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 9, 2002                      By:  /s/Xxxxxx X. Xxxxxxxxxxx
                                           Xxxxxx X. Xxxxxxxxxxx
                                           Vice President



                                           AVENTIS HOLDINGS INC.



Date: January 9, 2002                      By:  /s/Xxxxxxx X. Xxxxxxx
                                           Xxxxxxx X. Xxxxxxx
                                           President



                                           XXXXX-XXXXXXX XXXXX INC.



Date: January 9, 2002                      By:  /s/Xxxxxx X. Xxxxxxxxxxx
                                           Xxxxxx X. Xxxxxxxxxxx
                                           Vice President