From 1987 to 1995, 22 children with refractory solid tumors entered a phase II study of high-dose thiotepa (HDT) (900 mg/m2) followed by stem cell transplantation (SCT) in the Pediatrics Department of the Institut Gustave Roussy. Tumor types were rhabdomyosarcoma (eight), osteosarcoma (seven), neuroblastoma (three), Ewing's sarcoma (three) and Burkitt's lymphoma (one). Before HDT, all had been extensively treated with conventional chemotherapy, surgical resection of the primary tumor (13/22) and of metastases (6/22), and radiotherapy of the primary tumor in three patients. All had measurable disease, at the site of the primary tumor (3 patients), of the metastases (9 patients) or both (10 patients). Toxicity from the HDT was severe but acceptable. No toxicity-related death occurred. The median duration of neutropenia and thrombocytopenia was 18 days (5-37) and 30 days (7-377), respectively. Septicemia was documented in four patients. Severe diarrhea was observed in seven patients. Mild hepatic toxicity occurred 18 times. No CR and 11/22 PR were documented: osteosarcoma 4/7, rhabdomyosarcoma 4/8, Ewing's sarcoma 2/3; 1/1 Burkitt's lymphoma progressed. We conclude that at a dose of 900 mg/m2 followed by SCT support in these heavily pretreated children, the main toxicity induced by thiotepa was digestive. The response rate observed, especially in sarcoma, is particularly encouraging. Thiotepa should be further evaluated in HDC regimens either in combination with other alkylating agents or in rapidly cycled courses of HDC with SCT.