Five-year results of a prospective, randomized clinical trial of three treatment regimes--(a) cytoxan, methotrexate, and 5-fluorouracil (CMF); (b) CMF plus the antiestrogen drug, tamoxifen (CMFT); and (c) CMFT plus bacillus Calmette-Guerin (BCG) vaccinations--in 312 women with stage-II breast cancer are reported. Estrogen receptors (ER) were measured in all of the primary tumors. Addition of tamoxifen to CMF therapy significantly decreased the number of recurrences at five years in ER positive patients with four or more positive axillary lymph nodes. Addition of tamoxifen to CMF had no effect on disease-free survival in ER-positive patients with 1-3 positive axillary lymph nodes or in patients with ER-negative tumors. Addition of BCG vaccinations had no discernible effect on disease-free survival. ER measurements in the primary tumor provide important prognostic information regardless of treatment, with ER-positive patients having lower recurrence rates and mortality after five years. ER measurements also have predictive value for response to endocrine therapy. Further follow-up is needed to determine whether tamoxifen is delaying recurrence or preventing it in a subset of these patients.