Clinical efficacy of 5 mg per 24 hours transdermal nitroglycerin was studied in a placebo controlled, randomized, double-blind crossover trial, with three days wash-out period at the beginning, in 40 patients with chronic stable angina pectoris during two periods of 14 days. Assessment was carried out by means of a diary method, by the multistage treadmill exercise test, five hours after dosing, and by 24-hour ambulatory ECG recordings. Nitroglycerin patch demonstrated significant improvement of exercise tolerance comparing to placebo, in exercise time to the onset of angina pectoris and ST-segment depression of greater than or equal to 1.0 mm (+45% and +47%), in maximum walking time (+13%), as well as in diminished severity of maximum angina (-38%), in lower maximal ST-segment depression (-32%) and in faster recovery of ST-depression 3 and 6 minutes after the test (-28% and -44%). Nitroglycerin patch showed 33% less angina attacks, mainly severe and moderate, resulting in 37% less sublingual nitroglycerin consumption. A significant fall in the number of ST-segment depression episodes of 1.5 mm or more (-60%) was shown in the 24-hour ECG. All these changes were confirmed to be significant compared to placebo values, at a level of P less than 0.01, by multivariate analysis. This study revealed a positive effect of low dose nitroglycerin patch on improvement of exercise functional capacity and signs of myocardial ischaemia after 14 days of continuous therapy.