Abstract To evaluate the possible contribution of dorsal striatal glutamate receptors to motor behavior, circling responses were observed in rats following unilateral intrastriatal microinjections of the agonist, N- methyl- d- aspartate (NMDA) or the antaagonist, 2-amino-7-phosphonoheptanoic acid (APH). The role of dopamine (DA) in NMDA-produced circling also was evaluated. In experiment 1, an NMDA dose of 5.0 μg (in 0.5 μl), but not 0.5 or 0.05 μg produced significant contraversive circling. In experiment 2, an APH dose of 10.0 μg but not 1.0 or 0.1 μg produced significant ipsiversive circling. In experiment 3, microinjection of the ineffective 0.1 μg dose of APH or a dose (20 μg) of the DA antagonist, cis-flupenthixol, that did not produce circling when administered alone, significantly reduced the circling response produced by the 5.0 μg dose of NMDA. As NMDA produced circling in the same direction as that seen following similar unilateral injections of locomotion-stimulating DA agonists, the present results suggest that glutamate, acting via NMDA receptors in the dorsal striatum, may exert an excitatory influence on motor systems. The observation that a DA receptor blocker antagonized the NMDA response further suggests that the observed motor excitatory effect of glutamate at NMDA receptors requires concurrent stimulation of DA receptors in the same region of the striatum.