
<PAGE>

                                                                    Exhibit 99.1
                                                                    ------------

                                   AGREEMENT

          Pursuant to Rule 13d-1(k)(1) promulgated pursuant to the Securities
Exchange Act of 1934, as amended, the undersigned agree that the attached
Schedule 13G is being filed on behalf of each of the undersigned.

February 14, 2000        VENROCK ASSOCIATES

                         By:  /s/ Ted H. McCourtney
                              -----------------------
                                  Ted H. McCourtney
                                  General Partner


February 14, 2000   VENROCK ASSOCIATES II, L.P.


                         By:  /s/ Ted H. McCourtney
                              -----------------------
                                  Ted H. McCourtney
                                  General Partner


February 14, 2000   GENERAL PARTNERS


                                      *
                         ------------------------------
                         Anthony B. Evnin

                                      *
                         -----------------------------
                         David R. Hathaway

                                      *
                         -------------------------------
                         Patrick F. Latterell

                                      *
                         ------------------------------
                         Ted H. McCourtney

                                      *
                         -------------------------------
                         Ray A. Rothrock

                                      *
                         -------------------------------
                         Kimberley A. Rummelsburg

                                      *
                         -------------------------------
                         Anthony Sun



          * By:  /s/ Ted H. McCourtney
                 ----------------------
                     Ted H. McCourtney
                     Attorney-in-Fact


                              Page 17 of 17 pages
