The aim of study LAL 17/84 was to reduce the number of relapses by intensifying initial treatment. Patients were classified as high (HR) and standard-risk (SR) groups following the established risk index. Early response, after 2 weeks of treatment was also considered. SR protocol includes a ten-week induction and CNS prophylaxis phase: in the first 5 weeks, prednisolone (PRED), vincristine (VCR), daunorubicin (DAUNO) and asparaginase (ASPAR) are given; in the last 5 weeks two intravenous infusions of Ara-C and three of intermediate dose (ID) methotrexate (MTX) are administered simultaneously with 5 it injections of both drugs. CNS prophylaxis is completed with 5 further it injections: one at the beginning and 4 at monthly intervals from the 3rd to the 6th months. In the HR protocol, the initial phase lasts 16 weeks: in the first 5 the same drugs as in SR are used but doses of PRED and ASPAR are higher. CNS prophylaxis includes holocranial radiotherapy (18 Gy), 2 iv infusions of Ara-C and a further 2 of MTX ID and 6 it doses of MTX and Ara-C. Finally, a consolidation phase of PRED, VCR (3 doses), tenoposide (3 doses) and cyclophosphamide is given. Complementary chemotherapy in both protocols consists of daily mercaptopurine and weekly MTX for 2 years; moreover, the randomized half of the patients received monthly reinforcements with PRED, VCR (and DAUNO in HR group) for 4 months. Between Oct. 83 and Nov. 87,87 patients with ages between 3 months and 15 years were enrolled; 86 are evaluable. All achieved remission.(ABSTRACT TRUNCATED AT 250 WORDS)