Calcium antagonists are vasodilators and, therefore, they decrease the peripheral vascular resistance. Acute vasodilation invokes a reflex increase in sympathetic activity that results in positive chronotropic and inotropic effects. These acute effects have been demonstrated both in patients with hypertension and subjects with normal blood pressure values. A theoretic objection to the use of nifedipine as monotherapy in patients with chronic hypertension was that calcium channel blockers would invoke a chronic sympathetic response and, in particular, chronic tachycardia. In this study, the effects of calcium antagonists on ambulatory blood pressure were investigated in patients with essential hypertension who had no evidence of target organ damage. Direct arterial blood pressure measurements, monitored continuously over 24 hours, showed that nifedipine significantly reduced systolic and diastolic blood pressures throughout the day and at night. The variability in blood pressure values was not altered by nifedipine therapy, nor were there significant changes in heart rate. Estimations of left ventricular mass also demonstrated that successful control of blood pressure with nifedipine monotherapy resulted in a significant reduction in the left ventricular mass similar to that achieved with beta blockers and diuretics. Thus, nifedipine may be used effectively as monotherapy in patients with essential hypertension, controlling blood pressure throughout the day and at night. Calcium antagonists are, therefore, useful drugs in the management of hypertension and, in light of the findings reported herein, should be seriously considered as initial therapy.