Blood samples were obtained from 61 volunteers working in a Finnish iron foundry who were exposed to carcinogenic polycyclic aromatic hydrocarbons and from 19 control subjects not known to be exposed to these chemicals. Foundry workers were categorized into high, medium, or low exposure groups, based on their exposure levels to airborne benzo[a]pyrene (BaP) (high greater than 0.2, medium 0.05-0.2, low less than 0.05 micrograms BaP/m3 air). Aromatic adducts were determined in white blood cell DNA from exposed and unexposed subjects using 32P-postlabeling. There was a highly significant correlation between the estimated exposure and adduct levels as determined by analysis of variance. The levels of adducts found in the high and medium group samples ranged from 5 to over 20 adducts in 10(8) DNA nucleotides. No effects due to age, sex, or the smoking habits of the subjects were observed. Within each group, the SEM appeared rather small. This study demonstrates the utility of the 32P-postlabeling assay to assess human exposure to known and unknown environmental aromatic genotoxicants.