1. Peptides such as cholecystokinin have been reported to modulate the effects of dopaminergic agonists on locomotion in rats. 2. The present experiments tested the possibility that lithium interacts with dopaminergic function through the same mechanism by which cholecystokinin potentiates dopaminergic function. 3. The results suggest that dietary lithium has no effect on the ability of either dopamine alone, or the combination of dopamine plus cholecystokinin, microinjected directly into the nucleus accumbens, to stimulate hyperlocomotion.