A gas chromatographic method for simultaneous determination of hippuric and o-, m-, and p-methylhippuric acids (metabolites of toluene and xylene) in urine is described. The analytical procedure is based on the extraction of the aromatic metabolites with ethyl acetate containing the internal standard and on a methylation with 3-methyl-1-p-tolyltriazene. With this method, which does not require much time and handling, the different acids can be satisfactorily determined with high sensitivity and specificity. A statistical study shows a good reproducibility for the determination of hippuric and o-, m-, and p-methylhippuric acids. The coefficient of variation for 10 determinations in all cases was less than 5%.