Long-term therapy with (7 alpha,17 alpha)-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one (Org OD 14; tibolone, Livial) has no influence on the endometrium in post-menopausal women. This was concluded from endometrial biopsies taken from 39 post-menopausal women treated with 2.5 mg/day for periods of from 3 months to 5 years 11 months at three centres. These results accord with the data published so far on 129 women who have been treated for up to 2 years. A review of the data relating to a total of 168 patients treated with Org OD 14 is presented. The endometrial pattern observed at the start of therapy showed no change during treatment in 90% of patients. In 15 cases slight proliferation was apparent after treatment, this being a similar pattern to that seen in the initial days of a normal cycle. In a considerable number of patients no tissue could be obtained, indicating an atrophic pattern. The picture following Org OD 14 therapy was the same as that observed in untreated normal post-menopausal women.