In an attempt to improve the poor prognosis of poor responders with stage IV neuroblastoma, a new combined high-dose chemotherapy conditioning regimen was tested. Event-free and overall survival, as well as the incidence of complications, were analysed. Twenty-five children aged 12-146 months at diagnosis entered this study. All were in complete remission (CR) at the time of high-dose chemotherapy. Two or three different protocols had been necessary for them to achieve a CR. High-dose chemotherapy consisted of a combination of busulfan (600 mg/m2), cyclophosphamide (4400 mg/m2) and melphalan (140 mg/m2). It was followed by autologous bone marrow transplantation (ABMT). The bone marrow graft was purged in vitro with mafosfamide. The probability of event-free survival (EFS) at 5 years post-ABMT was 34%, compared to < 8% in a historical series. Toxicity was severe but manageable and 2 complication-related deaths were observed. Veno-occlusive disease was the most frequent extrahaematopoietic complication encountered, but its outcome was always favourable. By using a very intensive conditioning regimen consisting of a combination of three alkylating agents, the EFS of poor responders with metastatic neuroblastoma was improved and similar to that of good responders. When compared with a previously published similar series of patients, the improvement in survival appears probably related to intensification of the conditioning regimen.