The object of the present study was to improve the accuracy of measurements of ileal function obtained by abdominal scanning and fecal counting after oral administration of the gamma-labeled bile acid 75seleno-homocholic acid-taurine (75SeHCAT), as current techniques do not distinguish between retention of the bile acid within the enterohepatic circulation from retention within the colon, and are also affected by incomplete stool collection when using the fecal method. We have therefore introduced the following modifications: (a) simultaneous ingestion of 51CrCl3 as a nonabsorbable correction marker for both the abdominal scanning and fecal counting methods; and (b) the use of 75SeHCAT counts over the gallbladder area on abdominal scanning, because these counts should be independent of colonic retention. We have studied 42 subjects, including 6 healthy controls, 6 ileal resection subjects, 15 ulcerative colitis patients, and 15 patients with unresected ileal Crohn's disease. Colonic retention (0%-68% per day) caused a variable overestimate of 75SeHCAT absorption. Corrected measurements of the fecal absorption index determined by a gamma-counter and of the abdominal absorption coefficient determined by a gamma-camera correlated well with each other (r = 0.92, p less than 0.0001), providing an internal validation of the 51CrCl3 modification. The fecal absorption index could also be determined from the carmine-rich stool collection of a single day, and this also correlated well with the abdominal absorption coefficient (r = 0.81, p less than 0.0001). Gallbladder scanning alone was simpler, involving only one isotope, but it correlated less well with the fecal absorption index than did the abdominal absorption coefficient (r = -0.64, p less than 0.001).