Cephalotaxine alkaloids have been extensively used in the Peoples Republic of China for treatment of acute leukemias and solid tumors (Yu-hua, L., Shu-fen, G., Fu-ying, Z., Shu-zhi, X., and Hui-lin, Z. Chin. Med. J., 96: 303-305, 1983). Several Phase I trials of homoharringtonine have been completed in the United States using either bolus administration or continuous infusion over a 5-day period. The major toxicities have been hypotension following rapid administration and myelosuppression when lower doses are infused over 5 to 7 days. None of these studies, however, reproduce the schedule used in China which is i.v. infusion of approximately 1 mg/day over 4-8 h for a period of 14-28 days or more, followed by a rest period of approximately 7-14 days. This study more closely reproduces that schedule as a Phase I trial by decreasing the daily dose of homoharringtonine and using a continuous infusion schedule to allow escalation of total days of treatment. Forty-eight patients entered the study. The final recommended dose of homoharringtonine is 1 mg/m2/day for 30 days followed by a 2-week rest period. The dose limiting toxicity of myelosuppression was severe and prolonged in some patients. Nonhematological toxicities were minimal and generally well tolerated. Patients should be followed with at least weekly blood counts and treatment interrupted pending full marrow recovery if the granulocyte count falls below 1,000/mm3 or the platelet count falls below 100,000/mm3.