Although it is well known that chronic ethanol abuse produces sexual dysfunction and impaired spermatogenesis, the mechanisms of ethanol-induced testicular alterations are not fully explained. Therefore, the aim of this study was to investigate the mechanisms of testicular oxidative damage in rats given drinking water containing 3% ethanol for 8 weeks. Control rats were pair-fed with saccharose. The mean daily ethanol intake was 4.05 g kg(-1), corresponding to the consumption of 41 of wine (10% alcohol) or 0.71 of whiskey (40% alcohol) by a man of 70 kg body wt. Exposure to ethanol caused a significant depletion in the testicular levels of glutathione (GSH), protein containing sulfhydryl groups, tocopherol and ascorbic acid, and an increase in the concentrations of malondialdehyde (index of lipid peroxidation) and carbonyl proteins (index of protein oxidation). Other effects were decreases in the concentration of adenosine 5'-triphosphate and in the activity of glutathione peroxidase, and an increase in the activity of alcohol dehydrogenase. In summary, this study shows that in the rat, daily consumption of ethanol in the drinking water increases lipid and protein oxidation. In addition to impaired antioxidant defence, an imbalance in energy production may also play a role in the toxic reaction to alcohol.