Abstract Background and objective: An important issue in human biomonitoring is determining how exposure duration affects the kinetics of molecular biomarkers. In this study we compare the influence of exposure variables on DNA adducts. Methods: DNA adducts were analysed by 32P-postlabelling in lympho/monocytes of 677 Caucasian subjects. Results: After correction for other variables, DNA adducts increased depending on the length of occupational and smoke exposures. Higher DNA adducts were detected in workers with more than 14 years of exposure than in workers with shorter exposures (RR = 1.19, p = 0.049) and in smokers with more than 10 years of exposure than in smokers with shorter exposure (RR = 1.21, p