Fifty-seven patients with large but potentially operable primary breast cancer were treated with primary medical therapy rather than initial mastectomy, using chemotherapy (15) or endocrine therapy (42) with the tumour remaining in situ. Of patients treated with chemotherapy, one (7%) achieved a complete remission, and eight (53%) a partial response (overall response rate 60%). Only one patient had progressive disease while on chemotherapy. Of patients who received endocrine therapy, one (2%) achieved a complete response, and 19 (45%) a partial response (overall response rate 47%). Two patients progressed on endocrine therapy. Only 10 patients have so far had a subsequent mastectomy (18%), and 17 (30%) have had radiotherapy and/or conservative surgery. The rest are still on medical therapy. With a median follow-up of 19 months (range 6-42 months) only two patients have had a local recurrence after being disease-free and none have developed uncontrollable local recurrence. Eight (14%) have developed distant metastases and four (7%) have died of metastatic disease. Primary medical therapy may offer an effective alternative to mastectomy for patients with operable breast carcinomas too large for conservative surgery and merits further study.