This study tried to evaluate the impact of adjuvant chemotherapy on the induction of chemoresistance in radically operated upon breast cancer patients. Remission rate, remission duration and survival of a group of women (n = 22) treated with combination chemotherapy (adriamycin and cyclophosphamide, AC) for recurrent breast cancer after failed adjuvant therapy (cyclophosphamide, methotrexate, fluorouracil, vinblastine) were retrospectively compared with the clinical data of non-pre-treated patients (n = 28) receiving the same regimen (AC). The two groups of patients were comparable with regard to their risk factors. In the group of women with prior adjuvant chemotherapy only 3 out of 22 had a partial response, lasting 3, 8, and 16 months; the median survival was 50 months. In the group without prior adjuvant therapy 3 complete and 7 partial remissions with a median remission duration of 15.5 months (range 2-54 months) were found; the median survival was 104 months. The percentage of objective responses among the non-pre-treated patients at 36% was almost significantly higher than that of the pretreated women with 14% (p less than 0.1). Responders to chemotherapy after relapse profited in terms of survival within the first 3 years after radical mastectomy, although no statistically significant difference was observed. The survival data shown assume a "shifting" of women from a group with better prognosis to a group with unfavourable prognosis following failed adjuvant chemotherapy.