Cat caudate nucleus (CD) neurons were tested for changes in spontaneous activity, response to peripheral sensory stimuli (tactile, auditory, and visual), and electrical stimulation of monosynaptic afferents (pericruciate cortex and nucleus centralis lateralis) in normal cats and in the same cats after induction of and spontaneous recovery from parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). After normal baseline data were collected, cats were given MPTP (7.5 mg/kg, 5–7 d) to induce a parkinsonian syndrome consisting of rigidity, akinesia, and decreased orienting to sensory stimuli. During this symptomatic period, the mean spontaneous activity of CD units increased (6.20 spikes/sec vs 2.25 spikes/sec in normal cats). In these same animals, the percentage of units responding to peripheral sensory stimulation was significantly decreased (compared to normal) while the percentage of units responding to electrical stimulation of monosynaptic afferents increased. By 6 weeks after MPTP administration, cats had recovered gross motor and sensorimotor function and CD unit recordings were reinitiated. In functionally recovered animals, all electrophysiological measures returned to levels resembling those seen in normal animals. These data suggest that the processing of peripheral sensory information is an important part of basal ganglia function and that the sensory responsiveness of the CD may reflect the overall motor condition of the animal. The changes observed in the responsiveness of CD neurons to direct electrical stimulation of monosynaptic afferents may indicate that the defect in the processing of polysynaptic sensory information observed in the striatum in parkinsonian animals may be occurring, at least in part, extrastriatally.