18 patients with progressive metastatic carcinoma of the breast were treated with 5-FU, MTX, VCR, CYT, and prednisone. A complete response was obtained in six patients, a partial response in four patients, and an additional four patients showed no progression for 5, 6, 7.5, and 10 months. The remaining four patients experienced progressive disease; however, two of these did not receive adequate doses. Chemotherapy had to be temporarily discontinued because of white blood cell counts below 2,000 and/or platelet counts below 75,000 in four patients. One patient had significant nausea and anorexia so that she refused further therapy. Six patients developed a nonbacterial pneumonitis. Other toxicity was mild and did not interfere with daily activities. This is a moderately well-tolerated regimen, and the results compare favorably with those of single agents.