Whole body retention (WBR) and urinary excretion (UE) of 99mTc-diphosphonate, two complementary methods of measuring the total bone turnover, were performed in 161 normal subjects, 82 women and 79 men, aged 20-70 years. Both WBR and UE were a function of age in the women, whereas there were no age-dependent differences in the men. Between the women and men in identical age groups, the differences did not reach significance. Total body bone mineral (TBBM) was measured by dual photon absorptiometry (DPA) in all subjects. This was done in order to obtain expressions for bone turnover per bone mass as a function of age and sex. This correction emphasized the general picture seen in the raw WBR and UE data: bone turnover was constant in the men throughout life and in the women before the menopause, and only moderate differences were found between the sexes before the age of 50. After this age the mean female values increased sharply. It is noteworthy that none of the postmenopausal subjects showed low turnover values. Our data clearly demonstrate that an increase in bone turnover is part of the pathophysiology of the well-known bone loss in postmenopausal women.