11 EXHIBIT 99.D AGREEMENT TO FILE JOINTLY We, the undersigned, hereby express our agreement that the attached Schedule 13D is filed on behalf of each of us. HOECHST CORPORATION Date: March 21, 1996 By: /s/ David A Jenkins David A. Jenkins Vice...

                                                                11
                                  EXHIBIT 99.D

                           AGREEMENT TO FILE JOINTLY

     We, the undersigned, hereby express our agreement that the attached
Schedule 13D is filed on behalf of each of us.

                                        HOECHST CORPORATION



Date:  March 21, 1996                   By:  /s/ Xxxxx X Xxxxxxx
                                             Xxxxx X. Xxxxxxx
                                             Vice President, General
                                             Counsel and Secretary


                                        HOECHST XXXXXX XXXXXXX, INC.



Date:  March 21, 1996                   By:  /s/ Xxxxxxx X. Xxxxxxx
                                             Vice President,
                                             General Counsel, and
                                             Corporate Secretary