Urinary metabolites of styrene, i.e., mandelic acid, phenylglyoxylic acid and hippuric acid, were determined by high performance liquid chromato-graphy. Female Wistar rats were administered various amounts of styrene intraperitoneally, and the metabolites in the urine were determined at suitable intervals after the injection. The amounts of urinary mandelic and phenyl-glyoxylic acids were in proportion to the amount of administered styrene. The amount of urinary metabolites per body weight per hour reached a maximum level in the urine from the 10-24 hr period. In another experiment, tetrachlo-romethane was injected intramuscularly into rats prior to the administration of styrene. The amounts of urinary mandelic, phenylglyoxylic and hippuric acids in the tetrachloromethane-administered group were much less than those of the control group.