The effects of acute ethanol intoxication on the glycoprotein metabolism of rat liver Golgi apparatus have been investigated. A marked reduction of the galactosyltransferase and sialyltransferase activities was observed in Golgi membranes 6 h after ethanol administration (6g/Kg body wt) together with the retention of glycoproteins in the hepatocyte. Methylpyrazole, an inhibitor of alcohol dehydrogenase, administrated "in vivo" (10 mg/Kg body wt) prevented the ethanol-induced inhibition of both the transferase activities. Acetaldehyde formed "in vitro" unstable and stable adducts with Golgi membrane proteins and with purified galactosyltransferase. These results suggest that the impairment of glycoprotein metabolism at the level of liver Golgi apparatus may be mediated, at least in part, through the acetaldehyde formation during ethanol oxidation.