Arterial diameter, blood flow, and vascular resistance of the common carotid artery were studied together with the carotido-femoral pulse wave velocity in men with sustained essential hypertension before and after acute oral administration of either captopril or a hydralazinelike agent, cadralazine. The two drugs caused similar decreases in mean blood pressure and vascular resistance in the carotid area. While cadralazine did not change arterial diameter and pulse wave velocity, captopril caused a significant increase in arterial diameter and a decrease in pulse wave velocity. The study provided evidence that two drugs causing a similar reduction in blood pressure and dilatation of small arteries have different effects on the large common carotid artery. Only captopril caused an enhancement of arterial diameter and distensibility related to the pharmacologic action of the drug on the vascular wall.