Aclarubicin, a new anthracycline antibiotic, was used to treat 24 adult patients with refractory adult leukemia, using a total dose of 300 mg/m2 (75 mg/m2/day X 4). There were 20 patients with acute myelogenous and four with acute lymphoblastic leukemia. Approximately two-thirds of the patients had a Karnofsky score of less than or equal to 2, and two-thirds had received two or more previous induction programs. Interim bone marrow evaluation was obtained in 18 of 30 remission induction courses and revealed marked hypocellularity in 14, inadequate specimens in three, and persistent disease in one. Seven patients received more than one course. Two patients refused further therapy. In patients with myelogenous leukemia, there were two complete remissions lasting 10 and 16 months and one partial remission lasting 4 1/2 months. There were no responders in patients with lymphoblastic leukemia. Toxicity included profound leukopenia and thrombocytopenia, moderate nausea and vomiting, diarrhea, and mucositis. There were no cardiac symptoms associated with the drug infusion, but there were three late events possibly associated with anthracycline cardiotoxicity. Used in this dosage schedule, aclarubicin is an active, but toxic, agent in the acute myelogenous leukemias.