To evaluate the effect of cigarette smoking on oxidative stress in lung tissues, we compared the levels of a type of oxidative DNA damage, 8-hydroxydeoxyguanosine (8-OH-dG), in tissue obtained from the central sites of lungs from 14 current smokers, seven ex-smokers and nine non-smokers. The mean level of 8-OH-dG in the lung tissues from smokers was 1.43-fold higher than that of the non-smokers (the difference was statistically significant, P = 0.0262). A positive correlation between the 8-OH-dG levels in normal lung tissues and the Brinkman index was obtained from smokers and ex-smokers (r = 0.525; P = 0.0134). A positive correlation was also obtained for the 8-OH-dG levels in normal lung tissues and the number of cigarettes smoked per day (r = 0.436; P = 0.0132). These results suggest that oxidative DNA damage is induced in lung DNA by cigarette smoking.