A regimen of aclarubicin (ACR) of 75 mg/m2 daily for 3 days plus a continuous intravenous infusion of cytosine arabinoside (ara-C) of 100 mg/m2 per day for 7 days was compared with daunorubicin (DNR) 45 mg/m2/day for 3 days plus ara-C for 7 days as first-line chemotherapy of de novo acute myeloid leukemia (AML) in a randomized, nationwide Danish study. A total of 180 patients aged between 17 and 65 years were entered onto the protocol. Patients who achieved complete remission (CR) were given five courses of intensive consolidation therapy consisting of two courses of high dose ara-C, two courses of amsacrine plus etoposide, and one course of DNR plus ara-C. Of 174 evaluable patients, 99 achieved CR. The rate of CR was significantly higher on ACR plus ara-C than on DNR plus ara-C [66% versus 50% (p = 0.043)] and decreased significantly with increasing age. The hematological toxicity was identical for the two regimens. A total of 83 patients entered consolidation therapy. At 4 years, 37% of patients with CR following ACR were still in remission compared with 33% following DNR (p = 0.48), and the total survival at 4 years was 29% versus 20% (p = 0.26). The duration of remission and total survival both decreased with increasing age. ACR plus ara-C seem at least as good or better than DNR plus ara-C as first-line chemotherapy of AML.