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                                                                    Exhibit 3.1

                            CERTIFICATE OF AMENDMENT
                                       TO
                  RESTATED CERTIFICATE OF INCORPORATION (FIFTH)
                                       OF
                           HUMAN GENOME SCIENCES, INC.

                             Pursuant to Section 242
                         of the General Corporation Law
                            of the State of Delaware

        Human Genome Sciences, Inc. (hereinafter called the "Corporation"),
organized and existing under and by virtue of the General Corporation Law of the
State of Delaware, does hereby certify as follows:

        FIRST: In accordance with the General Corporation Law of the State of
Delaware, the Board of Directors of the Corporation adopted resolutions pursuant
to Section 242 of the General Corporation Law of the State of Delaware setting
forth an amendment to the Restated Certificate of Incorporation (Fifth) of the
Corporation and declaring said amendment to be advisable. The stockholders of
the Corporation duly approved said proposed amendment at an annual meeting in
accordance with Section 211 of the General Corporation Law of the State of
Delaware. The resolutions setting forth the amendment are as follows:

        RESOLVED: That Article III(a) of the Restated Certificate of
Incorporation (Fifth) be and hereby is amended by deleting the existing Article
III(a) and inserting the following paragraph in lieu thereof:

        "(a) Authorization. The total number of shares of all classes of stock
        which the Corporation shall have authority to issue is 420,000,000
        shares, consisting of 20,000,000 shares of Preferred Stock, par value
        $.01 per share (the "Preferred Stock"), and 400,000,000 shares of Common
        Stock, par value $.01 per share (the "Common Stock")."

        RESOLVED: That Article III(c)(1) of the Restated Certificate of
Incorporation (Fifth) be and hereby is amended by deleting the existing Article
III(c)(1) and inserting the following paragraph in lieu thereof:

        "(1) Designation and Amount. The designation of this class of capital
        stock shall be Common Stock, par value $.01 per share ("Common Stock").
        The number of shares, powers, terms, conditions, designations,
        preferences and privileges, relative, participating, optional and other
        special rights, and qualifications, limitations and restrictions, shall
        be as set forth in this Article III(c). The number of authorized shares
        of Common Stock is 400,000,000. The number of authorized shares of
        Common Stock may be increased or decreased (but not below the number of
        shares thereof then outstanding) by the affirmative vote of the holders
        of the majority of the stock of the Corporation entitled to



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        vote, irrespective of the provisions of section 242(b)(2) of the
        Delaware General Corporation Law."

        IN WITNESS WHEREOF, the Corporation has caused its corporate seal to be
affixed hereto and this Certificate of Amendment to be signed by its Chairman of
the Board and Chief Executive Officer this 23rd day of May, 2001.



[Corporate Seal]           HUMAN GENOME SCIENCES, INC.



                           By:  /s/ WILLIAM A. HASELTINE, PH.D.
                              -------------------------------------------
                              William A. Haseltine, Ph.D.
                              Chairman of the Board and Chief Executive Officer