The determination of chlorinated phenols in urine can be used as a means for assessing exposure to pesticides and industrial chemicals in the human population. A method was developed for the analysis of chlorinated phenols which involves the derivatization of metabolites from the urine of rats fed hexachlorobenzene (HCB) and pentachlorophenol (PCP). This method was then applied to urine samples taken from the general human population to gain a background level. Pentachlorophenol was detected in greater than 90% of the human samples analyzed. The only other metabolites detected were tetrachloropyrocatechol and tetrachlorohydroquinone along with large amounts (greater than 3 ppm) of PCP. Pentachlorothiophenol, a major metabolite of HCB fed to rats, was not detected in human urine. The analysis of human urine for underivatized chlorinated phenols using a direct gas chromatographic method not requiring derivatization detected quantifiable levels of 2,5-dichloro-2,5-dichloro-2,4,5-trichloro-,2,3,4,6-tetrachloro- and pentachloro-phenolis greater than 90% of the samples examined. Approximately 50% of the samples, contained detectable levels of 2,6 and 3,5-dichlorophenol and 2,4,6-trichlorophenol.