Cholecystokinin is a linear polypeptide containing 33 amino acids. Among the tryptic degradation products of the molecule, the C-terminal octapeptide is known to be highly active. In the present study, the synthetic C-terminal octapeptide of cholecystokinin was administered to 50 patients referred for cholecystograph. The preparation was found to have a shorter duration of action compared to extracted cholecystokinin, but produced evacuation of the gallbladder and visualization of the bile ducts without any harmful side effects. The synthetic C-terminal octapeptide of cholecystokinin may be expected to be a valuable alternative to extracted preparations that are not available at present in amounts sufficient for routine clinical use.