Cohorts of 3-6 patients receive escalating doses of SU5416 until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that at which 2 of 3 or 2 of 6 patients experience dose-limiting toxicity. Once the MTD has been determined, additional patients are accrued to the phase II portion of the study. These patients receive SU5416 IV, as in the phase I portion, at the appropriate MTD established in phase I.