Recent investigations have demonstrated the colonization of NOS-immunoreactivity and NADPH-diaphorase staining in central and peripheral neurons. The current study investigates the presence and distribution of NADPH-diaphorase-stained nerve cells and fibres in whole-mount preparations of the enteric nervous system of the human colon. Numerous NADPH-diaphorase-stained nerve cell bodies were found in the plexus myentericus and in the plexus submucosus externus. In contrast, we found but very few NADPH-diaphorase-stained nerve cells in the plexus submucosus internus. The majority of the NADPH-diaphorase-stained nerve cells had morphological characteristics similar to those of the Dogiel type I neuron, i.e. possessing broad flat dendrites and one major axonal projection. NADPH-diaphorase-stained nerve fibres can be observed in all three ganglionic networks and in the aganglionic plexus of the circular muscle layer.