Stimulation of the caudate nucleus at either, 7 Hz or 100 Hz impaired performance of a complex motor task. The disruptive effects on execution of the task occurred at low amperages and appeared to involve interference with temporal programming of response components. Task initiation was impaired by stimulation at higher amperages. Electrical stimulation of anterior sites in the caudate nucleus resulted in impairment of performance at lower stimulation intensities than did stimulation of posterior sites. Although stimulation (7 Hz) of hippocampus, nonspecific thalamic nuclei, or mesencephalic reticular formation also resulted in performance deficits, the topography of interference effects and the threshold intensities required for disruption were different from those resulting from stimulation of the caudate nucleus.