Groups of 3-6 patients are sequentially assigned to receive escalating doses of SU5416 in 33% increments. Study drug is administered as a twice-weekly intravenous injection for 4 weeks. In the absence of unacceptable toxicity, responding patients may continue on SU5416 in 4-week treatment cycles for a maximum of 1 year or until the presence of unacceptable toxicity or tumor progression.