Book excerpt: This book first presents an overview on the chemical coding of the morphological neuron types described by Stach in the pig intestine. In doing so, we have pointed out the difference between the definitions of type I neurons given by Dogiel and Stach. Secondly, it provides a basis for the morpho-chemical classification of human enteric neurons as revealed by their immunoreactivity for neurofilaments and several neuroactive substances or related markers.