Women with depression and low BMD (negative 1.5 SD below peak bone mass at the spine and/or hip) will enter a 12-month, placebo-controlled, clinical trial where they will be randomized either to blind alendronate 70 mg once a week (Group C) or blind placebo once a week (Group D). In addition to alendronate 70 mg once a week or placebo once a week, women in Groups C and D will also receive daily 500 mg of elemental calcium and 400 IU of vitamin D. DEXA determinations will be performed at Screening, Month 0, Month 6, and Month 12. Determination of biochemical markers of bone turnover and endocrine parameters relevant to depression will be performed at 0, 3, 6, 9 and 12 months. An exercise substudy will be performed at 0, 6, and 12 months. The collection of a DNA sample will also be performed at one of the above visits.