The purpose of this study was to determine whether or not chronic exercise could cause long-term metabolic plasticity in cerebellum. The activity of cytochrome oxidase (COX), coupled to ATP production, reflects long-term plasticity in metabolic capacity. The present study examined whether or not 10 weeks of voluntary exercise would increase COX activity in the cerebellum. Adult male Sprague-Dawley rats were randomly assigned to a control or exercise condition. Exercising rats had running wheels attached to their home cages. COX activity was measured using histochemical methods and optical densitometry. Rats in the exercise condition had significantly higher optical density in spinocerebellum (mainly in lobules 3, 4, 5, 8, 9 and in the copula), but not in neocerebellar crura I and II.