The antihypertensive effect of acebutolol, a new cardioselective beta-blocking drug, is studied in 31 patients with mild essential hypertension. Administration of acebutolol (2,000 mg) in 48 hours produced a significant decrease in blood pressure, heart rate, plasma renin activity (P.R.A.) and an increase in systolic time intervals (pre-ejection period and isovolumetric contraction time). The blood pressure drop is highly correlated to the initial P.R.A. values, but is not related either to the initial heart rate, or to the systolic time intervals values.