Previous anatomical studies have described a distinct sphincteric structure at the entrance of the common bile and pancreatic ducts in the duodenum. However, from an anatomical point of view, the pancreatic duct sphincter is only present in one third of human specimens. The purpose of the present study was therefore to investigate whether sphincteric activity could be demonstrated in patients in whom the common bile duct sphincter was completely transsected during endoscopic sphincterotomy. Twelve patients had a complete bile duct sphincterotomy because of sphincter of Oddi dyskinesia. The sphincterotomy was checked manometrically in all, and neutralization of the choledochoduodenal gradient recognized. In all patients a distinct pancreatic sphincteric zone with base-line elevation and superimposed phasic activity was demonstrated. In six patients the pancreatic duct sphincter was studied before and after bile duct sphincterotomy, and, although a definite sphincter zone still was present in the pancreatic duct, a reduction in phasic wave amplitude was observed. A similar decreased base-line and pancreatic duct pressure was observed, although not statistically significant.