The present study was designed to investigate the effect of cholinergic stimulation of the nucleus accumbens (NA) on locomotor behavior. Microinjection of the cholinergic agonist, carbachol, into the NA resulted in a dose-dependent increase in spontaneous locomotor activity. Pretreating rats with the nicotinic antagonist, mecamylamine, significantly reduced the carbachol-induced locomotor response, whereas pretreatment with the muscarinic antagonist, atropine, was ineffective. Injection of the dopamine antagonist, haloperidol, prior to stimulation of the NA with carbachol, significantly attenuated the motor stimulant effect of carbachol. Evidence has accumulated to suggest that the increased locomotor response elicited from NA stimulation is mediated by GABAergic efferents from the NA to the substantia innominata (SI). Pretreatment with the GABA agonist, muscimol, into the SI significantly antagonized the locomotor hyperactivity induced by carbachol injection into the NA. Taken together, these data indicate that carbachol produces a motor stimulant effect by activating nicotinic receptors which may modulate the release of dopamine in the NA and inhibit the GABAergic efferents to the SI.