The 8-hydroxydeoxyguanosine (8-OH-dG) levels in the peripheral parts of human lung tissues were compared between lung cancer patients (n=70) and non-cancer patient controls (n=15). An increased level of 8-OH-dG was observed in the lung cancer group, in both the adenocarcinoma and non-adenocarcinoma (mainly squamous cell carcinoma) groups, as compared to the non-cancer control group. This result suggests that reactive oxygen species are partly involved in the induction of lung carcinomas (both adenocarcinoma and non-adenocarcinoma).