DNA polymerase lambda, pol lambda, is a eukaryotic member of the X-family DNA polymerases that is involved in two modes of DNA repair, i.e. base excision repair (BER) or non-homologous end joining (NHEJ). Using immunohistochemical approaches, we have observed pol lambda expression in human tissues, particularly in the respiratory system of lung cancer patients. pol lambda proteins were distributed in the nuclei of the epithelial cells in the bronchi, bronchioles and alveoli. Intriguingly, the level of pol lambda expression in the bronchiolar epithelia significantly correlated with the amount of habitual smoking in the individuals. Conversely, pol lambda expression in cancer tissues did not correlate with the smoking status of the patients. Pol lambda expression was sometimes discrepant between the tumor tissues and adjacent bronchioles. More importantly, tumors without pol lambda expression that occurred in heavy smokers significantly tended to be at an advanced clinical stage. Pol lambda may thus be involved in the DNA repair processes counteracting DNA damage caused by tobacco smoke in the respiratory system.