OUTLINE: This is a dose escalation, multicenter study. Patients receive SU5416 by intravenous injection twice weekly for 4 weeks. Patients may continue treatment for a maximum of 1 year in the absence of disease progression and unacceptable toxicity. In the absence of dose limiting toxicity (DLT) in the first 6 patients treated, subsequent cohorts of 6 patients each receive escalating doses of SU5416 on the same schedule. If DLT occurs in 2 of 6 patients at a given dose level, then dose escalation ceases and the next lower dose is declared the maximum tolerated dose (MTD). Six additional patients are treated at the MTD. Patients are followed at 30 days after the last treatment, and every 3 months thereafter.