Abstract:Objective :To study the effect of naloxone on the acquisition and retention of conditioned place aversion (CPA) in morphine treated rats .Methods :Rats were made physically dependent on morphine with the initiative dose (6or 12mg/kg)by intraperitoneal injection in 2 0 % increasedevery day within 10days,and were trained to develop CPA induced by naloxone (0 .5or 1.0mg/kg)ina biasedthree chamberconditionedplaceapparatus .Results :Naloxone produced distinct CPA in the morphine dependentrats .Nodose responserelationshiphas been found for morphine and naloxone in our experiment on the acquisition and retention of CPA in dependent rats .The conditioning training with naloxone produced CPA in the dependent rats ,however ,that with naloxone in the abstinent rats did not.Conclusions :Naloxone could play different roles in the acqusition of CPA at thephase of mor phine treated orabstinence in rats .