The hemodynamic effects of nitrendipine have been studied at rest and during exercise in eight patients with mild to moderate essential hypertension. Acutely, nitrendipine (20 mg) induced at rest a decrease in arterial blood pressure (from 194/100 to 151/78 mm Hg) and an increase in heart rate (from 81 to 101 beats/min); the cardiac output was unchanged and the systemic vascular resistances fell by 30%. Similar changes were observed during exercise, i.e., a decrease in arterial blood pressure (from 245/106 to 204/87 mm Hg) and in systemic vascular resistances (-25%) with an increase in heart rate (from 133 to 142 beats/min). After chronic treatment during 55 days (average daily dose was 46 mg), the hypotensive effects of nitrendipine were similar, although less marked, both at rest and during exercise; the tachycardia noted after acute intake disappeared after chronic therapy. The addition of atenolol (100 mg) at the end of the chronic study in six patients further reduced arterial blood pressure at rest (138/80 mm Hg) and during exercise (180/91 mm Hg); the heart rate decreased to 60 beats/min at rest and 94 beats/min during exercise. These data show that nitrendipine is a potent antihypertensive agent that induces an important fall in the systemic vascular resistances both at rest and during exercise; during chronic therapy, these antihypertensive effects were maintained while the reflex tachycardia disappeared. The addition of atenolol during chronic therapy contributed to the normalization of the resting and exercise arterial blood pressures in nearly all patients.