The aim of this study was to review critically the diagnostic features of intestinal neuronal dysplasia type B (IND B). Over a period of 5 years colonic mucosal biopsies of 773 children with symptoms of chronic constipation were examined. Four biopsies taken 2-10 cm above the pectinate line were cut in serial sections and histochemical lactate dehydrogenase, succinate dehydrogenase, (SDH) and acetylcholinesterase (AChE) reactions performed. Presence of giant ganglia of the submucosal plexus, being characterized by more than seven nerve cells, established the diagnosis of IND B. Giant ganglia were found to be age-independent changes, while hyperplasia of the submucosal plexus, increase of AChE activity in nerve fibres of the lamina propria and low SDH activity in nerve cells proved to be age-dependent findings which disappear during the maturation of the enteric nervous system. Using these criteria IND B was diagnosed in 209 children. In 64 of these patients a combination of IND B and aganglionosis (Hirschsprung's disease) was found. IND B seems to be related to premature expression of laminin A during embryogenesis, resulting in premature nerve cell differentiation in the myenteric and submucosal plexus, which in turn blocks neuroblast colonization of the rectum. IND B, hypoganglionosis and aganglionosis, which are often combined, may therefore be considered to be different manifestations of the same developmental abnormality.