Six post-menopausal women were submitted, at 1 month interval, to oral oestriol treatment for 14-day periods at daily doses of 2 and 6 mg. Blood samples were collected for LH, FSH and PRL measurements (by RIA) every other day during treatments as well as during a 14-day control period. Through the effect on LH levels was questionable, oestriol resulted in a clear and significant, although moderate, gradual decrease of mean FSH levels. At the doses used, which are effective in thetreatment of menopausal symptoms, but are devoid of any proliferative effect upon the endometrium, oestriol failed to induce any stimulatory effect on basal PRL secretion in these post-menopausal women.