It has been postulated that cholecystokinin sonography may be useful in the diagnosis of acute acalculous cholecystitis in the hospitalized patient. To evaluate this hypothesis, sincalide, a cholecystokinin derivative, was administered to 15 fasting trauma patients who had undergone laparotomy. No biliary or gallbladder disease was found in any patient. Sincalide was slowly administered intravenously, and the gallbladder was examined with ultrasound every 5 minutes for 60 minutes. The average decreases in length, height, and width of the gallbladder were 15%, 23%, and 21%, respectively. In only four of the 15 patients was there a decrease by more than 50% in any of these dimensions. The average decrease in gallbladder volume was 33% (range, 0%-97%), with no change in gallbladder volume in four patients. There is considerable variability in gallbladder response to administration of sincalide in the fasting hospitalized patient. Lack of contraction of the gallbladder after injection of cholecystokinin should not be considered a major criterion in the diagnosis of acute acalculous cholecystitis.