Acebutolol (ABL) and hydrochlorothiazide (HCT) were compared in patients with mild to moderate essential hypertension and low or normal peripheral renin activity. ABL reduced mean supine blood pressure from 151/97 to 140/87 mm Hg and HCT reduced the mean supine blood pressure from 153/98 to 143/92 mm Hg. ABL reduced heart rate from 73 to 67 beats/min; during HCT therapy it rose from 74 to 77 beats/min. Although the same proportion of patients achieved normal diastolic pressures with ABL (11/19) and with HCT (10/19), tension-time indices were lower during ABL than during HCT therapy. The average daily dose was 621 mg of ABL and 168 mg of HCT. Stimulated peripheral renin activity increased with HCT and was the same or lower with ABL. ABL did not induce adverse effects on serum potassium or uric acid. ABL was as effective in lowering blood pressure HCT but induced larger reductions in tension-time index as a result of the lowerered heart rate.