To clarify the effect of toluene on behavior, and to evaluate urinary orthocresol excretion as an indicator of toluene exposure and locomotor activity, we have investigated the urinary orthocresol excretion and levels of locomotor activity in rats exposed to 0-3000 ppm of toluene intermittently for 2 hours. The levels of locomotor activity were measured by a laboratory animal activity measuring apparatus (ANIMEX-III). Exposure of adult male rats to more than 1000 ppm (v/v) of toluene caused an elevation of the urinary orthocresol excretion and a good correlation was noted between the amount of toluene in the air and the urinary orthocresol excretion. Exposure to over 2000 ppm of toluene suppressed the level of locomotor activity, and there was a good correlation between the level of locomotor activity and the urinary orthocresol excretion. Further, rats exposed to 3000 ppm toluene showed elevated levels of locomotor activity during a 10-hour period after exposure. These patterns of urinary orthocresol excretion and the levels of locomotor activity remained unchanged even when rats were exposed to 3000 ppm of toluene intermittently over a 4-day period.