This is a randomized, double-blind, 24-month study. Fifty-five postmenopausal women, age range of 45-65 years, with low bone density will be recruited, with half of the subjects receiving alendronate + 2800 IU of vitamin D once weekly, the other half receiving placebo + 2800 IU of vitamin D once weekly. All study subjects will receive supplemental calcium 1000 mg/day + Vitamin D 400 IU/day. Measurements of microarchitecture will be made in the wrist, ankle, and hip, and the changes in trabecular bone will be assessed at 0, 12 and 24 months. Markers of bone turnover and bone mineral density (BMD) will be used to characterize the cohort and postmenopausal changes in bone turnover and density.