Since its introduction in the early 1950's, Cholografin has become widely accepted and is being used with increasing frequency. Although its primary indication is in the postcholecystectomy patient, certain conditions necessitate its use for the initial evaluation of the biliary system. Cholografin methylglucamine2 provides 52 per cent iodipamide methylglucamine and the bound iodine content of the solution is about 26 per cent (5.2 gm. per 20 c.c.). Approximately 90 per cent of the Cholografin injected is excreted by the liver and the remaining 10 per cent by the kidneys. It appears in the bile almost immediately after injection; however, the best ductal visualization is obtained in twenty to thirty minutes. Filling of the bladder is produced by an overflow of the contrast-laden bile from a tightly filled common bile duct. The medium passes concentrically around the wall of the gallbladder with subsequent diffusion and mixing into the nonopacified bile. This is a passive filling and does not reflect on the concentrating power of the gallbladder. The visualization of the gallbladder commences within half an hour after the injection, and the density of the shadow gradually increases to a maximum at about two hours. Simultaneous excretion by the liver and kidney has been noted without apparent liver disease and with no decrease in intensity of the bile duct shadows. Stratification has been described in several of the earlier reports on Cholografin (1–6). The incidence is unknown, but little emphasis has been placed upon this phenomenon in the past several years. It is the purpose of this paper to re-emphasize its importance in avoiding certain errors of interpretation. This is exemplified in the following case report. Case Report A 41-year-old white female was admitted to Georgetown Hospital with severe pain in the right upper quadrant. For the past two years, she had experienced intermittent right-upper-quadrant pain, associated with nausea and occasional vomiting but not related to food intake. On physical examination, tenderness was present in the right upper quadrant and the periumbilical region. No other abnormalities were noted, and all laboratory studies were normal. Intravenous cholangiography was done, with good visualization of the ductal system and gallbladder on the supine films, and no evidence of calculi. Twenty minutes following a fatty meal, upright compression spot-films demonstrated a layering effect. This was interpreted as small floating gallstones (Fig. 1). A cholecystectomy was performed and no calculi were found, but there were changes consistent with chronic cholecystitis. Comment: In previous reports, including radiographs, this zone of layering was much wider, with less distinct borders, than in our case.