After a short introduction (chapter 1), anatomy is described in chapter 2. The sphincter of Oddi (SO) can be divided into the choledochal, pancreatic and ampullar sphincter in addition to the intermediate fibres. In anatomic studies the pancreatic and ampullar sphincters are described in only one third and sixth respectively. This is in disaccordance with manometric studies where SO activity always is registered in the pancreatic sphincter after total biliary sphincterotomy. Chapter 3 discusses whether or not the SO is a true sphincter. Activity simultaneous with the duodenum occurs in the interdigestive phase III, but more often duodenal and SO activity is dissociated. It is concluded that the vast evidence supports the SO as a true sphincter. Chapter 4 concerns methods for investigation of the SO activity. The manometric methods are divided into direct and indirect studies, and advantages and disadvantages are discussed. The direct manometric method employing a perfusion system is highlighted, and interpretation of tracings and artifacts described. In chapter 5 physiological aspects are considered. Slow waves are present in the SO, and the activity related to the migrating motor complexes of the duodenum. Apart from interdigestive variation the food stimulated pattern is mentioned. Nervous and hormonal control as well as the relation to other parts within and outside the pancreatico-biliary system is outlined. The SO receives nervous fibres from both the sympathetic and the parasympathetic system. The alfa- and cholinergic neurons stimulate whereas the beta-neuron inhibits the SO. Furthermore inhibitory non-adrenergic, non-cholinergic neurons are present. Cholecystokinines inhibitory action on the SO are brought about via a stimulation of inhibitory neurones since the peptide has a direct stimulatory action on the SO muscle. The most important reflex regulation of the SO is elicited by gallbladder pressure increase with inhibition of the SO. Probably a similar reflex relationship exists between the common bile duct and the SO. The SO is considered important in the regulation of biliary flow, and probably also pancreatic flow, although the latter is only poorly studied. Furthermore the SO is believed to play a role in the prevention of reflux from the duodenum. In chapter 6 studies in normals, controls and patients with diseases in the biliary and pancreatic system are surveyed. In patients with gallbladder stones no changes in SO activity has been disclosed. In patients with common bile duct stones some have found increased antiperistalsis, others not.(ABSTRACT TRUNCATED AT 400 WORDS)