We found in the adult rat that a small number of striatal neurons showed aromatic L-amino acid-like immunoreactivity. These neurons had a cell body with 10-20 microns diameter and several spiny dendrites, and were distributed throughout the striatum (the caudate nucleus and putamen) without any particular topography. The number of these neurons was increased on the side ipsilateral to an electrothermic or 6-hydroxydopamine-induced lesion which had been placed in the midbrain regions around the substantia nigra pars compacta.