Chlorinated solvents are defined as carcinogenic substances by the International Agency for Research on Cancer (IARC). Trichlorethylene, tetrachloroethylene and 1,1,1-trichloroethylene undergo biological transformation by cytochrome P-450 monooxygenase or to produce trichloroethanol (TCE) and trichloroacetic acid (TCA) by alcohol dehydrogenase and aldehyde dehydrogenase. Trichlorethylene and tetrachlorethylene are widely used, especially as metal degreasers, in the dry-cleaning industry, and in the manufacture of various products such as adhesives and paint removers. In order to evaluate workers' exposure to chemicals, it is necessary to evaluate urine levels of not only the main component but also its metabolites, TCA and TCE, which have a relatively longer biological half-life.