EXHIBIT 3.1

                               AMENDMENT NO. 1 TO

          TRANSKARYOTIC THERAPIES, INC.'S AMENDED AND RESTATED BY-LAWS

Section 1 of Article III of Transkaryotic Therapies, Inc.'s Amended and Restated
By-Laws be and hereby is deleted in its entirety and the following is inserted
in lieu thereof:

                    "Section 1. Number and Qualifications: The number of
                    directors which shall constitute the whole Board of
                    Directors shall be determined by resolution of the Board of
                    Directors, but in no event shall be less than three (3) or
                    more than seven (7). The number of directors may be
                    increased at any time and from time to time by a majority of
                    the directors then in office. The number of directors may be
                    decreased at any time and from time to time by a majority of
                    the directors then in office, but only to eliminate
                    vacancies existing by reason of death, resignation, removal
                    or expiration of the term of one or more directors.
                    Directors need not be stockholders of the Corporation."