In rats, lesions of the cerebellar fastigial nucleus, but not lateral nuclear lesions or cerebellar cortical lesions, resulted in significant reductions in activity, open-field exploratory behavior, and social interactions. These deficits showed no recovery over a 4-wk testing period and were not related to the motor effects of the lesions. Other motivated behaviors, such as eating, grooming, gnawing, and pain responsiveness, were minimally affected. This pattern of results, together with other findings, suggests the existence of two separate fastigial output pathways to neurobehavioral substrates. One of these is the direct fastigio-bulbar pathway, which mediates the eating, grooming, and gnawing behaviors elicited by fastigial stimulation. The other is the ascending fastigial projection to limbic structures, which may mediate fastigial influences on activity and social interaction.