Seventy-six patients between the ages of 2 and 17 years with acute lymphoblastic leukemia (ALL) achieved a second complete remission induced by polychemotherapy. Twenty-one had an HLA-identical donor and underwent allogeneic bone marrow transplantation (BMT) after conditioning with total body irradiation and cyclophosphamide. The remaining 55 patients lacked a suitable donor and received intensive chemotherapy as treatment. Fifteen patients were excluded from the analysis because they relapsed within 3 months after achieving a second complete remission. Three of the 21 BMT patients died of transplant-related complications and seven relapsed between 90 and 480 days after transplantation. Eleven patients are alive and disease free at 5.5-71 months with an actuarial survival of 47.1%; eight patients are on a plateau extending from 22 to 71 months. Thirty-three patients treated with chemotherapy died from relapse and seven are alive and disease free 7.5-99 months from the second remission, with an actuarial survival of 9%. The probability of survival was significantly higher in the BMT group (p less than 0.025). The probability of remaining in complete remission in the BMT group was 58.5% versus 10.9% in the chemotherapy group (p less than 0.005). Our results show that BMT is the best alternative therapy for children affected by ALL who have had a relapse in the marrow.