Calcium balance as a function of both intake and absorption of calcium fromthe diet was measured 274 times in 168 normal perimenopausal women, and comparisons made between groups of women segregated according to menopausal and estrogen therapy status. As previously reported, there is a statistically significant positive correlation between calcium balance and both calcium intake and calcium absorption. In 207 studies in premenopausal women calcium balance averaged -0.0199 gm/day, whereas in 41 studies in postmenopausal women untreated with estrogen, calcium balance averaged -0.043 gm/day (p less than 0.02). The balance difference was due approximately equally to decreased absorption from the diet and to increased urinary excretion. Twenty-six estrogen-treated postmenopausal women exhibited balance performance indistinguishable from that of the premenopausal group. In 16 women who were studied twice, 5 years apart, and who went through menopause between studies, calcium balance shifted by -0.0307 gm/day (p less than 0.05) as compared with 72 women also studied twice, but without change in menstrual status, in whom mean balance did not change significantly. Calcium intake requirement for zero balance was calculated for both the estrogen-replete and estrogen-deprived groups. Premenopausal and treated postmenopausal women exhibited an intake requirement of 0.990 gm/day Ca, whereas the untreated postmenopausal women had an apparent requirement of 1.504 gm/day (p less than 0.01). We conclude that there is a specific, estrogen-related shift in calcium performance across menopause and that the reason for the positive effect of estrogen on balance and intake requirement is a combination of enhancement of intestinal absorption efficiency and improved renal calcium conservation.