A randomized comparison of the relative efficacy and toxicity of daunorubicin (DNR) at 30 or 45 mg/sq m or adriamycin (ADM) at 30 mg/sq m, given on the first 3 days of a 7-day continuous infusion of cytosine arabinoside (ara-C) at 100 mg/sq m/day, shows the outcome to be dependent on anthracycline, dose, and patient age. DNR 45 is significantly better than DNR 30 or ADM 30 for inducing complete remissions (CR) in patients younger than 60 yr, (72%, 59%, 58% CRs, respectively). DNR 30 is better than DNR 45 or ADM 30 for inducing CR in patients older than 60 yr (47%, 31%, 35%, respectively). There was a corresponding shift in the induction mortality for the age, dose, and anthracycline groups. Adriamycin was significantly more toxic to the gastrointestinal tract than daunorubicin. The duration of complete remission, with cyclic courses of maintenance therapy, was independent of the patient's age, the dose, or choice of anthracycline used in induction, and of whether the maintenance courses were given every 4 wk or every 8 wk.