Fifty-eight evaluable patients with acute leukemia were treated with Mitoxantrone (DHAD) according to two schedules: 14 mg/M2 as a single I.V. pulse dose administered three-week intervals, and 4 mg/M2/day for five days every three weeks. Six of 58 patients achieved a complete remission. One complete remission and 1 partial remission were observed among 26 patients treated with the single pulse schedule. Five (16%) complete remissions were attained among 32 patients treated on the daily x 5 schedule. Responses were observed only in patients with non-lymphoblastic leukemia. DHAD was very well tolerated with myelosuppression as the major toxicity. Nausea and vomiting were minimal. Subclinical cardiac toxicity occurred in two patients. This was identified by serial reductions in cardiac ejection fractions. DHAD appears to have significant activity in acute non-lymphoblastic leukemia with minimal toxicity.