This proposal consists of two studies. The objective of the first study is to determine which of isosorbide mononitrate (ISMO) at 20 mg/day or nitroglycerin ointment (NTG) at 15 mg/day results in fewer headaches. The nitrate that is best tolerated will be used in a second study with one main objective: To determine if postmenopausal women with a T-score at the lumbar spine (L1 to L4) between 0 and -2.0 randomized to two years of treatment with intermittent nitrates have a greater increase in spine BMD as compared to women randomized to placebo.