ESTRADIOL DIPROPIONATE has an apparent superiority over other parenteral estrogens in the treatment of menopausal symptoms. It will relieve and maintain patients symptom free with treatment once a week or, in the majority of cases, with treatment every two or three weeks (1,2). Estrone is relatively inefficient in that it is less potent and must be administered much more frequently. A direct comparison of the two substances in a group of patients demonstrated that estradiol dipropionate was the more effective of the two (2). In the experimental animal estradiol dipropionate also has a more prolonged action than equal amounts of estradiol benzoate (3). There has been, to the author's knowledge, no direct comparison of these two substances in the human being. It was thought, therefore, that the following data on this subject should be of interest.