Benzene, toluene and xylenes (BTX) are aromatic hydrocarbons widely used as industrial chemicals. Due to their formation in many combustion processes, they are widespread environmental pollutants. Thus, the general population undergoes lifelong exposure to these pollutants, and some categories of workers are exposed at particularly high levels. In order to evaluate human exposure to BTX, mercapturic acids (MA) have recently been proposed as the most specific biomarkers, but only S-phenyl mercapturic acid (S-PMA) has been validated as a biomarker for benzene. Furthermore, S-benzyl mercapturic acid (S-BMA) and S-benzyl methyl mercapturic acid (S-BMMA), metabolites of toluene and o-xylene, respectively, have been less extensively investigated. In this paper, we evaluated exposure to BTX in a group of 354 traffic wardens by measuring the urinary concentration of S-PMA, S-BMA and S-BMMA using a method based on liquid-chromatography-tandem mass spectrometry. This analytical method was fully validated according to U.S. Food and Drug Administration guidance. All samples showed a measurable concentration of S-BMA (mean: 12.84 microg/g (creatinine)), while S-PMA and S-BMMA resulted quantifiable only in about 30% of the analyzed urines (mean: 1.76 and 3.98 microg/g(creatinine), respectively).