Because ethanol inhibits mitochondrial fatty acid oxidation, with substantial accumulation of fatty acids in the livers of female (but not male) rats, and induces microsomal activities, we assessed possible changes in ω-oxidation. To study this, we pair-fed 24 male and 24 female littermate rats of the same age liquid diets containing 36% of energy either as ethanol or as additional carbohydrate for 4 wk. In controls, the microsomal ω-hydroxylation of lauric acid was 28% greater in female than in male rats (p < 0.05). Ethanol feeding significantly increased this activity in both genders (p < 0.01), but the rise in male rats (89%) was significantly higher than that in female rats (24%). This activity was unaffected by the presence of ethanol in the assay. The effects of ethanol were associated with increases in the content of cytochrome P-450 4A1 (as assessed in Western blots by the reactivity against a sheep antibody against P-450 4A1), and more so in male than in female rats. Despite possible competition by ethanol with the hydroxy fatty acid oxidation to dicarboxylic acids through alcohol dehydrogenase, suberic and sebacic acids accumulated significantly in the livers of alcohol-fed male rats. These effects of ethanol and gender on ω-oxidation paralleled those on the hepatic cytosolic fatty acid-binding protein and fatty acid esterification previously reported in similarly treated rats. Dicarboxylic acid products of ω-oxidation have been incriminated as mediators of similar effects by other drugs. Thus the increase in ω-oxidation may compensate, at least in part, for the deficit in fatty acid oxidation caused by the ethanol-induced injury of the mitochondria by promoting fatty acid binding, esterification and oxidation through alternate pathways. This compensatory effect is less efficient in female than in male rats, which may explain why alcohol administration results in a striking and potentially deleterious accumulation of fatty acids in the livers of female but not of male rats. (HEPATOLOGY 1993;18:1247-1253).