Two hundred and seventeen patients, 1-50 yr old, with acute lymphoblastic leukemia in complete remission were randomized to receive a 1-yr consolidation chemotherapy of either type P, comprising 7 different drugs, or type M, consisting of methotrexate interspersed with prednisone and vincristine. Thereafter, they were randomized a second time to receive a 4-yr maintenance of either chemotherapy or immunotherapy, comprised of allogeneic blasts and bacillus Calmette-Guérin (BCG). Consolidation P caused more toxicity than consolidation M. However, comparison between the consolidation therapies P and M showed no significant difference, neither for disease-free interval nor for duration of survival. Chemotherapy showed more lethal toxicity in adults than in children. Comparison between chemotherapy (C) and immunotherapy (I) as maintenance treatment showed a significant (p = 0.016) superiority of C for disease-free interval (DFI). The difference was even more pronounced (p = 0.009) in the group with less than 8 g/dl of hemoglobin (Hb) at diagnosis before therapy. On the other hand, for patients with more than 8 g/dl Hb at diagnosis, presumably those with T-ALL, no difference in DFI was seen. No difference has been seen so far between maintenance therapies I and C concerning the duration of survival. The patients who were receiving maintenance I when they relapsed and who were consequently retreated by chemotherapy, survived longer from relapse than those patients retreated for relapse while receiving maintenance C.