Ten male subjects were given alcohol by intravenous infusion and maintained at a constant blood alcohol level. The rate of alcohol metabolism was measured before and after an oral dose of fructose (100 g), as the amount of alcohol required to maintain the steady state. The mean rate of alcohol metabolism increased by 80% after fructose but there was considerable variation among the subjects, which was related to their plasma fructose concentrations. Blood lactate increased after fructose to a greater degree than blood pyruvate, resulting in a significant increase in [lactate]/[pyruvate] ratio. Since fructose increased the [lactate]/[pyruvate] ratio when it increased alcohol metabolism, the action of fructose cannot be explained by a decrease in the liver cytoplasmic [NADH]/[NAD] ratio and some other mechanism must be sought.