Changes in blood pressure and heart rate after exercise, left ventricular wall thickness, ejection fraction and left ventricular mass were examined by echocardiography before and at the 8th week administration of captopril (37.5－75.0 mg/day) in 11 patients with essential hypertension. The blood pressure showed a gradual and significant decrease from the second week of captopril administration, but the heart rate remained unchanged. No changes were observed in the blood pressure or heart rate after exercise, nor before, during and after the administration of captopril. In the echocardiographic examinations, the wall thickness decreased significantly from 12.1 ± 2.1 mm before administration to 10.6 ± 1.5 mm at the 8th week of' administration in the interventricular septum, from 11.2 ± 1.8 mm to 10.1 ± 1.5 mm in the left ventricular posterior wall, and the left ventricular mass in parallel decreased from 266 g to 218 g. In 7 patients, whose wall thickness was 12 mm or more, the thickness of the septum decreased significantly from 13.9 ± 1.2 mm to 11.7 ± 2.1 mm and that of the left ventricular posterior wall from 12.6 ± 1.5 mm to 10.6 ± 1.8 mm. Captopril administration produced regression of cardiac hypertrophy in patients with essential hypertension within a period of only 8 weeks.