Striatal spiny neurones serve as a major anatomical locus for the relay of cortical information flow through the basal ganglia. these projection neurones also represent the main synaptic target of cholinergic interneurones, whose physiological role in striatal activity still remains largely enigmatic. The striatal cholinergic system has been implicated in the pathophysiology of movement disorders such as Parkinson's disease, but the cellular mechanisms underlying cholinergic-neurone function are still unknown. On the basis of in vitro electrophysiological evidence, obtained from a rat corticostriatal-slice preparation, we propose that endogenous ACh exerts a complex modulation of striatal synaptic transmission, which produces both short-term and long-term effects. ACh-mediated mechanisms might be of crucial importance in processing the cortical inputs to the striatum.