Xylene is the most widely used solvent only second to toluene. In practical application, 3 xylene isomers are present together with toluene and ethylbenzene especially when technical grade xylenes are in use. Toluene and 3 isomers of xylenes are metabolized primarily to hippuric acid (HA) and corresponding isomers of methylhippuric acids (MHA), respectively, whereas ethylbenzene is biotransformed to phenylglyoxylic acid (PhGA) and mandelic acid (MA), so simultaneous determination of the 6 metabolites is requested for comprehensive biological monitoring of exposure to the solvent mixture by means of urinalysis. In the present study, a simple high-performance liquid chromatographic (HPLC) procedure is described as a method for simultaneous determination of the 6 metabolites in urine; urine analysis was selected in the present study because of its non-invasive nature in sampling with minimal burden on exposed workers.