In 30 patients with mild to moderate essential hypertension and high-normal left ventricular (LV) mass, the effects of treatment for 6 months with amlodipine (5 to 10 mg every morning) versus diltiazem-sustained release (SR) (90 to 180 mg twice daily) on 24-hour blood pressure (BP), plasma catecholamines, and echocardiographic estimates of LV mass and function were evaluated. Both amlodipine and diltiazem caused stable, persistent BP reduction over 24 hours with no evidence for a "peak" effect. For a similar decrease in diastolic BP, amlodipine caused a significantly larger decrease in systolic BP. Amlodipine decreased BP by lowering total peripheral resistance, whereas diltiazem caused small decreases in both total peripheral resistance and cardiac index. Both calcium antagonists caused modest but significant decreases in supine and standing plasma catecholamines. LV wall thickness and LV mass decreased significantly over the 6 months of follow-up: -6 +/- 2 with diltiazem and -10 +/- 2 g/m2 with amlodipine. In patients taking amlodipine, the decrease in LV mass correlated significantly with the decrease in plasma norepinephrine. In contrast to rapid-acting calcium antagonists, both amlodipine and diltiazem-SR cause smooth BP control and an appropriate decrease in LV mass without activation of the sympathetic nervous system.