The objective of this study was to investigate the mechanism by which ethanol inhibits intestinal absorption of sugars. In vitro experiments on hamster jejunum have shown that the presence of ethanol in the mucosal solution caused an inhibition of the net transport of water and glucose. There was also a decrease in the intracellular water content and an increase in the intracellular sodium and potassium concentration of the gut tissue. In contrast, the intracellular glucose concentration decreased in the presence of ethanol. These ethanol-induced changes were directly related to the ethanol concentration of the mucosal solution. In the presence of 450 mM (2%) ethanol in the mucosal solution, there was also a significant inhibition of transmural potential difference, estimated glucose metabolism, and both unidirectional fluxes of sodium. The net flux of sodium to the serosal side however did not decrease significantly. These effects of ethanol cannot be fully explained by its osmotic action, and it is suggested that the ethanol-induced reduction in glucose transport could be mainly the result of an interference with the carrier-mediated coupled entrance of glucose and sodium across the brush border. A depression of cellular metabolism could also have played a role in this process.