Cholinergic neuropil and cell bodies were identified in the human striatum by immunohistochemistry carried out with a polyclonal antibody raised against choline acetyltransferase (ChAT). The cholinergic neuropil was not uniformly distributed in the striatum, and especially in the caudate nucleus ChAT-poor zones corresponding to acetylcholinesterase (AChE)-poor striosomes were identified. Striosomal organization of ChAT-positive neuropil was also detected in striatal tissue from patients who had suffered parkinsonian and choreic disorders.