Etheno adducts in DNA are formed from the carcinogens vinyl chloride and urethane, and also from products of lipid peroxidation (LPO), such as trans-4-hydroxy-2-nonenal. Using an ultrasensitive detection method, the formation of etheno-DNA adducts in the liver was demonstrated in LEC rats (a strain with hereditary abnormal copper metabolism) that develop hepatitis and hepatocellular carcinoma. Wilson's disease and primary haemochromatosis are human genetic disorders that cause copper or iron accumulation resulting in a high risk for primary liver cancers. Levels of etheno adducts were also significantly elevated in the liver of these patients. In a group of male and female volunteers kept on a controlled diet, the effect of dietary fatty acid composition on the endogenous formation of lipid peroxidation-derived DNA adducts was determined in DNA from white blood cells. Dietary omega-6-polyunsaturated fatty acids greatly increased LPO-derived etheno-DNA adducts in vivo, in females. Thus, exocyclic DNA adducts are promising biomarkers for elucidating the effect of dietary fat intake, oxidative stress and protective dietary antioxidants on endogenous DNA damage and thus may provide a possible mechanistic link with elevated risk for diet-related cancers.