Sincalide, the C-terminal octapeptide fragment of the cholecystokinin, was used to contract the gallbladder during routine oral cholecystography in 18 patients. In 14 patients clinically important contraction occurred. The average reduction in gallbladder size for these patients was 32.7% of the preinjection size (range 15.1%-67.9%). Within 8-12 minutes cystic duct visualisation occurred in 8 and common bile duct visualisation in 3 patients. Spasm of the gallbladder neck was found in 2 cases. The blood pressure and heart rate did not change significantly during the study. Six patients felt slight nausea for 1-4 minutes and two vomited. We conclude that sincalide may be useful in biliary tract function studies in special clinical conditions (i.e. upper abdominal pain with unknown aetiology).