The effectiveness of nitroglycerin ointment in vasospastic angina pectoris at rest was evaluated in 10 patients selected for study. The study was performed after a 24 hour control period, and a randomized single-blind crossover experimental design was followed. Two percent nitroglycerin ointment (15 mg) or placebo ointment was administered every 6 hours for a period of 48 hours each; the first treatment period was followed by a second in which each preparation was used for a 24 hour period. All patients were hospitalized in the coronary care unit; an objective evaluation was carried out using a multichannel electrocardiographic recording to assure recognition of the painless ischemic episodes. Coronary angiography showed critical stenosis of one or two vessels in 9 of the 10 patients; spasm was demonstrated in 3. Results of the ergonovine test were positive in nine of nine patients. Nitroglycerin ointment produced a significant reduction in the mean daily number of episodes during the first (12.5 +/- 3.9 versus 0.5 +/- 0.4, p less than 0.02) as well as the second treatment period (10.6 +/- 3.8 versus 0.6 +/- 0.4, p less than 0.02). These results demonstrate that nitroglycerin ointment provides effective, long-lasting protection against angina due to coronary spasm.