Six-week-old male albino hairless mice (Hos: Hr-1) were exposed to a near-ultraviolet (UV) fluorescent sun lamp (33.5 kJ/m2/hr; wave length > 270 nm with a peak at 312.5 nm) to investigate the induction of oxidative DNA damage in epidermal cells. Significantly higher levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) were detected in a dose-dependent manner in epidermis of mice exposed to near-UV than in those of control animals. The ratio of 8-OHdG in near-UV-exposed/unexposed control was 2.08 +/- 0.19 after 168 kJ/m2 exposure, P < 0.01; 3.49 +/- 0.36 after 335 kJ/m2 exposure, P < 0.01 (means +/- SE). The levels of 8-OHdG decreased with time after near-UV exposure, suggesting the presence of removal and/or repair mechanisms. This is the first report that oxidative DNA base modification is induced in vivo in epidermal cells by near-UV exposure. Oxidative DNA base modification may be one of the causes of sunlight-induced skin carcinogenesis.