Twenty-four patients with acute leukemia and blast crisis of chronic myelocytic leukemia in relapse or refractory to standard chemotherapy were eligible for treatment with mitoxantrone. Mitoxantrone was administered in a dose of 8-13 mg/m2 on five consecutive days. 5 of 20 evaluable patients were induced into complete remission, 1 patient achieved a partial remission. Side effects included moderate to severe bone marrow suppression, moderate mucositis and hair loss. No cardiotoxicity was observed. We believe that mitoxantrone is an active agent in the treatment of acute leukemia and suggest further studies in combination chemotherapy.