Tyrosine hydroxylase (TH, EC, glutamate decarboxylase (GAD, EC, and choline acetyltransferase (ChAT, EC, activities were used as markers of the presence of catecholaminergic, GABAergic, and cholinergic neurons in human brain. The disparity in the absolute values obtained in control caudate nucleus led us to study the pattern of distribution of these enzymes in given brain regions, with the idea that the pattern might be altered specifically in pathological conditions. The tridimensional distribution of TH, GAD, and ChAT activities was investigated within the caudate nucleus, the putarnen, and the pallidurn. In control patients, opposite rostro-caudal and rnedio-lateral gradients appeared for GAD and CAT; ChAT activity was higher at the caudal level and GAD activity was higher at the rostral level of caudate nucleus and putamen. In the medio-lateral extent of putarnen and pallidurn, ChAT activity was highest in the lateral part of the putarnen; GAD was highest in the medial segment of the pallidum. Only GAD presented a particular dorsoventral pattern, the enzyme activity being highest in the ventral part of the caudate nucleus and the putarnen. No reproducible distribution was observed for TH. In Parkinsonian patients, a decrease of TH and GAD activities with abolition of gradients was observed, whereas the ChAT activity and pattern were not modified.