Homoharringtonine is one of a group of cephalotaxine esters reported by the Chinese to have significant antitumor efficacy, with particularly good activity in human leukemias. Preclinical antitumor activity against P388 leukemia, colon 38 carcinoma, and mammary carcinoma led to phase I trials which are currently nearing completion in this country. The phase I study reported here used a single infusion of homoharringtonine over 90 minutes given every 21 days. Dose-related and life-threatening hypotension, without significant myelosuppression, was the dose-limiting toxic effect. The mechanism of hypotension is not understood but it is not related to cardiac arrhythmias. Myelosuppression was not seen regularly. We do not recommend this schedule for phase II trials.