Medical ovariectomy with goserelin is an alternative to surgical oophorectomy. To evaluate the relationship between tumor regression and endocrine changes induced by therapy, 40 premenopausal patients with advanced breast cancer were given 3.6 mg of goserelin subcutaneously fortnightly for the first 4 doses and every 28 days thereafter. We have made a particular analysis of the clinical and endocrine profile of responsive patients. Objective responses were observed in 17 of the 38 evaluable patients (45%), 6 cases achieving complete remission. Serum estradiol was suppressed in castrated women, although there was a tendency towards an increase in serum follicle-stimulating hormone over time. No statistically significant difference was observed in the hormonal profiles of patients experiencing a complete or partial response. Our experience confirms that goserelin is as effective as oophorectomy and that there is a clear correspondence between clinical response and drug-induced estrogen suppression.