit in the account maintained by the
Pledgor with the Collateral Agent as described in Exhibit A attached hereto
and made a part hereof (the "Account"), the Account, and all interest and
other income thereon and all cash and noncash proceeds thereof (all of the
foregoing is herein collectively referred to as the "Collateral") pursuant to
the provisions of the Maryland Uniform Commercial Code, in order to secure the
Pledgor's obligations under the Facility Lease and the other Operative
Documents.

         The Collateral is to be held by the Collateral Agent on behalf of the
Agent. The Pledgor hereby agrees that the Agent shall have with respect to the
Collateral the rights and remedies of a secured party provided in the Maryland
Uniform Commercial Code. The Collateral Agent will at all times maintain the
Account at its offices in the State of Maryland.

         As of the effective date of this Agreement, the Pledgor has pledged,
assigned and granted to the Agent a security interest in the Collateral and
such Collateral and the Account have been designated on the records of the
Collateral Agent as subject to the security interest granted pursuant to this
Agreement in accordance with the provisions of the Maryland Uniform Commercial
Code. The Pledgor and the Collateral Agent hereby agree that all securities or
other property underlying any financial assets credited to the Account shall
be registered in the name of the Collateral Agent, endorsed to the Collateral
Agent or in blank or credited to another securities account maintained in the
name of the Collateral Agent and in no case will any financial asset credited
to the Account be registered in the name of the Pledgor, payable to the order
of the Pledgor or specially indorsed to the Pledgor.

         The Collateral Agent hereby agrees that all property delivered to the
Collateral Agent with respect to the pledge and security intended hereby will
be held in or credited to the Account. The Collateral Agent further agrees
that each item of property (including, without limitation, any investment
property, financial asset, security, instrument, general intangible or cash)
credited to the Account shall be treated as a "financial asset" within the
meaning of Section 8-102(a)(9) of the Maryland Uniform Commercial Code.

         The Pledgor hereby directs the Collateral Agent, and the Collateral
Agent hereby agrees, to comply with all entitlement orders of the Agent with
respect to the Collateral and the Account without further consent of the
Pledgor.

         3.       Minimum Collateral Value. The Pledgor shall maintain on
deposit, in the Account, Collateral with an actual market value of not less
than the Minimum Collateral Amount, taking into account any penalties, fees,
discounts or other amounts that could result in any reduction in the actual
cash value of any of the Collateral upon any liquidation or early termination
of any investments prior to the maturity date thereof.

                                      2

<PAGE>

         4.       Investment; Preservation of Collateral. Funds held by the
Collateral Agent hereunder shall be invested and reinvested by the Collateral
Agent upon written order of the Pledgor only in Permitted Investments as
described in Exhibit B attached hereto and made a part hereof. Such
investments shall be registered in the name of the Collateral Agent and held
by the Collateral Agent for the benefit of the Agent. The Collateral Agent
shall not be responsible or liable for any loss suffered in connection with
any investment of moneys made by it in accordance with the Pledgor's
instruction.

         The Pledgor shall be responsible for the preservation of the
Collateral in the Collateral Agent's possession and shall take all action
necessary to preserve the rights of the Agent against prior parties to the
Collateral. Neither the Agent nor the Collateral Agent shall be under any duty
(a) to collect any of the Collateral or any moneys due or to become due
thereunder, (b) to give any notices with respect to the Collateral, (c) to
preserve or maintain any of the Collateral not in its possession, or (d) to
preserve rights of the Pledgor against prior parties to the Collateral. The
Agent and the Collateral Agent shall be deemed to have exercised reasonable
care with respect to any of the Collateral in their possession if the Agent or
the Collateral Agent takes such action for that purpose as the Pledgor shall
reasonably request in writing; provided, however, that no failure to comply
with any such request shall, of itself, be deemed a failure to exercise
reasonable care, and no failure to do any act not requested by the Pledgor
shall be deemed a failure to exercise reasonable care.

         5.       Pledgor's Representations and Warranties and Covenants.  The
Pledgor represents and warrants and covenants that:

         (i)      it has received value (as defined in Section 1-201 (44) of
                  the Maryland Uniform Commercial Code),

         (ii)     it has the right to create a security interest in the
                  Collateral,

         (iii)    the Collateral is not subject to the interest of any third
                  person,

         (iv)     the Pledgor will defend the Collateral against the claims
                  and demands of all third parties,

         (v)      all statements provided by Pledgor relating to the
                  Collateral relied upon by the Agent prior to,
                  contemporaneous with or subsequent to execution of this
                  Agreement are or shall be true, correct, complete, valid and
                  genuine in all material respects,

         (vi)     it has taken or caused other persons to take all actions
                  necessary to effect the creation and perfection of the
                  Agent's security interest in the Collateral, and has caused
                  to be filed with the Maryland State Department of
                  Assessments and Taxation, the Secretary of State of the
                  jurisdiction of organization of the Pledgor, and, if the
                  Account is maintained in a different jurisdiction, the
                  Secretary of State of the jurisdiction in which the Account
                  is maintained, UCC-1 financing statements naming the Pledgor
                  as debtor and the Agent as a secured party and evidencing
                  the lien or pledge created by this Agreement, and, together
                  with the book entries described above, such actions taken
                  with respect to the Collateral pursuant to this Agreement
                  create a valid and perfected first priority security
                  interest in the Collateral, pursuant to the Maryland Uniform
                  Commercial Code,

                                      3

<PAGE>

         (vii)    it has full power, authority and legal right to enter into
                  this Agreement and to pledge and grant a lien on the
                  Collateral pursuant to this Agreement, and this Agreement
                  has been duly authorized, executed and delivered by Pledgor
                  and constitutes the legal, valid and binding obligation of
                  Pledgor, enforceable against Pledgor in accordance with its
                  terms,

         (viii)   no authorization, consent, approval, license, qualification
                  or formal exemption from, nor any filing, declaration or
                  registration with, any court, governmental authority, or
                  with any securities exchange is required in connection with
                  (A) the due execution, delivery or performance by Pledgor of
                  this Agreement, (B) the assignment of, and the grant of a
                  lien on (including priority thereof), the Collateral by
                  Pledgor in the manner and for the purpose contemplated by
                  this Agreement, or (C) the exercise of the rights and
                  remedies of Pledgee created hereby except those that have
                  been obtained or made concurrently with the execution
                  hereof, including, without limitation, filings in the
                  appropriate offices under the Maryland Uniform Commercial
                  Code,

         (ix)     Neither the execution and delivery of this Agreement, nor
                  the consummation of the transactions herein contemplated,
                  nor compliance with the terms and provisions hereof will
                  conflict with or result in a breach of, Pledgor's formation
                  agreements, any applicable law or regulation, or any order,
                  writ, injunction or decree of any court or governmental
                  authority binding on Pledgor, or any agreement or instrument
                  to which Pledgor is a party or by which Pledgor is bound or
                  to which any of the Collateral is subject, or result in the
                  creation or imposition of any lien upon Pledgor's earnings
                  or assets pursuant to the terms of any such agreement or
                  instrument,

         (x)      the pledge of the Collateral to the Agent is not done in
                  contemplation of insolvency or bankruptcy or with an intent
                  to hinder, delay or defraud any of Pledgor's creditors,

         (xi)     it is not insolvent immediately before signing this
                  Agreement and is not being rendered insolvent by the pledge
                  of the Collateral to Agent, and

         (xii)    it will not pledge, assign or grant a security interest in
                  the Collateral to any person other than the Pledgee.

         6.       Partial Release of Collateral. Provided no Event of Default
under this Agreement or any of the other Operative Documents has occurred and
is continuing, when the cash value of the Collateral (as set forth in
Paragraph 3 above) exceeds the Minimum Collateral Amount, the Pledgor shall
have the right to request that the Pledgee release from the security interest
granted pursuant to this Agreement Collateral in an amount equal to such
excess; provided, however, the Pledgor shall not have the right to request
such a release more than one time in any quarter.

         7.       Deposits to Account. If at any time the cash value of the
Collateral (as set forth in Paragraph 3 above) is less than the Minimum
Collateral Amount, the Pledgor shall within two (2) Business Days deposit to
the Account and designate on the records of the Collateral Agent as subject to
the security interest granted pursuant to this Agreement cash or marketable
securities in an amount equal to the difference, between (a) the Minimum
Collateral Amount, and (b) the market value of the Collateral. The Collateral
Agent shall notify the Pledgor in writing of the

                                      4

<PAGE>

amount to be deposited hereunder and the Pledgor shall promptly provide the
Agent with evidence reasonably satisfactory to the Agent that such deposit has
been made.

         Other than with respect to reporting requirements regarding the
Collateral, the Collateral Agent shall have no obligations or responsibilities
hereunder to any parties hereto with respect to any accounts of the Pledgor
other than the Account. Notwithstanding the foregoing, however, nothing herein
provided shall abrogate the Collateral Agent's responsibilities to the Pledgor
with respect to any other accounts managed or held by the Collateral Agent for
or on behalf of the Pledgor.

         8.       Substitutions. Provided no Event of Default under this
Agreement or any of the other Operative Documents has occurred and is
continuing, the Pledgor may at any time and from time to time substitute cash
and marketable securities for the Collateral on deposit in the Account;
provided, however, the cash value of the Collateral (as set forth in Paragraph
3 above) shall at all times be equal to or greater than the Minimum Collateral
Amount.

         9.       Investment Earnings. Provided no Event of Default under this
Agreement or any of the other Operative Documents has occurred and is
continuing, when the cash value of the Collateral (as set forth in Paragraph 3
above) equals at least Minimum Collateral Amount, investment earnings on the
Collateral shall, on the last day of each quarter thereafter, be distributed
to the Pledgor.

         10.      Reporting Requirements. Not more than five (5) Business Days
following the end of each calendar month, the Collateral Agent shall furnish
to the Agent and the Pledgor a statement of the market value of the Collateral
on deposit in the Account.

         11.      Authority Over Account; Limitations on Withdrawals. The
Agent shall have sole authority over withdrawals of the Collateral from the
Account and no withdrawal of the Collateral from the Account shall be made
except upon the written instructions of the Agent signed by authorized
officers of the Agent; provided, however, such withdrawals shall only be
permitted when there is an Event of Default pursuant to this Agreement or any
of the other Operative Documents or when the Agent is releasing excess funds
pursuant to Paragraphs 6, 8 or 9 hereof. Any written instructions from the
Agent shall permit withdrawals within two (2) Business Days from the date
thereof. In relying upon such written instructions from the Agent, the
Collateral Agent shall have no liability other than for its negligence or
willful misconduct.

         12.      Default; Remedies Upon Default. The occurrence of any one or
more of the following events shall constitute an Event of Default under this
Agreement: (a) an event of default under the Facility Lease or under any of
the other Operative Documents after giving effect to any notice and cure
periods provided for in the Facility Lease or other Operative Documents; or
(b) failure of the Pledgor to perform, observe, or comply with any of the
provisions of this Agreement, and such failure shall remain uncured for a
period of five (5) days in the event of a monetary default and thirty (30)
days in the event of a non-monetary default after the date of written notice
from a Pledgee to the Pledgor. The Agent shall give the Collateral Agent and
the Pledgor written notice of an Event of Default hereunder and the Collateral
Agent shall from receipt of such notice act only upon the instructions of the
Agent and the Collateral Agent shall have no liability to the Pledgor in
following such instructions.

                                      5

<PAGE>

         Upon an Event of Default under this Agreement or under any of the
other Operative Documents that has not been waived by the Agent, and any time
thereafter, the Agent may, among its other rights and remedies (1) cause the
Collateral to be transferred to the Bank or to the name of its nominee or
nominees and thereafter exercise as to the Collateral all rights, powers and
remedies of an owner, (2) collect by legal proceedings or otherwise all
dividends, interest, principal payments, and other sums now or hereafter
payable on account of the Collateral, and hold the same as Collateral, or
apply the same to the expenses incurred by the Agent in such legal
proceedings, the manner and distribution of the application to be in the sole
discretion of the Agent, (3) enter into any extension, subordination,
reorganization, deposit, merger, or consolidation agreement, or any other
agreement relating to or affecting the Collateral and in connection therewith
deposit or surrender control of such Collateral thereunder, and accept other
property in exchange therefor and hold or apply such property or money so
received in accordance with the provisions hereof, all of the foregoing
specified rights and remedies, however, being subject to the rights of the
Pledgor provided in the Maryland Uniform Commercial Code. The Agent shall give
written notice to the Pledgor ten (10) days prior to the date of public sale
of the Collateral or prior to the date after which private sale of the
Collateral will be made.

         Subject to compliance with federal and state securities laws, full
power and authority are hereby given to the Agent acting through any of its
respective officers, upon an Event of Default hereunder or under any of the
other Operative Documents that has not been waived by the Agent, and at any
time thereafter, at its election, to sell, assign, transfer and deliver the
whole of the Collateral, or any part thereof or any additions thereto, or
substitutes therefor, in such order as the Agent may elect, at public or
private sale.

         To the extent the Agent actually receives any monies as a result of
its exercise of any of the remedies provided for hereunder following the
occurrence of an Event of Default hereunder or under any of the other
Operative Documents, the Agent covenants and agrees that such monies, after
deducting all costs incurred by the Agent in connection with the collection
thereof, shall be credited against the obligations of the Pledgor under the
Facility Lease and the Letter of Credit Agreement, including without
limitation, any payment obligation of the Pledgor pursuant to Paragraph 19 of
the Facility Lease.

         No failure or delay by the Agent to insist upon the strict
performance of any term, condition, covenant, or agreement of this Agreement
or any of the other Operative Documents, or to exercise any right, power, or
remedy consequent upon a breach thereof, shall constitute a waiver of any such
term, condition, covenant, or amendment or of any such breach, or preclude the
Agent from exercising any such right, power, or remedy at any later time or
times. By accepting payment after the due date of any of the obligations under
this Agreement or of the Facility Lease or any of the other Operative
Documents, the Agent shall not be defined to have waived the right either to
require prompt payment when due of all other such obligations or to declare a
default for failure to effect such payment of any such other obligations.

         Each right, power, and remedy of the Agent as provided for in this
Agreement or in the Facility Lease or any of the other Operative Documents or
now or hereafter existing at law or in equity or by statute or otherwise shall
be cumulative and concurrent and shall be in addition to every other right,
power, or remedy provided for in this Agreement or in the Facility or any of

                                      6

<PAGE>

the other Operative Documents or now or hereafter existing at law or in equity
or by statute or otherwise, and the exercise or beginning of the exercise by
the Agent of any one or more of such rights, powers, or remedies shall not
preclude the simultaneous or later exercise by the Agent of any or all such
other rights, powers, or remedies.

         13.      Costs and Expenses. All reasonable costs and expenses,
including reasonable attorney's fees and expenses, incurred or paid by the
Agent in exercising any right, power or remedy conferred hereby, and in the
endorsements thereof, shall become a part of the indebtedness or obligations
secured hereby.

         14.      Further Assurances.  The Pledgor shall, at its expense, do,
make, procure, execute and deliver all acts, things, writings and assurances
as any Pledgee may at any time request to protect, assure or enforce its
interest, rights and remedies created by, provided in or emanating from this
Agreement.

         15.      Release, Indulgences, etc. The Pledgor agrees that demands,
notice, protest and all demands and notices of any action taken by any Pledgee
under this Agreement, except those expressly provided for in this Agreement
and the Facility Lease, are hereby waived. Without notice to and further
consent from the Pledgor, without in any way waiving any of the provisions of
this Agreement, and without in any way releasing all or any part of the
Pledgor's obligations under this Agreement or in the Collateral, the Pledgor
hereby consents: (a) to any renewal, modification, waiver, or release of, any
of the obligations of the Agent under any of the Operative Documents; (b) to
the addition to, or release of any party or of any other maker, accommodation
party, endorser, guarantor, surety, or indemnitor from, any of their
respective obligations under any of the Operative Documents; (c) to the
addition to, or release of, all or any part of the collateral and security for
the Lease or any of the Operative Documents (other than the Collateral); (d)
to any indulgence and/or waiver given to any maker, accommodation party,
endorser, guarantor, surety, or indemnity of any of the obligations of the
Pledgor under the Lease or any of the Operative Documents.

         16.      Liability, Duties, and Resignation of Collateral Agent.

                  (a)      The Collateral Agent shall hold the Collateral as
agent for the Agent. The Collateral Agent agrees to send a written
confirmation to the Agent that it is holding the Collateral and the Account
for the sole and exclusive account of the Agent for the benefit of Agent.

                  (b)      The Collateral Agent, its affiliates, directors and
officers and its respective successors, assigns, agents and servants, absent
negligence or willful misconduct, shall not be held to any personal liability
whatsoever, in tort, contract or otherwise, in connection with the execution
and delivery of, or performance of its obligations under, this Agreement.

                  (c)      This Agreement sets forth exclusively the duties of
the Collateral Agent with respect to any and all matters pertinent hereto and
no implied duties or obligations shall be read into this Agreement against the
Collateral Agent. The Collateral Agent may act in reliance upon any instrument
or signature believed by it to be genuine and may assume that any person

                                      7

<PAGE>

purporting to give any writing, notice, advice or direction for or on behalf
of the Agent in connection with the provisions hereof has been duly authorized
to do so.

                  (d)      The Collateral Agent may resign from its
obligations under this Agreement at any time after thirty (30) days' prior
written notice to the other parties hereto, but in no event shall Collateral
Agent be released of its obligations hereunder unless and until a substitute
eligible institution has been designated and has assumed in writing the
obligations of Collateral Agent hereunder.

         17.      Notices. All notices, demands, requests, consents,
approvals, certificate or other communications required under this Agreement
to be in writing shall be sufficiently given and shall be deemed to have been
properly given (i) if delivered by hand, when written confirmation of delivery
is received by the sender, (ii) three days after the same is mailed by
certified mail, postage prepaid, return receipt requested, or (iii) if sent by
overnight courier, 24 hours after delivery to such overnight courier,
addressed to the person to whom any such notice, demand, request, approval,
certificate or other communication is to be given, at the appropriate address
of such person as designated below:

If to the Pledgor at:        Human Genome Sciences, Inc.
                             9410 Key West Avenue
                             Rockville, Maryland 20850
                             Attention:       Steven C. Mayer
                                              Senior Vice President and CFO
                             Tel: (301) 340-3444
                             Fax: (301) 309-0092

                             and

                             Human Genome Sciences, Inc.
                             9410 Key West Avenue
                             Rockville, Maryland  20850
                             Attention:       James H. Davis. Esquire
                                              Senior Vice President
                                              and General Counsel
                             Tel: (301) 251-6039
                             Fax: (301) 517-8831

If to the Agent at:          Allfirst Bank
                             6303 Ivy Lane, Suite 200
                             Greenbelt, Maryland 20770
                             Attention:    Joseph C. LeMense
                                           Senior Vice President
                             Tel:          (301) 397-5057
                             Fax:          (301) 397-5666

                                      8

<PAGE>

If to the Collateral         Allfirst Trust Company National Association
Agent at:                    25 South Charles Street
                             Baltimore, Maryland 21201
                             Attention: Jay Smith
                             Tel: (410) 244-4223
                             Fax: (410) 244-4256

         18.      Miscellaneous. Neither this Agreement nor any term,
condition, covenant, or agreement hereof may be changed, waived, discharged,
or terminated orally, but only by an instrument in writing signed by the party
against whom enforcement of the change, waiver, discharge, or termination is
sought. This Agreement shall be governed by the laws of the State of Maryland
and shall be binding upon the successors and assigns of the Pledgor and shall
inure to the benefit of the Agent and its respective successors and assigns.
As used herein, the singular number shall include the plural, and the use of
the masculine, feminine, or neuter gender shall include all genders as the
context may require, and the term "person" shall include an individual, a
corporation, an association, a partnership, a trust, a limited liability
company, an organization, a government or political subdivision thereof, and a
governmental agency. Headings and captions used in this Agreement are solely
for convenience of reference and shall not affect the meaning of this
Agreement. Unless varied by this Agreement, all terms used herein which are
defined by the Maryland Uniform Commercial Code shall have the same rneanings
hereunder as assigned to them by the Maryland Uniform Commercial Code. This
Agreement may be executed in several counterparts, each of which shall be an
original and all of which shall constitute one and the same

         19.      Termination. This Agreement shall terminate when the Letter
of Credit Agreement terminates and all obligations thereunder and under the
other Operative Documents have been indefeasibly paid and performed in full,
and upon the termination of this Agreement, the Agent shall instruct the
Collateral Agent to reassign to the Pledgor, without recourse or warranty,
express or implied, the then existing rights, title and interest of the Agent
in and to the Collateral, the costs of such reassignment to be borne by the
Pledgor.

                    (SIGNATURES APPEAR ON FOLLOWING PAGE)

                                      9

<PAGE>

         WITNESS the signature and seal of the Parties as of the date first
written above.

WITNESS:                          HUMAN GENOME SCIENCES, INC.,
                                    as Pledgor

                                  By:  /s/ STEVEN C. MAYER          (SEAL)
------------------------             -------------------------------
                                       Steven C. Mayer
                                       Chief Financial Officer

WITNESS:                          ALLFIRST BANK,
                                    as Agent

                                  By: /s/ JOSEPH C. LEMENSE         (SEAL)
-----------------------              -------------------------------
                                  Name:   Joseph C. Lemense
                                       -----------------------------
                                  Title:  Senior Vice President
                                        ----------------------------

WITNESS:                          ALLFIRST TRUST COMPANY NATIONAL ASSOCIATION,
                                    as Collateral Agent

                                  By: /s/ C.D. PARKER               (SEAL)
-----------------------              -------------------------------
                                  Name:   C.D. Parker
                                       -----------------------------
                                  Title:  Vice President
                                        ----------------------------

                                      10
<PAGE>

                                      11

<PAGE>

                                                                   Exhibit A to
                                               Cash Collateral Pledge Agreement

                            DESCRIPTION OF ACCOUNT

<TABLE>
<CAPTION>
Account Owner              Account Name                       Account Number
-------------              ------------                       --------------
<S>                        <C>                                <C>
Human Genome               Human Genome Sciences,
Sciences, Inc.             Inc. 2001 Collateral Account          --------
</TABLE>

                                      12

<PAGE>

                                                                   Exhibit B to
                                               Cash Collateral Pledge Agreement

                            PERMITTED INVESTMENTS

         The term "Permitted Investments" as used in this Cash Collateral
Pledge Agreement means any of the following:

         Any investments allowed under the investment guidelines approved by
the board of directors of the Pledgor, provided that such investments shall
meet the following limitations:

         Such investments shall be direct obligations of the United States of
America or other obligations the timely payment of the principal of and
interest on which are fully and unconditionally guaranteed by the United
States of America or debt securities rated "A-" or better by Standard & Poor's
Ratings Services or "Aa3" or better by Moody's Investors Service, Inc,
provided that (i) no more than ten percent (10%) of the Collateral shall be
invested at any time in the obligations of any one corporate issuer, (ii) no
such obligation shall have a maturity in excess of seven (7) years, and (iii)
such obligations shall not have an average duration exceeding seven (7) years.

                                      13<PAGE>

                                                                  EXHIBIT 10.24

                                  GUARANTEE

                                      by

                         HUMAN GENOME SCIENCES, INC.,
                                as Guarantor,

                                 in favor of

                                ALLFIRST BANK,
                                   as Agent

                         Dated as of October 25, 2001

               ------------------------------------------------

<PAGE>

                                  GUARANTEE

         THIS GUARANTEE, dated as of October 25, 2001 (this "Guarantee"), is
made by HUMAN GENOME SCIENCES, INC., a Delaware corporation (in its capacity
as guarantor hereunder, "Guarantor") in favor of ALLFIRST BANK, a Maryland
banking corporation (in its capacity as agent hereunder, the "Agent").

                             W I T N E S S E T H:

         WHEREAS, in accordance with the provisions of Article 83A, Title 5,
Subtitle 2 of the Annotated Code of Maryland, as amended, and pursuant to a
certain Trust Indenture dated as of October 25, 2001 (the "Indenture") between
Maryland Economic Development Corporation (the "Issuer") and Allfirst Trust
Company National Association, as Trustee (the "Trustee"), the Issuer has
issued $73,000,000 in principal amount of its Taxable Variable Rate Demand
Revenue Bonds (Human Genome Sciences, Inc. Facility), Series 2001 A (the
"Bonds") to refinance a portion of the acquisition cost of certain improved
real property located at 9800 Medical Center Drive, Rockville, Maryland (the
"Property") and to finance a portion of the cost associated with the
construction of the Additional Improvements (as defined in the Facility Lease)
on the Property;

         WHEREAS, in order to enhance the marketability of the Bonds and
pursuant to a Letter of Credit Agreement dated as of October 25, 2001 (the
"Letter of Credit Agreement") between the Issuer and Allfirst Bank (in its
capacity as Letter of Credit issuer and Certificate Holder, the "Bank"), the
Bank has issued to the Trustee the Bank's irrevocable transferable letter of
credit to provide payment for and secure the payment of the principal of and
interest on, and the purchase price of, the Bonds;

         WHEREAS, simultaneously with the issuance of the Bonds and pursuant
to a Trust Agreement dated as of October 25, 2001 (the "Trust Agreement")
between the Bank, as Holder, and Wells Fargo Bank Northwest, National
Association, as Owner Trustee (the "Owner Trustee"), the Bank has advanced
funds for the purchase from the HGSI Trust 2001-B of up to $3,000,000 in
principal amount of HGSI Trust 2001-B Certificates (the "Certificates");

         WHEREAS, the Issuer may enter into from time to time a Hedge
Agreement with the Hedge Counterparty (in each case, as defined in the Lease
Agreement dated as of October 25, 2001 between the Owner Trustee on behalf of
the Trust, as Lessor, and the Guarantor, as Lessee (as supplemented, the
"Facility Lease"));

         WHEREAS, it is a condition precedent to the consummation by the Bank
of the transactions to be consummated by the Operative Documents (as defined
in the Facility Lease) that Guarantor execute and deliver this Guarantee;

         WHEREAS, it is in the best interests of Guarantor that the
transactions contemplated by the Operative Documents occur;

<PAGE>

         WHEREAS, Guarantor has reviewed and approved the Operative Documents
and is fully informed of (a) the extent of the Bank's obligations thereunder
and (b) the remedies the Bank, or the Agent on the Bank's behalf, may pursue
thereunder, with or without notice to Guarantor; and

         WHEREAS, this Guarantee, and the execution, delivery and performance
hereof, have been duly authorized by all necessary corporate action of
Guarantor;

         NOW, THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt of which is hereby acknowledged by
Guarantor, Guarantor hereby agrees as follows:

         Section 1.        Guarantee. Guarantor hereby irrevocably and
unconditionally guarantees to the Agent, for the benefit of the Bank and the
Hedge Counterparty, and their respective successors and permitted assigns
(individually a "Beneficiary" and collectively 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, 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 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 Guaranty.

         In any action or proceeding involving any state corporate law, or any
state or federal or any other bankruptcy, insolvency, reorganization or any
other law affecting the rights of creditors generally, if the obligations of
Guarantor under this Guarantee would otherwise be held

                                     -2-

<PAGE>

or determined to be void, invalid or unenforceable, or subordinated to the
claims of any other creditors, on account of the amount of its liability under
this Guarantee, then, notwithstanding any other provision hereof to the
contrary, the amount of such liability shall, without any further action by
Guarantor or any other Person, be automatically limited and reduced to the
highest amount which is valid and enforceable as determined in such action or
proceeding.

         This Guarantee shall in all respects constitute an absolute and
unconditional guaranty of payment and performance (and not of collection), and
shall remain in full force and effect until the full and indefeasible payment
and performance of all of the Liabilities and all of the Guarantor's
obligations hereunder (notwithstanding, without limitation, the dissolution of
Guarantor). The liability of Guarantor hereunder may be enforced without the
Beneficiaries being required to resort to any other right, remedy or security.

         The obligations of Guarantor are independent of any obligations under
any of the Operative Documents. Each and every default under any of the
Operative Documents shall give rise to a separate claim and cause of action
hereunder, and separate claims or suits may be made and brought, as the case
may be, hereunder as each such default occurs.

         Agent, on behalf of itself and the Beneficiaries, and the
Beneficiaries each may, from time to time at its discretion and without notice
to Guarantor, but subject to the provisions of the Facility Lease, take any or
all of the following actions: (a) retain or obtain a lien upon or a security
interest in any property to secure any of the Liabilities or any obligation
hereunder; (b) retain or obtain the primary or secondary obligation of any
obligor or obligors, in addition to Guarantor, with respect to any of the
Liabilities; (c) extend or renew for one or more periods (regardless of
whether longer than the original period), alter or exchange any of the
Liabilities, or release or compromise any obligation of Guarantor hereunder or
any obligation of any nature of any other obligor with respect to any of the
Liabilities; (d) release or fail to perfect its lien upon or security interest
in, or impair, surrender, release or permit any substitution or exchange for,
all or any part of any property securing any of the Liabilities or any
obligation hereunder, or extend or renew for one or more periods (regardless
of whether longer than the original period) or release, compromise, alter or
exchange any obligations of any nature of any obligor with respect to any such
property; and (e) resort to Guarantor for payment of any of the Liabilities,
regardless of whether Agent or any other Person shall have resorted to any
other Person or to any property securing any of the Liabilities or any
obligation hereunder or shall have proceeded against any other obligor
primarily or secondarily obligated with respect to any of the Liabilities (all
of the actions referred to in this paragraph being hereby expressly waived by
Guarantor).

         Section 2.        Guarantor's Obligations Unconditional. Guarantor's
obligations hereunder are independent of the obligations of the Issuer, the
Trust or any other Person under the Operative Documents, and each Beneficiary
may enforce any of its rights hereunder independently of any other right or
remedy that it may at any time hold with respect to the Liabilities or any
security or other guaranty therefor. Such obligations shall be absolute and
unconditional, shall not be subject to any counterclaim, setoff, deduction,
diminution, abatement, recoupment, suspension, deferment, reduction or defense
(other than full and indefeasible payment and performance of all of the
Liabilities and full and strict compliance by Guarantor with its obligations
hereunder), whether based upon any claim that the Issuer, the Trust,

                                     -3-

<PAGE>

Guarantor or any other Person may have against any Beneficiary or any other
Person or otherwise, and shall remain in full force and effect without regard
to, and shall not be released, discharged or in any way affected by, any
circumstance or condition whatsoever (whether or not Guarantor or any other
Person shall have any knowledge or notice thereof) including, without
limitation:

                  (A)      any amendment, modification, addition, deletion,
         supplement or renewal to or of or other change in the Liabilities or
         any Operative Document or any of the agreements referred to in any
         thereof, or any other instrument or agreement applicable to any
         Operative Document or any of the parties to such agreements, or to
         the Property, or any assignment, mortgage, encumbrance or transfer
         thereof or of any interest therein, or any furnishing or acceptance
         of additional security for, guaranty of or right of offset with
         respect to, any of the Liabilities; or the failure of any security or
         the failure of any Beneficiary or any other Person to perfect or
         insure any interest in any collateral;

                  (B)      any failure, impossibility, illegality, omission or
         delay on the part of the Agent, any Beneficiary or any other Person
         to conform or comply with any term of any instrument or agreement
         referred to in clause (A) above;

                  (C)      any waiver, consent, extension, indulgence,
         compromise, release or other action or inaction under or in respect
         of any instrument, agreement, guaranty, right of offset or security
         referred to in clause (A) above or any obligation or liability of the
         Agent, any Beneficiary or any other Person, or any exercise or
         non-exercise by the Agent, any Beneficiary or any other Person of any
         right, remedy, power or privilege under or in respect of any such
         instrument, agreement, guaranty, right of offset or security or any
         such obligation or liability;

                  (D)      any bankruptcy, insolvency, reorganization,
         arrangement, readjustment, composition, liquidation or similar
         proceeding with respect to the Issuer, the Trust, any Beneficiary or
         any other Person or any of their respective properties or creditors,
         or any action taken by any trustee, receiver or court in any such
         proceeding;

                  (E)      any limitation on the liability or obligations of
         any Person under any Operative Document, the Liabilities, any
         collateral security for the Liabilities, any other guaranty of the
         Liabilities or any discharge, termination, cancellation, frustration,
         irregularity, invalidity or unenforceability, in whole or in part, of
         any of the foregoing or any other agreement, instrument, guaranty or
         security referred to in clause (A) above or any term of any thereof;

                  (F)      any defect in the title, compliance with
         specifications, condition, design, operation or fitness for use of,
         or any damage to or loss or destruction of, or any interruption or
         cessation in the use of the Property or any portion thereof by
         Guarantor or any other Person for any reason whatsoever (including,
         without limitation, any governmental prohibition or restriction,
         condemnation, requisition, seizure or any other act on the part of
         any governmental or military authority, or any act of God or of the
         public enemy) regardless of the duration thereof (even though such
         duration would

                                     -4-

<PAGE>

         otherwise constitute a frustration of a lease), whether or not
         resulting from accident and whether or not without fault on the part
         of Guarantor or any other Person;

                  (G)      any merger or consolidation of Guarantor into or
         with any other Person, or any sale, lease or transfer of any of the
         assets of Guarantor to any other Person;

                  (H)      any change in the ownership of any shares of
         capital stock of Guarantor or any corporate change in Guarantor;

                  (I)      any loan to or other transaction between any of the
         Beneficiaries or any other Person and Guarantor;

                  (J)      any recovery of judgment against the Issuer, the
         Trust, or the Guarantor by any levy of any writ or process of
         execution under any such judgment;

                  (K)      absence of any notice to, or knowledge of,
         Guarantor of the existence or occurrence of any of the foregoing
         clauses (A) through (J); or

                  (L)      any other occurrence or circumstance whatsoever
         (other than full and indefeasible payment and performance of all of
         the Liabilities and all of Guarantor's obligations hereunder),
         whether similar or dissimilar to the foregoing, and any other
         circumstance that might otherwise constitute a legal or equitable
         defense or discharge of the liabilities of a guarantor or surety or
         that might otherwise limit recourse against Guarantor.

         The obligations of Guarantor set forth herein constitute the full
recourse obligations of Guarantor enforceable against it to the full extent of
all its assets and properties, notwithstanding any provision in any Operative
Document or any other document or agreement to the contrary.

         Guarantor waives any and all notice of the creation, renewal,
extension or accrual of any of the Liabilities and notice of or proof of
reliance by the Agent, any Beneficiary or any other Person upon this Guarantee
or acceptance of this Guarantee, and the Liabilities, and any of them, shall
conclusively be deemed to have been created, contracted or incurred in
reliance upon this Guarantee. Guarantor unconditionally waives, to the extent
permitted by law: (a) acceptance of this Guarantee and proof of reliance by
any Beneficiary or any other Person hereon; (b) notice of any of the matters
referred to in clauses (A) through (I) above, or any right to consent or
assent to any thereof; (c) all notices that may be required by statute, rule
of law or otherwise, now or hereafter in effect, to preserve intact any rights
against Guarantor, including, without limitation, any demand, presentment,
protest, proof or notice of nonpayment under any Operative Document, and
notice of default or any failure on the part of and Person to perform and
comply with any covenant, agreement, term or condition of any Operative
Document; (d) any right to the enforcement, assertion or exercise against the
Issuer or the Trust of any right, power, privilege or remedy conferred in any
Operative Document or otherwise; (e) any requirement of diligence on the part
of any Person; (f) any requirement of any Beneficiary or any other Person to
take any action whatsoever, to exhaust any remedies, proceed first against the
Issuer or the Trust or to mitigate the damages resulting from a default by any
Person under any Operative Document; (g)

                                     -5-

<PAGE>

any notice of any sale, transfer or other disposition by any Person of any
right under, title to or interest in any Operative Document or the Property;
and (h) any other circumstance whatsoever that might otherwise constitute a
legal or equitable discharge, release or defense of a guarantor or surety, or
that might otherwise limit recourse against Guarantor.

         Guarantor agrees that this Guarantee shall be automatically
reinstated if and to the extent that for any reason any payment by or on
behalf of itself, the Issuer or the Trust is rescinded or must be otherwise
restored by any Beneficiary, whether as a result of any proceedings in
bankruptcy or reorganization or otherwise.

         Guarantor further agrees that, without limiting the generality of
this Guarantee, if any default under any Operative Document shall have
occurred and be continuing and any Beneficiary is prevented by applicable law
from exercising its remedies under the Operative Documents, such Beneficiary
shall be entitled to receive hereunder from Guarantor, upon demand therefor,
the sums which would have otherwise been due had such remedies been exercised.

         In addition, Guarantor assumes the responsibility for being and
keeping itself informed of the financial condition of the Issuer and the Trust
and of all the circumstances bearing upon the risk of nonpayment of the
Liabilities that diligent inquiry would reveal, and that absent a request for
such information by Guarantor, the Beneficiaries shall have no duty to advise
Guarantor of information known to them regarding such condition any such
circumstance.

         Section 3.        Waivers.

                  (a)      Guarantor hereby irrevocably waives any claim or
other rights which it may now or hereafter acquire against the Issuer or the
Trust arising from the existence, payment, performance or enforcement of such
Guarantor's obligations under this Guarantee or any other Operative Document,
including any right of subrogation, reimbursement, contribution, exoneration,
or indemnification, any right to participate in any claim or remedy of any
Beneficiary against the Issuer or the Trust or any property or assets now or
hereafter constituting part of the Owner Trust Estate (as defined in the Trust
Agreement), whether or not such claim, remedy or right arises in equity, or
under contract, statute or common law. If any amount shall be paid to
Guarantor in violation of the preceding sentence and the Liabilities shall not
have been indefeasibly paid in cash, such amount shall be deemed to have been
paid to Guarantor for the benefit of, and held in trust for, the
Beneficiaries, and shall forthwith be paid to the Agent to be credited and
applied pursuant to the terms of the Operative Documents. Guarantor
acknowledges that it will receive direct and indirect benefits from the
financing arrangements contemplated by the Operative Documents and that the
waiver set forth in this paragraph is knowingly made in contemplation of such
benefits.

                  (b)      Guarantor hereby absolutely, unconditionally and
irrevocably waives and agrees not to assert or take advantage of any defense
based upon an election of remedies by Owner Trustee, Agent or any other
Beneficiary or other Person.

                                     -6-

<PAGE>

                  (c)      Guarantor hereby waives all rights and defenses
that the Guarantor may have because any of the Liabilities is secured by real
property. This means, among other things:

                           (i)      the Beneficiaries may collect from
                   Guarantor without first foreclosing on any real or personal
                   property collateral pledged by the Issuer or the Trust;

                           (ii)     if the Beneficiaries foreclose on any real
                  property collateral pledged with respect to the Liabilities:
                  (A) the amount of the Liabilities may be reduced only by the
                  price for which that collateral is sold at the foreclosure
                  sale, even if the collateral is worth more than the sale
                  price; (B) the Beneficiaries may collect from Guarantor even
                  if the Beneficiaries, by foreclosing on the real property
                  collateral, have destroyed any right Guarantor may have to
                  collect from the Issuer or the Trust. This is an
                  unconditional and irrevocable waiver of any rights and
                  defenses Guarantor may have because the Liabilities are
                  secured by real property.

         (d)      Guarantor hereby waives the pleading of any statute of
limitation as a defense to its obligations hereunder.

         Section 4.        Reasonableness and Effect of Waivers. Guarantor
warrants and agrees that each of the waivers set forth in this Guarantee is
made with full knowledge of its significance and consequences and that, under
the circumstances, the waivers are reasonable and not contrary to public
policy or law. If any of such waivers are determined to be contrary to any
applicable law or public policy, such waivers shall be effective only to the
maximum extent permitted by law.

         Section 5.        Transfers by Beneficiaries. Each Beneficiary may,
from time to time, whether before or after any discontinuance of this
Guarantee, at its sole discretion and without notice to Guarantor, assign or
transfer any or all of its portion of the Liabilities or any interest therein
in accordance with the terms and conditions of the Operative Documents; and,
notwithstanding any such assignment or transfer or any subsequent assignment
or transfer thereof, such Liabilities shall be and remain Liabilities for the
purposes of this Guarantee, and each and every immediate and successive
assignee or transferee of any of the Liabilities or of any interest therein
shall, to the extent of such assignee's or transferee's interest in the
Liabilities, be entitled to the benefits of this Guarantee to the same extent
as if such assignee or transferee were such Beneficiary.

         Section 6.        No Waiver by Beneficiaries. No delay in the
exercise of any right or remedy shall operate as a waiver thereof, and no
single or partial exercise of any right or remedy shall preclude other or
further exercise thereof or the exercise of any other right or remedy; nor
shall any modification or waiver of any of the provisions of this Guarantee be
binding upon any Beneficiary except as expressly set forth in a writing duly
signed and delivered on its behalf. No action permitted hereunder shall in any
way affect or impair any Beneficiary's rights or Guarantor's obligations under
this Guarantee. For the purposes of this Guarantee, Liabilities shall include
all of the obligations described in the definition thereof, notwithstanding
any right

                                     -7-

<PAGE>

or power of Guarantor or anyone else to assert any claim or defense as to the
invalidity or unenforceability of any such obligation, and no such claim or
defense shall affect or impair the obligations of Guarantor hereunder.
Guarantor's obligations under this Guarantee shall be absolute and
unconditional irrespective of any circumstance whatsoever which might
constitute a legal or equitable discharge or defense of Guarantor other than
proof of indefeasible satisfaction or indefeasible payment in full of the
Liabilities guaranteed hereunder. Guarantor hereby acknowledges that there are
no conditions to the effectiveness of this Guarantee.

         Section 7.        Successors and Assigns. This Guarantee shall be
binding upon Guarantor and upon Guarantor's successors and assigns; and all
references herein to Guarantor shall be deemed to include any successor or
successors, whether immediate or remote, to such Person.

         Section 8.        Severability. Wherever possible, each provision of
this Guarantee shall be interpreted in such manner as to be effective and
valid under all Law (as defined in the Facility Lease), but if any provision
of this Guarantee shall be prohibited by or invalid thereunder, such provision
shall be ineffective only to the extent of such prohibition or invalidity,
without invalidating the remainder of such provision or the remaining
provisions of this Guarantee.

         Section 9.        Notices. All notices, demands, requests, consents,
approvals, certificate or other communications required under this Agreement
to be in writing shall be sufficiently given and shall be deemed to have been
properly given (i) if delivered by hand, when written confirmation of delivery
is received by the sender, (ii) three days after the same is mailed by
certified mail, postage prepaid, return receipt requested, or (iii) if sent by
overnight courier, 24 hours after delivery to such overnight courier,
addressed to the person to whom any such notice, demand, request, approval,
certificate or other communication is to be given, at the appropriate address
of such person as designated below:

If to the Guarantor at:             Human Genome Sciences, Inc.
                                    9410 Key West Avenue
                                    Rockville, Maryland 20850
                                    Attention:       Steven C. Mayer
                                                     Senior Vice President
                                                     And CFO
                                    Tel: (301) 340-3444
                                    Fax: (301) 309-0092

                                    and

                                    Human Genome Sciences, Inc.
                                    9410 Key West Avenue
                                    Rockville, Maryland  20850
                                    Attention:       James H. Davis. Esquire
                                                     Senior Vice President
                                                     and General Counsel
                                    Tel: (301) 251-6039
                                    Fax: (301) 517-8831

                                     -8-

<PAGE>

If to the Agent at:                 Allfirst Bank
                                    6303 Ivy Lane, Suite 200
                                    Greenbelt, Maryland 20770
                                    Attention:    Joseph C. LeMense
                                                  Senior Vice President
                                    Tel:          (301) 397-5057
                                    Fax:          (301) 397-5666

         Section 10.       Governing Law. This Guarantee shall be governed by
the internal law of the State of Maryland as to all matters of construction,
validity and performance, without regard to conflicts of law principles.

         Section 11.       Submission to Jurisdiction. Guarantor hereto
irrevocably and unconditionally:

                  (a)      submits for itself and its property in any legal
         action or proceeding relating to this Guarantee or any other
         Operative Document, or for recognition and enforcement of any
         judgment in respect thereof, to the non-exclusive general
         jurisdiction of any federal or state court sitting in Montgomery
         County or Baltimore City, Maryland;

                  (b)      consents that any such action or proceedings may be
         brought to such courts, and waives any objection that it may now or
         hereafter have to the venue of any such action or proceeding in any
         such court or that such action or proceeding was brought in an
         inconvenient court and agrees not to plead or claim the same;

                  (c)      agrees that service of process in any such action
         or proceeding may be effected by mailing a copy thereof by registered
         or certified mail (or any substantially similar form of mail),
         postage prepaid, to such party at its address set forth above; and

                  (d)      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 to sue in any other jurisdiction.

         Section 12.       Jury Trial. GUARANTOR HEREBY IRREVOCABLY WAIVES ANY
AND ALL RIGHT TO A TRIAL BY JURY IN ANY ACTION OR PROCEEDING TO ENFORCE OR
DEFEND ANY RIGHTS UNDER THIS GUARANTEE OR ANY OTHER OPERATIVE DOCUMENT OR
UNDER ANY AMENDMENT, INSTRUMENT, DOCUMENT OR AGREEMENT DELIVERED OR WHICH MAY
IN THE FUTURE BE DELIVERED IN CONNECTION HEREWITH OR THEREWITH OR ARISING FROM
ANY RELATIONSHIP EXISTING IN CONNECTION WITH THIS GUARANTEE OR ANY OTHER
OPERATIVE DOCUMENT AND AGREES THAT ANY SUCH ACTION OR PROCEEDING SHALL BE
TRIED BEFORE A COURT AND NOT BEFORE A JURY.

                           [SIGNATURE PAGE FOLLOWS]

                                     -9-

<PAGE>

         IN WITNESS WHEREOF, Guarantor has caused this Guarantee to be
executed and delivered as of the date first above written.

WITNESS:                                    HUMAN GENOME SCIENCES, INC.,
                                                        as Pledgor

                                    By:   /s/ STEVEN C. MAYER             (SEAL)
------------------------               -----------------------------------
                                          Steven C. Mayer
                                          Senior Vice President and  Chief
                                          Financial Officer

                                     -10-

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