To assess DNA damage caused by lipid peroxidation due to copper and iron storage disorders in the human liver, the formation of the etheno adducts 1,N6-ethenodeoxyadenosine (epsilon dA) and 3,N4-ethenodeoxycytine (epsilon dC) was measured in liver DNA from normal subjects and from patients with Wilson's disease (WD) and primary hemochromatosis. The mean epsilon dA and epsilon dC levels per 10(9) parent nucleotides in normal liver were 19.3 +/- 4.9 and 27.5 +/- 10.0, respectively. The mean epsilon dA and epsilon dC levels per 10(9) parent nucleotides in WD were 61.03 +/- 7.95 and 91.50 +/- 36.02, and in primary hemochromatosis, they were 46.62 +/- 32.83 and 64.32 +/- 11.55, respectively, two to three times higher than those in the normal liver. The etheno adduct levels were highly correlated with the copper content of the liver in the normal and WD samples. This study demonstrates for the first time the formation of promutagenic etheno adducts in humans in association with copper and iron storage-induced lipid peroxidation. Thus, the etheno adducts are implicated as initiating DNA damage in copper/iron-induced carcinogenesis in humans and should also be explored as biomarkers in disease progression and prevention trials.