s/Anthony B. Evnin --------------------------- Anthony B. Evnin /s/David R. Hathaway --------------------------- David R. Hathaway /s/Patrick F. Latterell --------------------------- Patrick F. Latterell /s/Ted H. McCourtney...

                                                                    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/▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇
                              --------------------
                                ▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇
                                General Partner

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


                         By:  /s/▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇
                              --------------------
                                ▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇
                                General Partner


February 14, 2000    GENERAL PARTNERS


                         /s/▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇
                         ---------------------------
                         ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇

                         /s/▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇
                         ---------------------------
                         ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇

                         /s/▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                         ---------------------------
                         ▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇

                         /s/▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇
                         ---------------------------
                         ▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇

                         /s/▇▇▇ ▇. ▇▇▇▇▇▇▇▇
                         ---------------------------
                         ▇▇▇ ▇. ▇▇▇▇▇▇▇▇

                         /s/▇▇▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇▇
                         ---------------------------
                         ▇▇▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇▇▇

                         /s/▇▇▇▇▇▇▇ Sun
                         ----------------------------
                         ▇▇▇▇▇▇▇ Sun

                              Page 16 of 16 pages