The need to differentiate patients with acalculous gallbladder disease who would benefit from cholecystectomy and those who would not led to the search for a procedure that would be of value in this respect. For this purpose, cholecystokinin (CCK) has been used, and many reports have indicated that CCK does identify patients in whom the gallbladder is the source of pain. A review of papers dealing with CCK as a diagnostic aid suggests, however, that some radiographic evaluations have not been subjected to adequate, unbiased interpretation and that some follow-up studies have been incomplete and of short duration. Despite these objections there is evidence that CCK can be useful as a diagnostic aid, and further, continued, well-designed studies are indicated.