Fifty-seven adult patients with acute promyelocytic leukemia (APL) were treated between 1974 and 1984 with daunorubicin (DNR) or 4-(9- acridinylamino)methanesulfan-m-anisidide (AMSA) in combination with arabinosylcytosine (Ara-C) and 6-thioguanine (TG); they also received prophylactic heparin. Forty-one patients (72%) achieved complete remission (CR), including 11 of 12 patients who received the AMSA- containing regimen. The incidence of early fatal hemorrhage was 14%, lower than that of earlier studies or other published reports. Elevated WBC and serum lactate dehydrogenase levels at diagnosis were associated with an increased incidence of life-threatening hemorrhage and shorter remission duration. Advanced age was an unfavorable prognostic factor for male patients. Both DNR and AMSA in combination protocols are effective treatments for APL. The incidence of CR is similar to that achieved in other types of acute nonlymphoblastic leukemia (ANLL) with the same protocols, but the median duration of remission is significantly longer in APL (24 v 9 months) and the percentage of remissions longer than 60 months is also higher in APL (35% v 5%).