We conducted a phase II study on 19 children with AML in first (10 patients) or second (nine patients) complete remission (CR) treated with ABMT, evaluating the combination of total body irradiation (TBI, 12 Gy in six divided fractions) and high-dose melphalan (140 mg/m2 in single dose) in an attempt to improve antitumour efficacy of conditioning regimen. All patients received cryopreserved and in vitro purged (mafosfamide at a dose of 100 micrograms/ml) bone marrow. The median time from first CR to ABMT was 5 months compared with a median time of 3 months for patients in second remission. One of the 19 patients, transplanted in second CR, died of transplant-related complication 10 days after transplant and another second CR patient relapsed on day +28, before engraftment. Three further patients in second CR relapsed at 6, 6 and 18 months after marrow transplant, respectively, and this determined a relapse rate of 43% in children given ABMT in second CR and 0% for patients transplanted in first remission (P < 0.05). Seventy-two per cent of all patients are projected to be alive and disease-free at 6 years, whereas the event-free survival of patients in first and in second CR is 100 and 44%, respectively (P < 0.05). Although the number of patients does not allow us to draw any firm conclusion, our results are encouraging and suggest that the association of TBI and high-dose melphalan appears to be safe and valuable.