The metabolism of toluene and m-xylene, which were injected into rats, was studied. A linear relationship existed between the amount of toluene injected into rats and urinary HA in the range of over 0 to 2.05 mmoles/kg of toluene. The same relationship was noted with m-xylene. Amounts of HA and m-MHA excreted in urine decreaed with the lapse of time from the 1st to 3rd day. The amounts recovered to the level before the injection on the 3rd day.