Analysis of recurrence rates in male breast cancer (MBC) has suggested that tumor size and degree of axillary lymph node involvement carry the same prognostic implications as for breast cancer in women. A similar spectrum of antineoplastic agents appears active in both females and males. Based on reports of active adjuvant chemotherapy of women with breast cancer, we initiated a trial of adjuvant chemotherapy of MBC in July 1974. Twenty-four patients have been treated with cyclophosphamide, methotrexate, and 5-fluorouracil (CMF). All patients had nodal involvement (median three nodes positive; seven patients had a single positive lymph node). All patients began adjuvant therapy within 4 weeks of either a radical or modified radical mastectomy. No postoperative radiotherapy was given. Median potential follow-up is 46 months. Four patients have recurred, one each at 15, 45, 61, and 65 months following mastectomy; two are dead of metastatic disease. The five-year survival rate projected by actuarial means is in excess of 80% (95% confidence interval: 74-100%). Based on these data, this treatment is highly encouraging when compared to other forms of treatment reported in the literature in which 5-year disease-free survival rates are less than 30%. We conclude that adjuvant therapy of MBC with a CMF regimen is feasible and may be associated with substantial improvement in disease-free survival and overall survival.