Sincalide-aided ultrasonography of the common bile duct as a predictor of biliary obstruction determined by ERCP and biliary manometry. Sonographically observed changes in common bile duct caliber following intravenous sincalide injection were correlated with distal common duct pathology as defined by endoscopic retrograde cholangiopancreatography and biliary manometry. Thirty-two patients, 17 with prior cholecystectomies, were studied. In post-cholecystectomy patients, a 1-mm or greater diminution of duct caliber within 5 min represented a normal response. When gallbladder contraction occurred in normal patients with an intact gallbladder, no change or a diminution in duct caliber was observed. When gallbladder contraction was not observed, a normal response was considered to be the same as that in post-cholecystectomy patients with a diminution in duct caliber occurring. By using these criteria two false negatives, both with hypertensive sphincters of Oddi that responded normally to sincalide injection, were encountered. This technique was valuable in defining non-obstructed post-cholecystectomy dilated bile ducts which demonstrated a prompt diminution in caliber following sincalide injection. 