In contrast to all other oestrogens examined thus far oestriol hemisuccinate (12 mg/day) did not prevent bone loss in 28 postmenopausal women. The average bone loss, however, was somewhat less than expected from placebo studies, while the bone loss achieved by a group taking 4-6 mg/day was equal to that achieved by previous placebo groups. To be an effective agent for prevention of post-menopausal osteoporosis oestriol would have to be prescribed in daily doses considerably in excess of 12 mg.