SummaryTwenty-five patients with advanced metastatic breast cancer were treated with the combination of methotrexate 60 mg/M2 and 5-fluorouracil 700 mg/M2 intravenously on the first and eighth days, and cyclophosphamide 100 mg/M2 and prednisone 40 mg/M2 by mouth daily for the first 14 days of a 28-day cycle. The patients had had no previous chemotherapy or extensive radiotherapy and all but two had not responded to hormonal therapy or endocrine ablation. The major metastatic lesions were: lung (12 patients), liver (four patients), bone (four patients), soft tissue (three patients), nodes (two patients). Seventeen of the 25 patients (68oo) responded to treatment with seven complete remissions; these included patients suffering metastatic lesions in the lung, nodes, and soft tissue. The overall median duration of response was nine months (range 6-26 months). Toxicity was primarily haematological, but the group received an average of at least 75% of their calculated dose for each monthly cycle. Haematological toxicity was most pronounced in patients with liver dysfunction and bone marrow involvement. Out of eight nonresponders seven died, with a median survival of six months. Only six of 17 responders died, and the median survival in this group will exceed thirteen months. There was no correlation between the length of the metastasis-free interval after previous treatment and subsequent response to chemotherapy.