Cutaneous absorption of nitroglycerin is a well documented phenomenon which may have unique advantages for the sustained prophylaxis of angina pectoris. Therefore, the authors examined the effects of nitroglycerin ointment and placebo on exercise capacity in 14 patients with angina pectoris. Nitroglycerin ointment produced a significant increase in exercise capacity which persisted for at least 3 hr. Concomitant sustained changes in systolic blood pressure and resting heart rate were observed. Electrocardiographic evidence of myocardial ischemia was significantly reduced. Chronic administration in 6 patients did not reduce the effects of either nitroglycerin ointment or sublingual nitroglycerin. Nitroglycerin ointment appears to be a truly long acting nitrate. While evidence of nitrate toxicity or tolerance was not observed in the present study, additional information is required before the widespread use of this agent can be recommended.