The hemodynamic effects of nitroglycerin absorbed transcutaneously from an ointment base were determined in 10 patients with chronic congestive heart failure (9 with ischemic heart disease and 1 with cardiomyopathy). The response was characterized by a decrease in pulmonary capillary wedge pressure from an average of 30 to 19 mm Hg, and an increase in cardiac index from 1.7 to 2.2 liter/min per m2, with concomitant decreases in systemic and pulmonary vascular resistance and an increase in venous capacitance. Mean arterial pressure decreased from 85 to 80 mm Hg, and heart rate remained unchanged. The hemodynamic effects persisted for 3 to 6 hours. These results indicate that nitroglycerin ointment is a hemodynamically potent vasodilating agent with potential value in the therapy of congestive heart failure.