Benzene is classified by IARC as a human carcinogenic compound. Benzene is present in mainstream, side stream and environmental tobacco smoke. Various methods for the biological monitoring of exposure of smokers and nonsmokers to benzene are available. The methods are based either on the direct determination of benzene in exhalate, blood and urine or on the analysis of metabolites (phenol and other phenolic derivatives, trans,trans-muconic acid, and S-phenylmercapturic acid (S-PMA)) in urine. Among the metabolites S-PMA (although a relatively minor product) is considered the most specific, and is therefore particularly suitable for assessment of benzene exposure. Depending on available technology, different methods for the determination of S-PMA have been developed in our laboratory since the early nineties. In 1990 the first procedure utilized high resolution gas chromatography (HRGC) with flame photometric detection. The limit of determination (LOD) was 50 µg/l urine. With the introduction of HRGC with mass spectrometric detection (in 1994) a LOD of 0.1 µg/l - which is necessary for the determination of S-PMA in the urine of low exposed persons - could be reached. But both methods suffer from their time-consuming clean up. Recently we have developed a method using high-performance liquid chromatography (HPLC) with tandem mass spectrometry (Micromass Quattro Micro). This method is quick and sensitive (LOD = 0.1 µg/l). In the presentation the advantage of HPLC with tandem mass spectrometry for metabolite analysis in general and for the determination of S-PMA in particular will be demonstrated.