It has been hypothesized that mutational events may be involved in the atherogenetic process and that at least a portion of atherosclerotic plaques may develop according to an initiation-promotion process of arterial smooth muscle cells, akin to benign tumors. We conducted a study to evaluate the occurrence of oxidative DNA damage and formation of DNA adducts in human atherosclerotic lesions and to assess the relationships of these promutagenic alterations with exposure to atherogenic risk factors. Pure DNA was extracted from the tunica media (composed mainly of smooth muscle cells) of abdominal aorta fragments taken at surgery from 85 patients suffering from severe atherosclerotic lesions. DNA adducts were detected by synchronous fluorescence spectrophotometry and 32P postlabeling after enrichment of adducts with either butanol or nuclease P1. 8-Hydroxy-2'-deoxyguanosine (8-OH-dG), a typical indicator of oxidative DNA damage, was measured by HPLC/electrochemical detection. A complete questionnaire reporting general, clinical, and laboratory characteristics was available for each patient. All 84 samples tested by 32P postlabeling were positive by displaying the presence of diagonal radioactive zones and up to 9 individual DNA adducts. Of 52 samples tested, 32 (61.5%) yielded typical positive signals at synchronous fluorescence spectrophotometry. All but one of 39 samples tested had very high levels of 8-OH-dG, thus showing a remarkable oxidative DNA damage. Statistically significant correlations were found between the levels of molecular biomarkers and atherogenic risk factors including age, number of currently smoked cigarettes, ratio of total-to-high density lipoprotein blood cholesterol, blood triglycerides, and blood pressure. The DNA alterations detected in our study may be only one component of the genetic basis of atherogenesis. Moreover, no causal role in the atherogenetic process can be inferred from our results. However, DNA alterations, including oxidative damage and adduction of reactive molecules of either endogenous or exogenous source, were systematically present in the smooth muscle cells of human atherosclerotic lesions and their intensity was significantly correlated with the occurrence of atherogenic risk factors in the patients studied.