The purpose of this study was to investigate the effect of protein and dietary fiber levels on the activities of ehanol metabilizing enzymes of the brain in acute and chronic ethanol-treated rats. Male Sprague-Dwley rats were fed on diets containing two levels of protein(7%, 20%)) with two levels of fiber(5%, 105) for 5 weeks. Rats were orally administered 40% (v/v) ethanol(5g/body weight) 90 min before decapitation in the acute ethanol-treated groups and 25% (v/v) ethanol (5g/kg body weight) once a day for 5 weeks in the chronic ethnol-treated groups. Cytosilic alcohol dehydrogenase (ADH) activities were higher than those of mitochondrial ADH. The ADH activities were increased by 20% protein and %% fiber levels in the diet in two fractions , but were decreased by chronic ethanol treatment. Mitochondrial aldehyde dehydrogenase (ALDH) activities did not change by ethanol treatment but were increased by the 20% protein level. However, cytosilic ALDH activities were decreased by chronic ethanol treatment at the 5% fiber level and did not change with protein levels. Both ALDH activities were higher in the 10% fiber groups than the 5% fiber groups. Cytochrome P-450 contents were significantly increased in the chronic ethanol-treated groups but xanthine oxidase (XO) activities did not change. P-450 contents and XO activities were significantly decreased in both the low protein and fiber groups.