The antianginal activity of Molsidomine, a recently developed compound, was studied in 6 patients with stable angina pectoris who attended 3 trial sessions. On different days the patients received single doses of Molsidomine (M; 2 mg), isosorbide dinitrate (ISDN; 5 mg) or placebo (P), in a double blind cross-over manner. All patients performed exercise tests at time 0 (before medication) and 30, 60, 120, 240 and 360 min after drug intake. Tests were performed on a treadmill using the Bruce protocol; the ECG were recorded on 3 channel equipment and was stored on 2 channel magnetic tape (Holter system). No difference between basal values before treatment and on exercise during placebo were observed. At a similar submaximal workload after M and ISDN there was no significant change in heart rate or pressure-rate product, a decrease in systolic blood pressure, a reduction of ST ischemic response between 30 to 120 min after drug intake, and after M alone, a significant decrease in diastolic blood pressure during the 6 hour period. Molsidomine produced clear inhibition of exercise-evoked ischemic ST changes and a long-lasting effect on diastolic blood pressure.