This study compared the concentration of ethanol, both absolute and relative to water content, in sweat and blood. Ten male volunteers consumed approximately 13 mmol (kg body weight)-1 of ethanol. Blood and sweat samples were collected approximately 1, 2 and 3 h following ingestion. Sweat was collected following pilocarpine iontophoresis using an anaerobic technique that prevented ethanol evaporation. In addition, the water content of sweat and blood samples was determined. The correlation between sweat and blood ethanol, expressed in mmol l-1, was r = 0.98. The slope of the relationship was 0.81. When corrected for the water content in each sample, and expressed as mmoles per litre of water, the correlation remained very high (r = 0.97) while the slope increased to 1.01. These results suggest that rapid and complete equilibrium of ethanol occurs across the sweat gland epithelium.