This work studied the interactions between cholinergic and adenosine systems in the denervated striatum. For that purpose, we evaluated the effects of an intrastriatal administration of the muscarincic receptor agonist, oxotremorine-M on turning behavior induced by systemic caffeine in unilaterally 6-hydroxydopamine-lesioned rats. Low doses of oxotremorine-M (0.1 ng/microl) enhanced, whereas high doses (100 ng/microl) attenuated contralateral turning induced by caffeine. These results support a functional link between muscarinic and adenosinergic systems in the denervated striatum and suggest opposite actions of muscarinic M2 and M1 receptors on caffeine-induced turning behavior.