EXHIBIT 99.1

   1

                                  EXHIBIT 99.1

                             JOINT FILING AGREEMENT


               We, the signatories of the statement to which this Joint Filing
        Agreement is attached, hereby agree that such statement is filed, and
        any amendments thereto filed by either or both of us will be filed, on
        behalf of each of us.

        Dated:  February 11, 2000.

                                            VULCAN VENTURES INCORPORATED



                                            By: /s/ Xxxxxxx X. Xxxxx
                                               ---------------------------------
                                               Xxxxxxx X. Xxxxx, Vice President


                                                              *
                                            ------------------------------------
                                            Xxxx X. Xxxxx


                                           *By: /s/ Xxxxxxx X. Xxxxx
                                               ---------------------------------
                                            Xxxxxxx X. Xxxxx as Attorney-in
                                            Fact for Xxxx X. Xxxxx pursuant to
                                            a Power of Attorney filed on August
                                            30, 1999, with the Schedule 13G of
                                            Vulcan Ventures Incorporated and
                                            Xxxx X. Xxxxx for Pathogenesis,
                                            Inc. and incorporated herein by
                                            reference.