Male Wistar rats were exposed to ethylbenzene (0, 300, or 600 ppm for 6 h), and the metabolic fate of the compound was elucidated on the basis of the biotransformation products found in the urine. Fourteen different compounds thought to originate from ethylbenzene were identified. The main metabolites were 1-phenylethanol, mandelic acid, and benzoic acid. The metabolic conversion proceeded mainly through oxidation of the side chain, whereas ring oxidation seemed to be of minor importance. At the exposure level of 600 ppm, only 6% of the amount absorbed was eliminated in the urine during exposure. During the period of 48 h from the onset of exposure, the total urinary elimination was 59%. The corresponding values at 300 ppm were 13 and 83%.