As a result of recent advances in our understanding of the role of nitric oxide and endothelial-derived relaxing factor (EDRF) in vascular control, physicians now have the potential to overcome the loss of EDRF effect by administering nitrates. Nitrates are converted to nitric oxide, resulting in vasodilator effects that improve the myocardial oxygen supply-demand imbalance responsible for myocardial ischemia. This discovery has resulted in a renewed interest in the nitrates for the treatment of ischemic syndromes, particularly chronic stable angina pectoris. Over the past 2 years, an important new formulation of nitrate has become available--isosorbide-5-mononitrate. Three different mononitrate formulations are available in the United States: Ismo tablets in December 1992; followed over a year later by Monoket tablets, available since June 1993; and Imdur extended-release tablets, available since August 1993. Although the mononitrates share the same generic name, they are not similar in regard to their formulations, which suggests the need for future studies designed to explore any clinical differences.