An immunoperoxidase method using a polyclonal antiserum which recognizes benzo(a)pyrene and structurally related polycyclic aromatic hydrocarbon diol epoxide-DNA adducts has been developed for the detection and quantitation of DNA damage in single cells. The method was used initially on 10T1/2 cells treated with [3H]anti-benzo(a)pyrene diol epoxide then applied to the detection of adducts in oral mucosa cells of smokers and nonsmokers. Levels of DNA damage were elevated in each of 16 smokers (mean relative staining, 503 +/- 104) compared to 16 age-, race- and sex-matched nonsmokers (251 +/- 82; P < 0.0001). There was an approximately 3-fold range in relative staining in both smokers (252 +/- 125 to 663 +/- 189) and nonsmokers (157 +/- 72 to 431 +/- 269) suggesting the importance of individual differences in capacity to metabolize the carcinogens and/or repair damaged DNA. This noninvasive method, requiring small numbers of cells, will be useful for routine monitoring of DNA damage in intervention studies as well as for biofeedback in smoking cessation programs.