This study examines the effects of increasing doses of nifedipine on exercise-induced ST-segment depression in patients with severe typical stable angina pectoris. 10 patients underwent four 1 -week treatment periods in a single-blind clinical trial. These were nifedipine 0, 30, 60, and 90 mg in divided doses daily. At the end of each week a maximum exercise test was performed using 16 precordial electrocardiographic leads and the ST-segment changes measured immediately after exercise. In 4 patients nifedipine produced no effects on these electrocardiographic parameters; 4 patients improved and 2 deteriorated. Thus, a dose of nifedipine, effective in 1 patient, can have opposite effects in another.