Yoshi 864 was given i.v. push daily times 5 with 6 weeks' followup. Dose escalation was from 0.25 mg/kg to 2.7 mg/kg. Toxicity and effectiveness were first seen at 1.5 mg/kg. Twenty-five courses were given to 16 patients at or above this level. In 16 of 22 courses, exclusive of CML, thrombopenia and/or leukopenia occurred. Mean platelet and WBC nadirs occurred on day 24 and 29 with recovery taking 1-2 weeks and 2-3 weeks respectively. Hb fell in 11 courses. At 2.7 mg/kg, nausea and vomiting lasting 6-12 days occurred in 3 of 7 courses; during 5 coures patients slept 20 hours a day, and 1 was comatose for 2 days. Two patients with squamous cell carcinoma and 1 with an unknown primary responded. Both patients with CML had clinical remissions. It is recommended that a cooperative Phase II Study in a broad spectrum of human solid tumors including lymphomas and chronic myelocytic leukemia be undertaken at a dose level of 2 mg/kg.