Rates of change in bone mineral density (BMD) at four skeletal sites were measured in 288 healthy postmenopausal women (41-71 years) who were participants in a 2-year calcium supplement trial. Mean calcium intake from food and supplements was 719 +/- 299 (sd) mg/day during the study. Annualized change in spine (L2-4) BMD, adjusted for body size, dietary calcium intake, treatment group and smoking was -2.24% +/- 2.07% (sd) in women who were 1 to 2 years postmenopausal and declined in women through 5 years after menopause. The rate of change in women who were 6 or more years postmenopausal was -0.96% +/- 2.96%. Mean adjusted change in heel BMD in all women was -1.16% +/- 3.26%. At the femoral neck and radius there was no significant adjusted change in BMD in the group as a whole (femoral neck -0.24% +/- 2.55%; radius -0.14% +/- 2.24%), and the rate of bone loss was not detectably accelerated in women closest to menopause. Rates of bone loss in the subset of subjects who received no calcium supplementation tended to be greater at all skeletal sites.