Three to 4 weeks after hematological recovery from this consolidation CT, patients who were still in CR were randomized both to receive or not receive intermittent ATRA (45 mg/m2/d, 15 days every 3 months) and to receive or not receive continuous CT with 6 mercaptopurine (90 mg/m2/d, orally) and methotrexate (15 mg/m2/wk, oral-ly), according to a 2-by-2 factorial design stratified on the initial induction treatment group. Maintenance treatment was scheduled for 2 years. Randomizations for induc-tion and maintenance, stratified on center, were performed through a centralized tele-phone assignment procedure.