Methods were developed for the determination of urinary phenylmercapturic acid (PMA), a metabolite specific for benzene, benzylmercapturic acid (BMA), a metabolite of toluene and phenylhydroxyethylmercapturic acids (PHEMAs), specific for styrene, in human beings. Methods involved sample clean up followed by deacetylation and derivatization of the compounds with o-phthaldialdehyde and 2-mercaptoethanol. The fluorescent derivatives were separated on reversed-phase columns with gradient runs and detected by a fluorescence detector. The detection limits were 0.5 microgram/l for PMA and BMA, and 7 micrograms/l for PHEMAs. The background levels of PMA were higher in smokers than in nonsmokers, while no difference was found in the levels of BMA and PHEMAs. Coexposure to ethanol enanched the excretion of BMA in subjects experimentally exposed to toluene. Correlations were found between environmental benzene (r = 0.74, log transformed data), toluene (r = 0.74) or styrene (r = 0.56) and specific mercapturic acids in workers. The usefulness of PMA, BMA and PHEMAs as biomarkers is critically evaluated.