Patients with acute nonlymphocytic leukemia were given remission induction therapy consisting of cytosine arabinoside and an anthracycline. Those patients who experienced complete remission received two courses of consolidation therapy and were randomized to receive maintenance therapy consisting of either daily chemotherapy with reinforcements every 3 mo or reinforcement therapy only every 6 wk. The overall complete remission rate was 66%, with 80% complete remission for previously untreated patients less than 60 yr of age who did not have a prior history of malignancy. Remission durations were the same for patients treated with both maintenance regimens. The major determinant for successful remission induction therapy was patient age, with older patients frequently succumbing to intercurrent infection. Documented leukemic cell resistance to the therapy employed was only rarely encountered. Once remission was achieved, age was no longer a determinant of patient survival, since duration of remission was independent of age. Remission durations were directly related to leukemic cell retention of cytosine arabinoside triphosphate. Hence therapy for acute nonlymphocytic leukemia can be divided into two separate areas: remission induction and remission maintenance.