The objective of the present study was to investigate the acute effects of alcohol on blood flow volume and velocity, on wall motion of superficial large arteries, and on systemic hemodynamics in humans. In 10 healthy volunteers small doses of alcohol were administered either orally (0.3 g/kg in 250 mL water) or intravenously (7.5 mg/kg/minute in 250 mL saline in 40 minutes). The effects of alcohol were compared with those of saline 250 mL infused for 40 minutes (6.25 mL/min). Blood velocity and systodiastolic changes of wall diameter were measured in the common carotid, femoral, and brachial arteries simultaneously with cardiac output and finger blood pressure. Skin temperature was measured at the cheek, hand, and toe. Ethanol administration caused a transitory blood pressure increase accompanied by a rise in peripheral resistances at 20 minutes. Arterial blood flow was not changed by either mode of alcohol administration at any of the measurement sites. However, this result was achieved through different compensatory mechanisms in each artery. In fact, mean carotid diameter increased after both oral and intravenous ethanol administration but remained unchanged at the brachial and femoral level. Mean blood velocity was reduced after alcohol administration at the carotid but was unchanged at the brachial and femoral level after oral or intravenous alcohol administration. Skin temperature increased 20 minutes after alcohol administration at all sites. This study shows that although acute alcohol administration does not change blood flow in superficial large arteries, it causes different autoregulatory local responses of vessel walls.