Repeated administration of cocaine led to increases in ambulation-accelerating activity (sensitization) and conditioned place preference (CPP). Dopamine (DA)-receptor supersensitivity was also developed in cocaine-induced sensitized and CPP mice. An N-methyl-D-aspartate (NMDA)-receptor antagonist, MK-801, blocked simultaneously developments of cocaine-induced behavioral sensitization, CPP, and DA-receptor supersensitivity. Furthermore, MK-801 inhibited a apomorphine-induced striatal dopaminergic action: climbing behavior. These results suggest that the cocaine-induced dopaminergic behaviors such as sensitization to ambulatory activity and CPP may be produced via activation of the NMDA receptor. The development of postsynaptic DA-receptor supersensitivity may be an underlying common mechanism that mediates cocaine-induced behavioral sensitization and CPP.