Between September and August 1991 818 previously untreated children and adolescents up to 18 years of age with acute lymphoblastic leukemia were entered into two modified BFM-protocols. Patients with B-ALL were excluded. From 1981 to 1987 524 patients were entered into the randomized multicenter study ALL VII/81 (modified ALL-BFM 81 protocol). Patients were divided into three risk groups standard (SR), medium (MR), high risk (HR) using the BFM risk factor. In a connecting study from 1988 to 1991 294 patients were registered on the stratified and randomized multicentric trial ALL VIII/87 (modified ALL-BFM 86 study). The main modification in study ALL VII/81 concerned the duration of treatment. Patients were randomized into two groups. The first group received as a late reinduction protocol III and then therapy was stopped. The second group received 6-MP and MTX for another six months. The other whole treatment strategy of ALL-BFM 81 was adopted. In protocol ALL VIII/87 the only modification was the reduction of the MTX dosage from 5 g/m2 to 1 g/m2 with an infusion time of 24 hours (leucovorin rescue 15 mg/m2 after 48 and 54 hours). The probability of the event-free-survival (EFS) for study ALL VII/81 was 59%. CNS events were significantly more frequent in standard risk patients with intermediate dose MTX (4 x 0.5 g/m2) compared with the irradiation group (18 Gy). The EFS for SR patients amounts to 61%, for MR patients to 59% and for HR patients to 36%. There was no significant difference of EFS for the two groups with different duration of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)