The effect of alcohol on exercise-induced changes in serum glucose, serum free fatty acids, and serum insulin was studied in healthy male volunteers by performing an exhaustive ergometer exercise: (1) followed by alcohol intoxication (induced by 1.5 g of alcohol/kg of body weight); (2) during alcohol intoxication (induced by 0.8 g of alcohol/kg of body weight); and (3) during hangover (13 hr after a dose of 1.5 g of alcohol/kg of body weight). Acute alcohol intake immediately before exercise inhibited the exercise-induced increase in mean serum glucose concentration and caused a mild decrease in serum glucose levels during recovery from exercise. Exercise during hangover also resulted in decreased glucose levels during recovery from exercise. Alcohol administration immediately before or after exercise inhibited the postexercise increase in mean serum free fatty acids concentration. This was not seen during hangover, when blood alcohol concentration had already reached 0. In conclusion, alcohol interferes with the metabolism of carbohydrates during and after anaerobic exercise by decreasing the availability of circulating glucose. Furthermore, during recovery from exercise, alcohol decreases the supply of free fatty acids for the body.