Intraperitoneal administration of MK-801 (0.1 mg/ kg), an N-methyl-D-aspartate (NMDA) receptor antagonist, before and during methamphetamine treatment inhibited methamphetamine-induced conditioned place preference (CPP) in mice. Behavioral sensitization to a dopamine (DA) receptor agonist apomorphine that developed in methamphetamine-induced CPP mice was also inhibited by MK-801. Furthermore, MK-801 inhibited apomorphine-induced postsynaptic dopaminergic action, cage-climbing behavior. Therefore, the present studies suggest that methamphetamine-induced behaviors, such as CPP and behavioral sensitization, may be closely related to the dopaminergic activation mediated via the NMDA receptor. The behavioral sensitization to apomorphine may be a possible underlying mechanism of methamphetamine-induced CPP, because behavioral sensitization developed in methamphetamine-induced CPP mice, as well as apomorphine-induced climbing behavior in mice, were inhibited by MK-801.