To examine whether physical exercise is beneficial in preventing postmenopausal osteoporosis, we measured bone mineral density (BMD) in three distinct groups of healthy postmenopausal Japanese women aged 49-61 yrs: 11 volleyball players (V) and 5 joggers (J), and 9 controls (C) who had not been participating in regular physical activity. BMD was measured at the lumbar spine (L2-L4) and proximal femur using dual energy X-ray absorptiometry, and at the radius using single X-ray photon absorptiometry. Serum levels of estradiol (E2), parathyroid hormone (PTH) and calcitonin were also measured by radioimmunoassay. Osteocalcin was determined by enzyme immunoassay. BMD in the lumbar spine was greater in the V and J groups than in the C group (P < 0.01). The J group had a significantly lower PTH level than the C group. In contrast to weight-bearing bones, we found no significant differences in BMD at the radius among the three groups. BMD at the distal radius was negatively correlated with years after menopause in both the V group and the J group significantly. These results indicate that regular physical exercise has a positive effect on the maintenance of bone mineral in postmenopausal women and that the protective action is localized in skeletal sites used predominantly for the sport without opposing the negative regulation caused by estrogen deficiency in systemic bones.