There is strong evidence that corticosteroids contribute to the objective and subjective response rate observed following treatment with several cytotoxic chemotherapy agents, and that there is a dose response effect for treatment of multiple myeloma with alkylating agents. Therefore, the Eastern Cooperative Oncology Group (ECOG) studied cyclophosphamide 600 mg/M2 given for four consecutive days intravenously combined with prednisone 100 mg orally daily in 57 patients who had progressed following or failed to respond to standard doses of these drugs. Forty eight patients met the eligibility criteria for evaluation of response and toxicity. Fourteen patients (29%) had an objective response (OR) and an additional 2 (4%) had a subjective response (SR) only. The median duration of objective response was 3.1 months and estimated median survival was 8.6 months. These results are identical to our prior experience with high dose cyclophosphamide alone. The addition of prednisone does not appear to enhance results either through increased remissions or greater survival. Therefore, this study indicates that the preferred form of high dose cyclophosphamide for multiple myeloma is as a single agent given in intravenous four day courses.