The effects of fructose and glucose on the metabolic changes induced by ethanol and on the intensity of alcohol intoxication and hangover were studied in 109 healthy male volunteers. After 10 hours of fasting, the subjects were given 1.75 g of ethanol per kg body wt during 3 hours under controlled laboratory conditions. Fructose or glucose were adminstered either simultaneously with ethanol or 12 hours later during the hangover period. The intensity of alcohol intoxication and hangover were estimated 10 times during the experimental period of 20 hours using subjective and objective rating scales. Sequential determinations of blood ethanol, acetaldehyde, glucose, lactate, free fatty acids, triglycerides, ketone bodies and capillary blood acid-base balance were also made during the experiment. Under these experimental conditions neither fructose nor glucose had any significant effect on the intensity of alcohol intoxication and hangover. The sugars also had no significant effect on the rate of ethanol elimination or on the blood acetaldehyde concentration during the course of the experiment. Blood glucose concentration was decreased and blood lactate, free fatty acid and ketone body concentrations were increased during the hangover period in the subjects who had been given only ethanol. These subjects also had a marked metabolic acidosis during hangover. Glucose and fructose significantly inhibited the metabolic alterations induced by ethanol. In this respect fructose was more effective than glucose. The results indicate that both fructose and glucose effectively inhibit the metabolic disturbances induced by ethanol but they do not affect the symptoms or signs of alcohol intoxication and hangover. The results support the view that hangover is not directly related to the metabolic effects of ethanol or to its metabolic products.