Seventeen patients with relapsed or refractory acute nonlymphocytic leukemia were treated with 14 mg/m2 of mitoxantrone given in a 30-minute infusion daily for three days. If the day fourteen bone marrow showed residual leukemia, a second course was given at the same dose for two days. Eight patients (47%) entered complete remission. Three patients (17%) had a partial response, four (24%) did not respond, and two (12%) died with hypoplastic marrows during treatment. Seven of the 12 relapsed patients entered a complete remission, as did one of the five refractory patients. Toxicity was acceptable; prolonged myelosuppression, moderate hepatic toxicity, and stomatitis were the only problems. Several dose schedules of mitoxantrone have been studied by other investigators with varying results. The three-day schedule in the present study is similar to the schedule used for common induction regimens employing anthracycline drugs. On the basis of its activity and acceptable toxicity in relapsed and refractory ANLL patients, we feel that this schedule could be safely combined with other agents in future studies.