The effect of caffeine (300 mg/70 kg) on cognitive, perceptual and motor functions was investigated both alone and in combination with ethanol (0.75 g/kg) in 68 healthy student volunteers of both sexes. A test battery consisting of standing steadiness, simple and complex reaction time, manual dexterity, numerical reasoning, perceptual speed and verbal fluency was used. Placebos for both drugs were included. Caffeine was administered in decaffeinated coffee immediately after finishing drinking the alcoholic beverage. A peak plasma ethanol concentration of 92 +/- 4 mg/100 ml occurred at 40 min which was not modified by caffeine. Caffeine did not antagonise the ethanol-induced decrement in performance except in the reaction time tests. Caffeine alone caused a significant increase in body sway at 40 min.