Captopril, an orally active inhibitor of angiotensin converting enzyme, was administered for 12 months to 20 patients with mild or moderate essential hypertension who initially responded favourably to this pharmacological treatment. Captopril induced a significant reduction in blood pressure which remained unmodified throughout the study. This fall in blood pressure was mainly due to a significant decrease in total peripheral vascular resistance, since no change in cardiac output was observed. Simultaneously, there was no significant change in left ventricular anatomy and performance evaluated by echocardiographic technique.