Oestrogen treatment of climacteric disorders, chiefly with formulations based on oestradiol or oestrone, which cause much less metabolic disturbance than synthetic oestrogens, is now widely accepted. Physiological replacement requires a blood production rate approaching 0.5 mg/day. Deleterious effects of oestrogen loss are known, but the appropriate scale of long-term prophylaxis with oestrogens is controversial. Evidence for a risk of endometrial carcinoma from unopposed oestrogen therapy is inconclusive but has focused attention on the concurrent use of progestogens, which is rising rapidly but is at present no more than 10%.