EXHIBIT 99.3 AGREEMENT TO FILE JOINTLY We, the undersigned, hereby express our agreement that the attached Schedule 13D is filed on behalf of each of us. AVENTIS PHARMACEUTICALS INC.

                                  EXHIBIT 99.3

                            AGREEMENT TO FILE JOINTLY

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


                                                AVENTIS PHARMACEUTICALS INC.



Date: January 7, 2002                           By:  /s/Xxxxxx X. Xxxxxxxxxxx
                                                     Xxxxxx X. Xxxxxxxxxxx
                                                     Vice President



                                                AVENTIS HOLDINGS INC.



Date: January 7, 2002                           By:  /s/Xxxxxxx X. Xxxxxxxx
                                                     Xxxxxxx X. Xxxxxxxx
                                                     President



                                                XXXXX-XXXXXXX XXXXX INC.



Date: January 7, 2002                           By:  /s/Xxxxxx X. Xxxxxxxxxxx
                                                     Xxxxxx X. Xxxxxxxxxxx
                                                     Vice President