The effects of unilateral stimulation of the cerebral motor cortex and of the visual cortical area on the activity of the nigrostriatal dopaminergic neurons were examined in halothane-anesthetized cats. For this purpose, one push-pull cannula was inserted in each caudate nuclei and another one in the substantia nigra ipsilateral to the stimulated side. In all cases, the release of [3H]dopamine ([3H]DA) continuously formed from L-[3,5-3H]tyrosine was estimated in superfusates. Unilateral electrical stimulation of the cerebral motor cortex (area 4) induced a long-lasting and similar activation of [3H]DA release in both caudate nuclei. The activation of [3H]DA release in the contralateral side was selectively abolished after acute transection of the rostral part of the corpus callosum. This transection also suppressed the flexion of the contralateral forelimb induced by the stimulation. The activation of [3H]DA release could be related to the stimulation of corticostriatal neurons which may interact directly or indirectly with dopaminergic terminals in both caudate nuclei. Unilateral electrical stimulation of the visual cortex (areas 18 and 19) markedly stimulated the release of [3H]DA in the ipsilateral caudate nucleus. A slight effect was seen in the contralateral structure 20 min after the stimulation. These results are consistent with the existence of a main ipsilateral pathway originating from the visual cortex and projecting directly to the striatum. Both types of electrical stimulation immediately activated the release of [3H]DA in the ipsilateral substantia nigra. These effects were still seen 20 min after the stimulations. The activation of the dendritic release of [3H]DA could be related to the stimulation of a corticonigral projection. These results further indicate that the nigrostriatal dopaminergic neurons may be involved in sensory motor integration.