At this point, I think I should point out that it now seems possible that postmenopausal osteoporosis, like smallpox and poliomyelitis, can be eradicated. Although full replacement doses of oestrogen prevents progression of the disease in women who have already lost a great deal of bone, this is like locking the stable door after the horse is gone. Present evidence is that smaller doses will probably suffice to prevent loss of bone at the menopause: mestranol 20 microng (Aitken et al, 1973) or conjugated oestrogens USP 0.625 mg (Meema, Bunker and Meema, 1975). The minimal prophylactic osteotrophic dose has not yet been determined since the two doses indicated were the smallest tested. These two studies provide hope that a dose can be found which will prevent postmenopausal osteoporosis without necessarily producing endometrial hyperplasia. It is very likely that the prevention of bone loss by small, prophylactic doses of oestrogen will reduce the number of fractures of vertebrae, wrists and hips so common in postmenopausal women and will reduce the mortality presently caused by hip fractures.