The postnatal development of the myenteric plexus in cat stomach has been studied at birth, on the 14th, 30th, 45th and 180th postnatal days, using light- and electronmicroscopic methods. In newborn kittens the main network of the Auerbach plexus is well formed, but the myenteric ganglia are composed of nerve cells with different maturity and a scarce neuropile. During the first two postnatal weeks the dimensions of the ganglia increase owing to the increase of the nerve bodies and the rising number of glials cells and intercellular fibres. This is accompanied by a potentiation of the AChE-activity, mainly in the nerve cell bodies and to a lesser extent in the neuropile. Impregnation reveals different in calibre and form nerve fibres and terminals. Different ultrastructural types of neurones are identified on the 14th day. Later development is expressed in the formation of large compact ganglia and thick connecting strands. The number of AChE-positive fibres in the neuropile increases. Owing to the increase in the cell organelles and their more advanced maturity, it is possible to define the ultrastructural type of an ever increasing number of neurones.