The antianginal and anti-ischemic properties of isosorbide-5-mononitrate (ISMN) were evaluated in 40 patients with chronic stable angina pectoris in a randomized double-blind parallel-group placebo-controlled study. After 2 weeks’ placebo run-in period the patients were randomized to either ISMN, orally 20 mg 2–3 times daily (titrated) or placebo. They underwent bicycle exercise stress test at the end of the placebo period and after 4 weeks of treatment. Compared with placebo ISMN increased the exercise performance, reduced ST-segment depression, anginal frequency and sublingual nitroglycerin consumption. All these changes were statistically significant. It may be concluded that ISMN is an effective antianginal and anti-ischemic agent in patients with chronic stable angina pectoris.