Auditory feedback is necessary to maintain singing in the adult male Bengalese finch (songbirds/oscines). Their song patterns are altered within a month following cochlear removal-induced deafness. Stabilization of song patterns occurs thereafter. To clarify what kind of changes appear in the brain of deafened birds, we examined immunohistochemically the expression of protein kinase C (PKC), considered a molecular marker for synaptic plasticity, in the robust nucleus of the archistriatum (RA), one of the song control nuclei in the forebrain of finches. Two weeks after cochlear removal, immunoreactive fibers and terminals in the RA transiently increased, and thereafter tended to decrease gradually. Moreover, the degree of song alteration and stability paralleled these changes in the RA. The immunoreactivity of the RA remained unchanged in intact birds. These results indicate that surgical deafening increases the expression of PKC in the RA. These changes in the RA are related to the alteration of song patterns in the deafened adult Bengalese finch.