The distribution of parvalbumin in the basal ganglia was studied in eight human brains using immunohistochemical techniques and the pattern of staining was compared to the distribution of enkephalin immunoreactivity in adjacent sections. The results showed a heterogeneous pattern of parvalbumin immunoreactivity in the caudate nucleus and putamen; this pattern of staining was characterized by irregularly shaped patches of low parvalbumin immunoreactivity dispersed against a background matrix of moderate-to-high immunoreactive staining. These parvalbumin-poor patches in the caudate nucleus and putamen aligned with the enkephalin-rich striosomes. These results show that parvalbumin immunoreactivity in the human striatum has the same compartmental mosaic organization as other neurochemical markers in the mammalian striatum.