After two volunteers were exposed to 65.0 ppm ethylbenzene for 3 hours, the metabolites of ethylbenzene in their urine, mandelic acid(MA), hippuric acid(HA) and phenylglyoxylic acid(PhGA) were analyzed. The metabolites were excreted in the urine in the order of MA>HA>PhGA. The highest value of excretion of metabolites was observed six to ten hours after the beginning of exposure. MA/PhGA and HA/PhGA mole ratios of total excretion in urine were 3.5 and 2.6, respectively.