The efficacy of the addition of intensive therapy with daunorubicin (45 mg/m2 IV on days 1, 2, 3) to an otherwise identical induction program consisting of vincristine, prednisone, and L-asparaginase was assessed in 177 previously untreated adults (greater than or equal to 20 years of age) with acute lymphocytic leukemia (ALL). In the prospectively randomized phase of the investigation, 46 patients received daunorubicin in induction, whereas 53 did not. The two groups were otherwise comparable for pretreatment variables. A complete response was observed in 38/46 patients (83%) treated with daunorubicin, compared to 25/53 (47%) induced with vincristine, prednisone, and L- asparaginase alone (P = .003). The high response rate attributable to the use of the anthracycline was confirmed by the nonrandomized treatment of 78 subsequent patients, in whom a complete response rate of 76% was attained. A common program for central nervous system therapy and for maintenance therapy was employed in 103 patients achieving complete response. Maintenance consisted of cycles of 6- mercaptopurine (6-MP) and methotrexate with periodic reinforcement with vincristine and prednisone. Maintenance therapy proved to be minimally toxic. The average duration of complete response was 15 months and was not affected by the induction program employed. Approximately 25% of responders are projected to remain in continuing complete response for 36 months. The failure of the daunorubicin-containing programs to produce a higher percentage of long-term survivors, despite the higher complete response rates achieved, was thought to be due to the use of a maintenance program that was weak in intensity and dependent on reinforcement with vincristine and prednisone. These data clearly establish the increased effectiveness of vincristine, prednisone, L- asparaginase, and daunorubicin, as compared to this combination without daunorubicin, in the induction of complete response in adults with ALL. The results support the concept of an intensive, rather than a conservative, chemotherapeutic approach as the most appropriate strategy for the treatment of adult ALL.