Male and female rats of the Fischer Strain were dosed with 550 mg/kg of benzene or corn oil vehicle on Days 9, 11 and 13 postpartum. The spontaneous motor activity of benzene exposed rats (males and females) was found to be elevated when tested at 100-130 days of age. When challenged with various doses of d-amphetamine (0.3-3 mg/kg), the benzene exposed rats were found to be less sensitive to the motor activity increasing effects of the drug. In a subsequent test to measure specific components of exploratory activity in an operant chamber (nose-poking, wall rearing, lever touching), female rats exposed to benzene were found to emit fewer rearing responses. Body weights and performance in a battery of tests to assess neurobehavioral toxicity (Days 45, 60 and 100 postpartum) were not affected by postnatal exposure to benzene. These data indicate that postnatal exposure to benzene can produce significant alterations in the motor activity of rats when tested during adulthood and the type of effect depended on the procedure used. Changes in the sensitivity of benzene exposed animals to d-amphetamine suggest long-term alterations in catecholaminergic function.