Rates of ADP stimulated respiration for various substrates were determined in mitochondria isolated from the livers of female Sprague-Dawley rats following 8 weeks of treatment with daily swimming, ethanol consumption, or both. All rats were fed an American Institute of Nutrition (AIN) type liquid diet with the ethanol treated rats receiving 35% of the calories as ethanol. Chronic exposure to ethanol depressed both state 3 respiration with glutamate as a substrate and cytochrome oxidase activity. Respiratory control ratios and P:O ratios, however, were unaffected by the ethanol exposure. Exercise alone had no effect on hepatic mitochondrial function. There were also no significant alterations in oxidative function of hepatic mitochondria from rats which were endurance-trained by swimming while receiving the ethanol diet. This lack of alteration in mitochondrial function was in spite of the fact that these rats consumed an identical amount of ethanol as those which incurred mitochondrial dysfunction. These results indicate that regular exercise has the potential to attenuate the ethanol induced decline in hepatic mitochondria.