Twenty-four patients with acute leukemia or blast crisis (BC) of chronic myelocytic leukemia (CML) in relapse or refractory to standard chemotherapy, were eligible for treatment with mitoxantrone. Mitoxantrone (Novantrone; dihydroxyanthracenedione) was administered in a dose of 8-13 mg/m2 on five consecutive days. Five of 20 evaluable patients were induced into complete remission, one 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.