We assessed blood pressure and neurohumoral factors at rest and during exercise in 10 patients with essential hypertension before and after treatment with the new angiotensin converting enzyme inhibitor, alacepril (25-50 mg day-1). Alacepril significantly lowered mean blood pressure at rest and at the same exercise load as before treatment without affecting heart rate response. The response of plasma renin activity, plasma aldosterone, and plasma adrenaline were not changed by alacepril, but increase of plasma angiotensin II and plasma noradrenaline during exercise were significantly attenuated after alacepril treatment (ANOVA, P = 0.04, both). The change in mean blood pressure during exercise was positively correlated with the decrease in plasma angiotensin II (r = 0.65, P < 0.05). These results demonstrated that alacepril was effective in essential hypertension both at rest and during exercise, suggesting that the antihypertensive effect during exercise might be related to the decrease in pressor hormones, especially in plasma angiotensin II.