AIM: To study the expression and activity of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) in rats with ethanol-induced liver injury and their relation with liver damage, activation of nuclear factor-KB (NF-кB) and tumor necrosis factor-α (TNF-α)expression in the liver.METHODS: Female Sprague-Dawley rats were given fish oil (0.5 mL) along with ethanol or isocaloric dextrose daily via gastrogavage for 4 or 6 wk. Liver injury was assessed using serum alanine aminotransferase (ALT)activity and pathological analysis. Liver malondialdehyde (MDA), nitric oxide contents, iNOS and eNOS activity were determined. NF-KB p65, iNOS, eNOS and TNF-αprotein or mRNA expression in the liver were detected by immunohistochemistry or reverse transcriptase-polymerase chain reaction (RT-PCR).RESULTS: Chronic ethanol gavage for 4 wk caused steatosis, inflammation and necrosis in the liver, and elevated serum ALT activity. Prolonged ethanol administration (6 wk) enhanced the liver damage. These responses were accompanied with increased lipid peroxidation, NO contents, iNOS activity and reduced eNOS activity. NF-кB p65, iNOS and TNF-α protein or mRNA expression were markedly induced after chronic ethanol gavage, whereas eNOS mRNA expression remained unchanged. The enhanced iNOS activity and expression were positively correlated with the liver damage, especially the necro-inflammation, activation of NF-кB, and TNF-α mRNA expression.CONCLUSION: iNOS expression and activity are induced in the liver after chronic ethanol exposure in rats, which are correlated with the liver damage, especially the necro-inflammation, activation of NF-KB and TNF-αexpression. eNOS activity is reduced, but its mRNA expression is not affected.