During a phase I clinical and pharmacologic trial, 26 patients with refractory solid tumors were treated with increasing doses of adozelesin by brief intravenous Infusion every 3 weeks. Overall, adozelesin was well tolerated. The dose-limlting toxicity was myelosuppression, mainly thrombocytopenia and leukopenia. Nonhematologic toxicity was generally mild, with fatigue (36%), local reaction at the infusion slte (24%), nausea or vomlting (20%) and hypersensitivity reaction (16%) being the most common adverse effects. There were no objective clinical responses. The maximally tolerated dose on this schedule was 188 μg/m2with the recommended phase II starting dose being 150 μg/m2on an every 3 week schedule. Adozelesin merits broad investigation at the phase II level.