We evaluated the sweat-patch test for its ability to detect alcohol consumption. During an 8-day study, volunteers drank whisky while wearing sweat-patches that collected sweat continuously at a steady rate. We offered 1.0, 2.0, or 5.0 g ethanol/kg/day to 6 continuous drinkers, and 5.0 g ethanol/kg/day for 2 days to 8 episodic drinkers, and removed sweat patches after 2, 4, 6, and 8 days. The concentration of ethanol in the collected sweat (Cs) rose: (1) progressively with the amount of alcohol consumed: and (2) linearly with the mean concentration of ethanol in the blood (Cb) during the sweat collection period (In Cs = 0.80 In Cb - 1.40; r = 0.93, p < 0.001). The test clearly distinguished drinkers from nondrinkers (Cs < 0.0022 G/L when no ethanol consumed; Cs > 0.0067 G/L when 0.5 G ethanol/kg/day consumed and when Cb > 0.013 G/L). The sweat patch test provides an objective index of drinking behavior with potential applications in clinical practice and research.