327 patients with cancer of the breast and involvement of axillary lymph nodes were randomised, after total mastectomy and axillary clearance, to receive either no additional treatment or oral cyclophosphamide 80 mg/m2 on days 1-14, intravenous methotrexate 32 mg/m2 on days 1 and 8, and intravenous fluorouracil 480 mg/m2 on days 1 and 8 (CMF), which was repeated every 28 days for twelve cycles. There was a significantly longer relapse-free survival (RFS) in patients treated with CMF. A prolonged RFS was seen in premenopausal patients, those with 1-3 nodes involved, and those with 4 or more nodes involved, but a similar trend in postmenopausal patients failed to reach statistical significance. RFS was greater in patients with CMF-induced amenorrhoea than in controls and in treated patients whose primary tumour contained progesterone receptors. Dose of chemotherapy did not have a significant effect on RFS. Survival was not influenced by treatment.