1. During a 28-day treatment period, 10 healthy volunteers in a cross-over, double-blind study received at random 200 mg of either acebutolol or labetalol twice a day. Each treatment period was followed by administration of a placebo over an equal length of time. 2. Only acebutolol reduced heart rate measured in the supine position significantly at rest, whereas acebutolol and labetalol reduced it significantly after exercise on the treadmill. 3. Only acebutolol lowered humeral pressure at rest but not after exercise. Neither drug produced a change in blood pressure in the ankle or in the first toe at rest or after exercise. 4. Blood flow measured by plethysmography was increased by labetalol in the calf by comparison with placebo and in the first toe by comparison with placebo and acebutolol. 5. Labetalol lowered peripheral resistance significantly in comparison with placebo in the calf and first toe. Acebutolol tended to lower the resistance insignificantly in the calf but to increase resistance in the first toe.