OUTLINE: This is a randomized, multicenter study. Patients are randomized twice during the study: prednisolone vs dexamethasone and mercaptopurine vs thioguanine. Patients are initially stratified according to risk status (standard vs intermediate vs high). Patients are stratified at the second randomization according to gender, age (under 2 years vs 2 to 9 years vs over 9 years), WBC (under 50,000/mm^3 vs over 50,000/mm^3), steroid allocation, and early response (slow vs rapid).