Cigarette smoking generates an oxidative stress in the lung, which may contribute to the pathogenesis of chronic obstructive pulmonary disease. We performed an immunohistochemical study to evaluate oxidative stress in the lung after acute cigarette smoke (CS) exposure in mice. Paraffin-embedded lung tissue sections were prepared from mice exposed and unexposed to CS for 1 h. The sections were immunostained with antibodies against 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidative DNA adduct, and 4-hydroxy-2-nonenal (4-HNE), a lipid peroxidation product. The bronchiolar and alveolar epithelium of mice unexposed to CS exhibited weak signals for 8-OHdG and 4-HNE, whereas by 1 h after CS exposure the signals in the bronchiolar epithelial cells and the alveolar epithelial cells, particularly type II cells, had increased dramatically. The increases in both were associated with increased 8-OHdG levels in bronchoalveolar lavage fluid as determined by enzyme-linked immunoassay. These results suggest that acute CS exposure imposes oxidative stress predominantly on bronchiolar epithelial and alveolar type II cells, confirming that cigarette smoking causes oxidative damage to the respiratory epithelium.