A randomized trial was carried out in 55 institutes in the Tohoku district to examine the significance of breast cancer post-operative adjuvant chemo-endocrine therapy in stage II and IIIa patients for possible radical mastectomy. A total of 619 patients were entered from November 1982 to November 1984, of whom 554 were eligible. Patients were administered MMC 13 mg/m2 after surgery, and randomized using the envelope method into either group A, treated with Tegafur 400 mg/m2 alone (275 patients), or group B, treated with Tegafur 400 mg/m2 and Tamoxifen 20 mg/daily (279 patients), for a year from the 7th day after operation. There was no significant difference between the two groups in the background factors of age, menopausal status, operation methods, stage or number of positive lymph nodes, but there were more patients of ER(+) in group B. A Kaplan-Meier method comparison showed no significant difference between the two groups in 3-year disease-free survival rates. There was no significant difference between the two groups compared by ER or menopausal status. However, patients with 4 or more positive lymph nodes showed a significant benefit in group B. Group B also marked a higher disease-free survival rate for ER(+) patients with 4 or more positive lymph nodes.