The release of striatal cholecystokinin, glutamate, aspartate and dopamine was studied in vivo with microdialysis in decorticated rats, with or without callosotomy. Unlesioned rats were also analysed. Unilateral decortication produced a unilateral decrease in K(+)-stimulated extracellular striatal glutamate and aspartate levels, without decreasing cholecystokinin or dopamine levels. However, following decortication plus callosotomy, basal and K(+)-stimulated extracellular cholecystokinin and glutamate levels were significantly decreased in the striatum ipsilateral to side of decortication. Aspartate levels were bilaterally decreased. These results give evidence for the existence of crossed corticostriatal projections containing releasable cholecystokinin and glutamate.