Twenty-six adults, ages 27 to 60, with refractory metastatic solid tumors were treated with high-dose cyclophosphamide (Cy) + carmustine (BCNU) at one of three escalating dose schedules followed by autologous bone marrow transplantation (ABMT). Toxicity was severe and dose-related, with the maximum tolerated dose for the combination determined to be Cy 160 mg/kg and BCNU 900 mg/m2. Median time to WBC recovery (greater than or equal to 1,000/microL) was 13 days post-ABMT (range, nine to 22 days) and to a platelet count of greater than or equal to 50,000/microL, 22 days (range, 13 to 83 days). Sixteen of 20 evaluable patients (80%) responded to therapy with at least 50% reduction in measurable tumor, and three patients achieved complete remission (CR). Responders included eight of nine evaluable patients with breast carcinoma, two of five with melanoma, two of two with sarcoma, and four of four with colon carcinoma. Response durations were short (median, 4 months), even for complete responders, and relapses generally occurred at sites of previous metastases. In order for this approach to have a more significant impact on overall survival, it may need to be applied earlier in the natural history of the malignancy.