Lung tissues from 32 cases of lung cancer with surgical operation, 22 smokers and 10 nonsmokers, were analyzed with P1-mediated modification of 32P-postlabelling technique. The level of lung DNA-adduct in cigarette smokers was higher that in nonsmokers with significant difference (P < 0.001). Autoradiogram showed a diagonal radioactive zone in smokers' lung tissues. Correlation analysis indicated DNA-adduct in lung tissues increased with the number of cigarettes smoked with a regression equation of Y = 0.411 X + 3.52, r = 0.74, P < 0.001.