Eleven patients with essential hypertension were treated with the beta adrenergic blocker, acebutolol. Clinical, systemic, and regional hemodynamic and biochemical studies were performed before and after 4 wk of acebutolol therapy (average doses, 1,200 mg/day.) In 4 patients there was a reduction in mean arterial pressure greater than or equal to 10 mm Hg; there was none in the remainder. Regardless of the blood pressure response, the renin secretory index did not change. Although cardiac output did not change, renal blood flow fell (p less than 0.005) without relation to response of arterial pressure. Supine heart rate decreased (p less than 0.05), so also the responses to upright tilt (p less than 0.01) and isometric exercise (p less than 0.02). These results demonstrate that in those patients with a hypotensive response to acebutolol, the clinical effect was not related to reduced cardiac output or plasma renin activity, further adding to confusion on the mechanism of the lowering of elevated blood pressure by beta adrenergic blockade.