Verapamil was evaluated as an antihypertensive agent in a pilot study. Intravenous administration of 0.1 mg/kg, followed by constant infusion of 0.0035 mg/kg min, reduced both systolic and diastolic blood pressure significantly; the maximal average decrease of 23/16 mm Hg occurred after 5 min. The resting pulse rate rose during infusion and prolongation of the atrio-ventricular conduction time was a constant finding. After the initial drop in blood pressure, a rise toward control levels was observed, despite an increase in the infusion rate. Five patients received oral treatment with verapamil 320-640 mg daily for 7 weeks. In four of the five patients a blood pressure reduction was obtained (mean: 14/12 mm Hg), but normotension was not achieved in any of them. In contrast to the acute studies, the atrio-ventricular conduction time showed no change and a decrease in resting pulse rate was noted. Two patients experienced sensations of heat and reddening of face during treatment. It is concluded that verapamil has a rather modest antihypertensive effect and it is not suitable for the treatment of arterial hypertension.