Phencyclidine (PCP) is a drug that has been widely abused in the past two decades. PCP produces place aversion, but not preference, in the place conditioning test. The present study examined PCP-induced place conditioning behavior in rats treated with PCP repeatedly. In naive rats, PCP (2-8 mg/kg i.p.) dose dependently produced place aversion, but did not produce any effect in rats treated with PCP (10 mg/kg i.p.) for 14 days. indicating that tolerance developed to PCP-induced place aversion on repeated PCP treatment. In rats treated with PCP (10 mg/kg i.p.) for 28 days, PCP (2-8 mg/kg i.p.) dose dependently produced place preference. These findings suggest that some changes in neuronal function induced by the repeated PCP treatment may play an important role in the addiction to this drug.