This prospective randomized clinical trial was to clarify whether postremission therapy without prednisolone (PSL) was more effective than therapy with PSL in improving the 5-year survival of adults with acute leukemia. Thirty consecutive adult patients with newly achieved complete remission were randomized to receive postremission therapy either with or without PSL between September 1985 and September 1988. The patients ranged from 16 to 57 years in age. Patients treated without PSL had a significantly better 5-year survival rate than those receiving PSL according to Kaplan-Meier analysis (53.5% vs 15.3%, p < 0.05). In the group treated without PSL, eight out of 15 patients were alive at 72 months, and seven patients maintained their first complete remission at 72 months. Among patients with acute lymphoblastic leukemia (ALL) who were treated without PSL the median duration of remission was 24 months, and the survival rate at 72 months was 50.0%. On the other hand, the median survival was only 13 months for the 5 patients with ALL treated with PSL. Thus, it is desirable that adults with acute leukemia are treated by postremission therapy without PSL.