In our research project entitled "Chemical irritative and/or genotoxic effect of fumes of bitumen under high processing temperatures on the airways," 73 mastic asphalt workers exposed to fumes of bitumen and 49 construction nonexposed workers were analyzed and compared with respect to polycyclic aromatic hydrocarbons (PAHs) exposure and exposure-related health effects. In order to assess the internal exposure the monohydroxylated metabolites of pyrene, 1- hydroxypyrene (1-OHP), and phenanthrene, 1-, 2- and 9-, and 3- and 4-hydroxyphenanthrene (OHPH) were determined in pre- and post-shift urinary samples. Significantly higher concentrations 1-OHP and OHPH were detected in the post-shift urine samples of 7 mastic asphalt workers working on the same construction site compared to the reference workers and all other 66 mastic asphalt workers. The adjusted mean OHPH in the reference, 66 mastic worker, and 7 worker subgroups was 1022, 1544, and 12919 ng/g creatinine (crn) respectively, indicating a marked rise in the 7 worker subgroup. In addition, there was a more than 12-fold increase of PAH metabolites from pre- to post-shift in these 7 workers, whereas in the other mastic asphalt workers there was only a twofold rise in PAH-metabolite concentration between pre- and post-shift values. The analysis of a drilling core from the construction site of the seven workers led to the detection of the source for this marked PAH exposure during the working shift as being coal tar plates, which were, without knowledge of the workers and coordinators, the underground material of the mastic asphalt layer. The evaluation of the stationary workplace concentration showed enhanced levels of phenanthrene, pyrene, fluorene, anthracene, and acenaphthene during working shifts at the construction site of these seven workers. Our study shows that biological monitoring is also a useful tool for the detection of unrecognized sources with high PAH concentrations.