Molsidomine was shown to have a strong pain-relieving action in 22 coronary patients investigated one hour after oral intake of 2 mg of the substance. During comparable maximal exercise load the ST interval lowering was reduced from an average of 0.22 mV to 0.09 mV (P less than 0.0005). At the termination of exercise it was still reduced from 0.23 mV to 0.12 mV (P less than 0.0005). At the same time the exercise tolerance increased from 570 to 717 Watt-minutes (P less than 0.0025). Pectanginal complaints were clearly reduced at the same exercise loads, 11 patients became symptom-free at the same load. Even when exercise loading was stopped at higher loads a decrease of the severity of angina pectoris could be shown. Seven patients became symptom-free at that stage. The heart rate was not influenced markedly at rest and during exercise. Systolic blood pressure was reduced from 135 mm Hg to 118 mm Hg (P less than 0.0005), and in comparable submaximal loads from 177 to 165 mm Hg (P less than 0.005).