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                                 EXHIBIT 5.1







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6225 Smith Avenue
Baltimore, Maryland 21209-3600
www.piperrudnick.com

PHONE   (410) 580-3000
FAX     (410) 580-3001

                                 August 3, 2001

Human Genome Sciences, Inc.
9410 Key West Avenue
Rockville, Maryland 218050-3338

Ladies and Gentlemen:

        We have acted as counsel to Human Genome Sciences, Inc., a Delaware
Corporation (the "Company"), in connection with the preparation and filing
with the Securities and Exchange Commission of a registration statement on
Form S-8 (the "Registration Statement") registering 6,259,627 shares of Common
Stock, par value $.01 per share (the "Plan Shares"), issuable pursuant to the
exercise of stock options and other awards granted or to be granted under the
Company's Amended and Restated 2000 Stock Incentive Plan (the "Plan").

        We have examined copies of the Company's Restated Certificate of
Incorporation (as amended), By-Laws (as amended and restated), the Plan, all
resolutions adopted by the Company's Board of Directors relating to the above
and other records and documents that we have deemed necessary for the purpose
of this opinion. We have also examined such other documents, papers, statutes
and authorities as we have deemed necessary to form a basis for this opinion.
In our examination, we have assumed the genuineness of all signatures and the
conformity to original documents of all copies submitted to us. As to various
questions of fact material to this opinion, we have relied on statements and
certificates of officers and representatives of the Company and others.

        Based upon the foregoing, we are of the opinion that Plan Shares
issuable under the Plan have been duly authorized and will be (when issued,
sold and delivered as authorized) validly issued, fully paid and
non-assessable.

        The opinion set forth herein is limited to matters governed by the laws
of the State of Delaware and the Federal laws of the United States of America,
and we express no opinion as to any other laws.

        We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement.

                                            Very truly yours,

                                           /s/ PIPER MARBURY RUDNICK & WOLFE LLP