To test these hypotheses we will execute 2 trials both of which include postmenopausal women, aged 50 and older, with BMD T scores at the lumbar spine between 0 and -2.0. We will exclude subjects with prior osteoporotic fractures or OP by BMD testing, subjects with current metabolic bone or cardiovascular disease, subjects taking treatments for OP, subjects with migraine headaches, and subjects with known hypersensitivity to nitrates. We will use computer generated randomization to allocate subjects to treatment assignments. To avoid bias the studies will be double-blind. The first study, which uses a crossover design, will recruit 22 subjects who will be randomly assigned to each of NTG ointment and ISMO for one week. In between treatments there will be a two week wash out period. Subjects will rate headaches on a daily basis using a visual analog scale and for each subject I will calculate the mean headache score over the 7 day treatment period for both treatments. We will then calculate the mean headache score (considering all subjects) for NTG and the mean headache score for ISMO. We will compare the mean headache scores for both treatments and the nitrate preparation that is best tolerated (lowest mean score) will be used in a second placebo controlled study (the main study) whose primary objective is to assess the effects of intermittent nitrates on spine BMD (L1 to L4) in 280 postmenopausal women. To limit differential drop out due to headaches among subjects randomized to nitrates, the main trial will follow a run-in phase during which all subjects will receive nitrates for one week. Only those subjects who do not have headaches resulting in discontinuation of the study medication during the nitrate run-in phase will enter the main study.