Effects of carbamazepine on behavioral sensitization to morphine in mice has been investigated. Mice treated daily for 7 days with morphine (10 mg/kg) induced behavioral sensitization. Carbamazepine (10, 20, 40 mg/kg, i.p.) itself dose-dependently inhibited the locomotor activity of mice, but did not affect the acute morphine induced hyperactivity. Chronic treatment with carbamazepine had no effect on the development of morphine behavioral sensitization. Co-administration of carbamazepine 30 min prior to morphine had no significant effect on the development of behavioral sensitization. After the behavioral sensitization has been established, carbamazepine (10, 20, 40mg/kg, i.p.) did not affect the expression of morphine sensitization. However, carbamazepine (10, 20, 40mg/kg, i.p.) dose-dependently potentiated the transfer of morphine sensitization. The data of the present study implies that carbamazepine may influence the maintenance process of behavioral sensitization, which results in the enhancement of the transfer of behavioral sensitization. In clinic, the present results suggest that chronic use of carbamazepine might have abuse potential in opioid abusers.