OBJECTIVE: To determine whether female marmosets undergo a reduction in bone mineral density following ovariectomy or socially induced hypoestrogenic anovulation. RESULTS Chronic reduction in estrogen causes a reduction in bone mineral density and increase in osteoporosis in all species in which it has been studied. In marmosets, socially subordinate females regularly become anovulatory and may remain hypoestrogenic for extended periods of time. To determine whether these animals might possess a mechanism to protect them from the deleterious skeletal consequences of hypoestrogenism, we examined the effect of ovariectomy-induced or socially induced hypoestrogenism on bone mineral density in marmosets. No differences in bone minderal density were found between ovary-intact and ovariectomized females, or between dominant and subordinate females. A longitudinal study also failed to reveal any effects of ovariectomy on bone mineral density. Thus, marmosets may possess a unique adaptation protecting them from hypoestrogen-induced bone loss, and might provide a novel model for the investigation and treatment of osteoporosis. FUTURE DIRECTIONS We plan to confirm and extend our preliminary findings using a larger sample size, and to begin to investigate the possible biochemical and cellular mechanisms by which estrogen depletion does not cause bone loss in female marmosets. KEY WORDS dual-energy x-ray absorptiometry, skeletal system, osteoporosis