To quantify the role of endogenous oestrogen activity in osteoporosis we measured relative metacarpal cortical area (RCA), body mass, serum oestrone, oestradiol, androstenedione, and sex hormone binding globulin (SHBG) in 746 postmenopausal women aged 53 to 76 years, sampled from the general population. The occurrence of fractures and the rate of loss of RCA (delta-RCA) were determined over the previous 9 years. Both RCA and delta-RCA were significantly related to body mass, serum oestrone, oestradiol, and SHBG. The influence of the first three variables appeared to be bone preserving, whereas the latter appeared to be bone wasting. Serum oestradiol, SHBG and body mass proved to have an independent relationship with RCA in multivariate regression analysis. The relationship to delta-RCA was statistically independent for serum SHBG only. Serum androstenedione was unrelated to either RCA or delta-RCA. In the total study population, body mass, serum oestrone, oestradiol and SHBG were not related to the occurrence of fractures over the previous 9 years. In the subgroup of 249 elderly women, aged 65-76 years, SHBG levels were significantly higher for women with type I osteoporotic fractures (vertebral and forearm fractures) as compared to controls. The results suggest a bone wasting influence of SHBG in postmenopausal women, possibly resulting in an increased risk of type I osteoporotic fractures in elderly women.