A comparative evaluation of urinary biomarkers was carried out to characterize benzene exposure in a group of 100 traffic policemen of the city of Parma (Italy). All subjects were monitored once, in two consecutive days characterized by similar climatic conditions but preceded by two windy days. Benzene ambient concentration measured by municipal air monitoring stations was 1 microg/m(3) (Day 1) and 2 microg/m3 (Day 2). Personal exposure to ambient concentrations of benzene, toluene, ethylbenzene and xylene (BTEX) was assessed by using Radiello((R)) passive-diffusive samplers in a subgroup of 24 workers. Benzene metabolites, t,t-muconic acid (t,t-MA) and S-phenylmercapturic acid (S-PMA) were determined by isotopic dilution liquid chromatography-tandem mass spectrometry on spot urine samples collected at the end of the shift. Urinary benzene (U-B) was determined by solid-phase microextraction gas chromatography-mass spectrometry. Airborne benzene concentration expressed as median [and interquartile range] was 6.07 [0.28-9.53] microg/m(3), as assessed by personal sampling. Urinary concentrations of biomarkers in the whole group were 41.8 [34.1-89.8] microg/g creatinine for t,t-MA, 0.67 [0.23-1.32] microg/g creatinine for S-PMA, and 0.16 [0.13-0.26] microg/l for U-B. Smokers eliminated significantly higher concentrations of unchanged BTEX and benzene metabolites than non-smokers (p < 0.05). When traffic policemen were distinguished into indoor (n=31) and outdoor workers, no significant differences were observed for either airborne benzene or urinary biomarkers. Significantly lower concentrations of S-PMA and U-B were determined in samples collected at Day 1 as compared to Day 2 (p < 0.0001 and p = 0.003, respectively) suggesting that these biomarkers are enough sensitive and specific to detect changes in airborne benzene concentration even at few microg/m(3).