Neuroblastoma and Ewing's sarcoma are examples of pediatric cancers in which disseminated disease is often present at diagnosis or develops later in spite of combination therapy. The demonstration that marrow-ablative doses of chemotherapy can increase tumor cell kill, and that autologous bone marrow can be cryopreserved and reinfused into the patient to reverse such marrow ablation, has stimulated interest in this approach to refractory childhood cancers. We present results of treating eighteen patients with recurrent neuroblastoma and Ewing's sarcoma resistant to conventional therapy. We used supralethal doses of melphalan, supported by reinfusion of previously cryopreserved autologous bone marrow. Seven of 10 neuroblastoma and six of eight Ewing's sarcoma patients had complete or partial responses, lasting for a median of 6 months (neuroblastoma) and 3 months (Ewing's sarcoma). Prolonged hospitalization, pancytopenia complicated by sepsis, and reversible gastrointestinal toxicity were the major side effects. These results suggest this approach should be tested in therapeutic trials at an earlier disease stage in children who have cancers with a predictably bad prognosis.