<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