The authors have developed a dynamic headspace (purge-and-trap) gas chromatographic method, with photoionization detection, for the determination of benzene (C6H6), toluene (C7H8), ethylbenzene (C8H10), and isomeric (o-, m-, p-) xylenes (C8H10) (BTEX) in urine. Detection limits ranged between 15 and 35 ng/l, relative standard deviations between 0.2 and 10%, and accuracy between 80 and 100%. The primary objective of this study was to use this new method to establish baseline concentration data for BTEX in the urine of the general population of Zagreb, Croatia. A second objective was to evaluate the effect of cigarette smoking on those baseline values. BTEX were analyzed in the urine of 72 subjects (36 nonsmokers and 36 smokers) without occupational exposure to BTEX. The nonsmokers had measurable BTEX in their urine, except for ethylbenzene in 13 and o-xylene in 15 of the samples. Values for BTEX were markedly higher among smokers than nonsmokers. Because the sources of BTEX exposure are commonly derived (i.e., vehicle exhausts and smoking), their values in subjects' urine were significantly intercorrelated. Levels of toluene and o-xylene were correlated significantly with the number of cigarettes smoked per day. The use of purge-and-trap gas chromatography with photoionization detection to determine BTEX in urine offers a convenient approach for biological monitoring of the general population. Study data provide referent values for BTEX in urine, which can be used as biomarkers for environmental exposures. Smoking contributes significantly to the urinary concentration of BTEX.