Forty-six patients with acute leukemia were treated with mitoxantrone as a single agent. Twenty-nine patients had relapsed and/or refractory acute leukemia. Seventeen patients with acute non-lymphatic leukemia had received no prior treatment. Twelve mg/m2 of mitoxantrone was given intravenous on five consecutive days. Treatment related side effects included bone marrow suppression, mucositis, alopecia, nausea, vomiting and infection. Cardiotoxicity was documented in 7 patients. This study reconfirms that mitoxantrone is an active agent in acute leukemia with complete response documented in 10 of 29 patients with relapsed and/or refractory acute leukemia (34% response rate, 95% confidence limits 18-53%) and complete response documented in 11 of 17 patients (65% response rate, 95% confidence limits 38-87%) with previously untreated acute nonlymphatic leukemia.