The neuropeptide bombesin was administered centrally to conscious, unrestrained rats. Bombesin caused a dose-dependent increase in locomotor behavior, as well as licking and grooming. The effect on locomotion was most readily elicited when bombesin was infused into the nucleus accumbens, and was attenuated by pretreatment with haloperidol but not atropine or diphenhydramine. Centrally administered bombesin did not change regional levels of dopamine or its principal metabolites.