JOINT FILING AGREEMENT

         EXHIBIT 1
         to SCHEDULE 13D



                             JOINT FILING AGREEMENT

                  Each of the undersigned hereby acknowledges and agrees, in
compliance with the provisions of Rule 13d-1(k)(1) promulgated under the
Securities Exchange Act of 1934, as amended, that the Schedule 13D to which this
Agreement is attached as an Exhibit (the "Schedule 13D"), and any amendments
thereto, will be filed with the Securities and Exchange Commission jointly on
behalf of the undersigned. This Agreement may be executed in one or more
counterparts.

Dated:  May 20, 2002


                                PERSEUS-XXXXX BIOPHARMACEUTICAL FUND, LP

                                By:     Perseus-Xxxxx Partners, LLC,
                                        General Partner

                                By:     SFM Participation, L.P.,
                                        Managing Member

                                By:     SFM AH, Inc.,
                                        General Partner

                                By:     /s/ Xxxxxxx X. Xxxxxxx, Xx.
                                        ---------------------------------------
                                        Name:   Xxxxxxx X. Xxxxxxx, Xx.
                                        Title:  Secretary


                                PERSEUS-XXXXX PARTNERS, LLC

                                By:     SFM Participation, L.P.
                                        Managing Member

                                By:     SFM AH, Inc.
                                        General Partner

                                By:     /s/ Xxxxxxx X. Xxxxxxx, Xx.
                                        ---------------------------------------
                                        Name:   Xxxxxxx X. Xxxxxxx, Xx.
                                        Title:  Secretary




                                PERSEUS BIOTECH FUND PARTNERS, LLC

                                By:     Perseuspur EC, L.L.C.
                                        Managing Member

                                By:     Perseuspur, LLC
                                        Member

                                By:     /s/ Xxxx Xxxxxxx
                                        ---------------------------------------
                                        Name:   Xxxx Xxxxxxx
                                        Title:  Secretary and Treasurer


                                PERSEUS EC, L.L.C.

                                By:     Perseuspur, LLC
                                        Member

                                By:     /s/ Xxxx Xxxxxxx
                                        ---------------------------------------
                                        Name:   Xxxx Xxxxxxx
                                        Title:  Secretary and Treasurer


                                PERSEUSPUR, LLC

                                By:     /s/ Xxxx Xxxxxxx
                                        ---------------------------------------
                                        Name:   Xxxx Xxxxxxx
                                        Title:  Secretary and Treasurer


                                XX. XXXXX X. XXXXX

                                By:     /s/ Xxxxx X. Xxxxx
                                        ---------------------------------------
                                        Name:   Xxxxx X. Xxxxx




                                SFM PARTICIPATION, L.P.

                                By:     SFM AH, Inc.
                                        General Partner

                                By:     /s/ Xxxxxxx X. Xxxxxxx, Xx.
                                        ---------------------------------------
                                        Name:   Xxxxxxx X. Xxxxxxx, Xx.
                                        Title:  Secretary


                                SFM AH, INC.

                                By:     /s/ Xxxxxxx X. Xxxxxxx, Xx.
                                        ---------------------------------------
                                        Name:   Xxxxxxx X. Xxxxxxx, Xx.
                                        Title:  Secretary


                                MR. XXXXXX XXXXX

                                By:     /s/ Xxxxxxx X. Xxxxxxx, Xx.
                                        ---------------------------------------
                                        Name:   Xxxxxxx X. Xxxxxxx, Xx.
                                        Title:  Attorney-in-Fact


                                XXXXX FUND MANAGEMENT LLC

                                By:     /s/ Xxxxxxx X. Xxxxxxx, Xx.
                                        ---------------------------------------
                                        Name:   Xxxxxxx X. Xxxxxxx, Xx.
                                        Title:  Assistant General Counsel