The quantitative analysis of 8-hydroxy-2'-deoxyguanosine (oh8dG) in human peripheral blood cells was carried out to find integrated biomarkers for estimating cancer risk. The change of the oh8dG levels over time in two healthy volunteers was measured to evaluate a intraindividual variance and each individual value was confirmed to be almost constant when they maintained usual life style. We applied this measurement to asbestosis patients who had worked in dockyard for 19-42 years. The oh8dG were detected in all samples and ranged from 0.77 to 1.28/10(5) deoxyguanosine (dG)8. No significant differences was observed in mean values of oh8dG between patients (1.00 +/- 0.17/10(5)dG) and hospital control group without asbestos exposure (1.03 +/- 0.20/10(5)dG) No association was found with the status of cigarette smoking. The oh8dG level in peripheral blood cells is therefore not a sensitive biomarker for past asbestos exposure at low levels.