A clinical study started at the Institute in 1975 embraced 1,228 patients with breast tumors of stages I, II and III. Adjuvant monochemotherapy (six courses of 200 mg Thio-TEPA) was followed by a 24.3% decrease in the death rates for the patients with stage I-II tumors (pT0-2N0-1M0), whereas polychemotherapy (six courses of TMF and CMF)-by 32.4%. A 7.8-9.8% increase in corrected survival (as compared with control) was registered in those patients with less advanced malignancies of the breast (pT0-2N0M0) who had received mono- and polychemotherapy. In patients with pT0-2N0-1M0 tumors treated after the TMF or CMF modalities, survival rates showed a 12.0-16.6% increase, as compared with controls, after 6, 7 and 8 years. The beneficial effect of adjuvant chemotherapy (lower mortality rate matched by higher survival) was reliably established in patients under 50 only.