We systematically studied the intramural nervous system of the alimentary tract in patients with Parkinson's disease and found that Lewy bodies were distributed widely in the Auerbach's and Meissner's plexuses. In the central nervous system, we recognized a striking similarity between the distribution of Lewy bodies and that of monoaminergic neurons. More recently, we have demonstrated that neuronal somata immunoreactive for tyrosine hydroxylase (TH) exist in the Auerbach's and Meissner's plexuses of normal humans. We consider a possible relation between these TH-immunoreactive catecholaminergic neurons to the occurrence of Lewy bodies in the enteric nervous system in Parkinson's disease. The affinity of Lewy bodies to the central and enteric neurons seems to be attributable to an unknown cell-biological characteristic apparently shared by both neurons.