Intestinal absorption of leucine was measured in vivo in rats given ethanol for 7 weeks either through a liquid diet or through drinking water and the results were compared with pair-fed and ad libitum-fed control rats. Total leucine absorption by the entire intestine was not inhibited by ethanol but specific absorption per dry weight of mucosa was increased in the ethanol-fed rats. The intestine of the ethanol-fed rats was shorter and thinner then the ad libitum control rats but its absorptive capacity was maintained by functional adaptation probably by a mechanism similar to that which occurs with semistarvation.