Prolonged cyclic combination chemotherapy with cyclophosphamide, methotrexate and fluorouracil was evaluated as adjuvant treatment to radical mastectomy in primary breast cancer with positive axillary lymph nodes. After 27 months of study, treatment occurred in 24 per cent of 179 control patients and in 5.3 per cent of 207 women given combination chemotherapy (P less than 10(-6)), the advantage appearing statistically significant in all subgroups of patients. Patients with four or more positive axillary nodes had a higher per cent of relapses than those with fewer nodes. The initial new clinical manifestations occurred in distant sites in 81.5 per cent of relapsed patients. Long-term chemotherapy produced an acceptable toxicity, thus allowing the administration of a high percentage of drug dosage. These results should be considered with caution, since, at present, the effect of this therapy on survival and possible long-term side effects remain unknown.