We report the toxicity and efficacy of a new conditioning regimen for bone marrow transplantation (BMT) in children with poor prognosis neuroblastoma (NBL). Twenty-seven patients with poor prognosis NBL were treated with teniposide (360 mg/m2) or etoposide (500 mg/m2), thiotepa (600-900 mg/m2), and 1200 cGy fractionated total body irradiation (fTBI) followed by autologous marrow rescue (n = 19) or allogeneic BMT from HLA-identical siblings (n = 8). The two patients who received teniposide, 600 mg/m2 thiotepa and fTBI had minimal toxicity but relapsed 4 and 12 months post-auto BMT. The next two patients received 750 mg/m2 thiotepa, 500 mg/m2 etoposide and TBI. They tolerated the conditioning regimen well and are alive and in remission 77 and 75 months post-BMT. At the next thiotepa dose level (900 mg/m2), the first two allograft recipients both experienced fatal regimen-related toxicity. All subsequent allograft recipients received 750 mg/m2 thiotepa and autograft recipients received 900 mg/m2 thiotepa. As of 1 April 1995, eight of the 19 patients who received autologous marrow are surviving disease-free 21 to 77 months post-BMT. Nine autograft recipients relapsed at 2 to 37 months following transplantation. One patient died of hepatic veno-occlusive disease 2 months after auto BMT, and one of pneumonia 6 months post-transplantation. Three allograft recipients have relapsed at 6, 10 and 39 months post-transplant and three are alive and in remission 75, 53 and 27 months post-BMT. Overall, 11/27 patients (41%) are alive and in remission 21-77 months (median 47 months) following BMT. A conditioning regimen consisting of 500 mg/m2 etoposide, thiotepa (750 mg/m2 for allograft recipients and 900 mg/m2 for autograft recipients) and 1200 cGy fTBI has acceptable toxicity and is at least as effective as melphalan-containing regimens in the treatment of high-risk NBL.