Two double-blind multicenter studies compared acebutolol with placebo (acebutolol, N = 121; placebo, N = 116) and with propranolol (acebutolol, N = 186; propranolol, N = 190) in essential hypertension. Acebutolol significantly reduced mean sitting diastolic blood pressure from 99.2 +/- 0.3 mm Hg at baseline to 89.1 +/- 0.9 mm Hg at the end of dose titration (p = 0.001). Significantly more acebutolol patients (65%) achieved therapeutic goal than did placebo patients (28%, p less than 0.01). The reduction in heart rate in acebutolol-treated patients (9.2 bpm) was greater than in placebo-treated patients (1.2 bpm, p = 0.001). The incidence of side effects and the number of patients discontinued because of side effects did not significantly differ between acebutolol and placebo. Acebutolol and propranolol produced comparable reductions in diastolic, systolic, and mean arterial blood pressures (p less than 0.001). At equipotent doses the 13% decrease in heart rate in patients receiving acebutolol was significantly less than the 17% decrease in propranolol patients (p = 0.02). The number of patients experiencing central nervous system (CNS) side effects while receiving acebutolol (N = 50) was significantly less than with propranolol (N = 75, p = 0.001), and significantly fewer acebutolol patients (N = 11) were discontinued because of side effects compared with propranolol patients (N = 29, p less than 0.01). Laboratory, ECG, or chest X-ray results did not differ for acebutolol, placebo, or propranolol. Acebutolol appears to be safe and effective in the management of mild to moderately severe essential hypertension and is better tolerated than propranolol in terms of CNS side effects, with a significantly lesser effect on heart rate.