The role of the N-methyl-D-aspartate (NMDA) and non-NMDA excitatory amino acid (EAA) receptors in the mechanism of behavioral sensitization to amphetamine-induced sterotypy was investigated in mice. The results confirm previous observations that NMDA antagonists can block the induction of the phenomenon but not the expression; in contrast, DNQX, a non-NMDA receptor antagonist, can block both the induction and the expression of the sensitization. The differential effects of the two classes of antagonists suggest that the induction and the expression are the result of different mechanisms, both of which involve the EAA system. The DNQX results differ from those of haloperidol, which can also block both the induction and expression, because haloperidol can completely block the amphetamine-induced responses in naive and in sensitized animals; whereas DNQX is without effect on the amphetamine activity in naive animals and, in the sensitized animal, can block only that portion of the response that is derived from the sensitization phenomenon. The effects of the EAA antagonists support the hypothesis that the enhanced responsiveness in the sensitized animals is derived from the activation of EAA receptors, which, in turn, increases the release of dopamine in the striatum. Finally, the involvement of the non-NMDA receptors in the expression of the behavioral sensitization further substantiates the postulate that the amphetamine-induced sensitization is a behavioral manifestation of long-term potentiation (LTP).