158 evaluable patients with stage II, lymph node positive, carcinoma of the breast were randomized to adjuvant therapy with either melphalan (L-PAM) or cyclophosphamide, methotrexate, and fluorouracil (CMF) after mastectomy. In addition, patients were randomized to be treated with or without post-operative irradiation therapy (RT) in addition to their chemotherapy. At a median follow-up time of 11 years, there is no difference in time to relapse (P = 0.69) or survival (P = 0.55) among the four treatment groups. Multivariate analysis including treatment arm, age, race, tumor size, histologic type, performance status, time to onset of treatment, menopausal status, and number of positive nodes, revealed that only the number of positive nodes (less than 4 vs greater than or equal to 4) was related to disease-free and overall survival. Ten year relapse-free survival for patients with less than 4 positive nodes compared to those with greater than or equal to 4 positive nodes was 63% versus 30%, and overall survival 63% versus 41%, respectively. Patients who received post-operative radiation therapy had significantly less local recurrence than those treated with chemotherapy alone (P = 0.03) but without improvement in relapse-free or overall survival. In this trial, post-operative radiation therapy when added to chemotherapy decreased the risk of local recurrence without adverse effects on survival. Treatment outcome was not influenced by chemotherapy regimen, but differences may have been obscured by the small sample size.