Until now, high-performance liquid chromatography (HPLC) and gas chromatography (GC) have been shown the most useful techniques for the determination of urinary mercapturic acids in humans. Preliminary sample treatment is often necessary, including liquid-liquid, solid phase (SPE) or on-line extraction, in order to obtain highly purified samples. The use of derivatizing reagents coupled with specific and sensitive detectors allowed to develop methods suitable for the measurement of mercapturic acids specific for a large number of xenobiotics. At present, however, the use of urinary mercapturic acid tests for biomonitoring purposes is limited because of the high costs and complexity of analyses. Further improvements, in terms of cost reduction, could come from the introduction of fully automated systems.