Sphincter of Oddi motor activity was investigated in seven patients with an anomalous pancreaticobiliary junction and in six controls by endoscopic manometry under fluoroscopy. Characteristic phasic wave activity was observed in the sphincter segment in both groups. Amplitude of the phasic contractions was significantly higher in the disease group than in controls (100.8 +/- 14.1 mm Hg vs. 55.2 +/- 4.3 mm Hg, p less than 0.02). Although those with the anomalous pancreaticobiliary junction had a longer common channel (15-30 mm), the length of the sphincter segment with the phasic wave activity was not different. The phasic activity was not seen at the junction of the pancreatic and bile ducts in disease groups. Bile obtained from within the bile duct showed a very high concentration of amylase. Morphine given to cause spasm of the sphincter increased basal pressure and frequency of the phasic waves in all controls. The response to morphine was similar in two patients in whom the anomalous junction was studied, but the procedure was complicated by acute pancreatitis in one of them. These findings suggest that contractions of the sphincter of Oddi in patients with the anomalous junction may contribute to reflux between the pancreatic and bile ducts, leading to various pathologic conditions associated with this anomaly.