Although several epidemiological studies have shown an association between alcohol consumption and high blood pressure, the mechanisms involved in the pressor effect of alcohol are not clear. We hypothesized that alcohol might increase blood pressure at least in part by increasing sympathetic nerve activity. In a double-blind, placebo-controlled study of seven normotensive subjects (mean age +/- s.e.m. 24.0 +/- 1.5 years), we investigated the effects of oral administration of alcohol (0.75 g/kg body weight, diluted in orange juice) or vehicle on arterial blood pressure, heart rate and muscle sympathetic nerve activity, measured directly in the peroneal nerve by microneurography. Plasma ethanol levels increased from 0 (control) to a range of 47.7 +/- 7.6 to 53.3 +/- 5.0 mg/dl 30 min after alcohol intake. This increase in plasma ethanol was accompanied by a significant increase (P less than 0.05) in mean blood pressure, heart rate and sympathetic nerve activity. The vehicle did not affect any of these parameters. Our data suggest that acute oral administration of a moderate dose of alcohol induces a pressure effect through activation of sympathetic nervous outflow.