Single-unit recordings from neostriatal neurons showing movement-related excitations were obtained in freely moving, cortically ablated rats and sham-lesioned controls. d-Amphetamine (AMPH, 1.0 mg/kg s.c.) increased neuronal activity relative to resting baseline firing rates in both groups of animals, but cortical ablation significantly attenuated this effect. A behavioral clamping analysis, which compared neuronal activity during identically rated pre- and post-AMPH behaviors, revealed that: (a) AMPH enhanced movement-related neuronal activity in sham-lesioned controls, but not in cortically ablated rats; and (b) the drug-induced neuronal activation in control rats was not simply secondary to the behavioral activation produced by AMPH. In contrast to its neuronal effects, cortical ablation did not affect ratings of AMPH-induced locomotion, rearing, or head movements, though sniffing scores showed a postive correlation with lesion size. Thus, corticostriatal projections are critically involved in AMPH-induced excitations of neostriatal motor-related neurons.