The purpose of this study is to increase the diagnostic significance of an initially “nonvisualized gallbladder.” Failure to visualize the gallbladder during a routine oral cholecystography is only presumptive evidence of gallbladder disease. For any number of reasons (2, 6) a normal gallbladder may not be visualized on the cholecystogram. Immediate administration of ipodate4 calcium to all patients who had an initially nonvisualized or poorly visualized gallbladder has, in our experience, significantly increased the percentage of positive diagnoses. In some cases it provided a good study of the common bile duct and reliable evidence of cystic duct obstruction. The calcium salt of ipodate is rapidly absorbed from the gastrointestinal tract and can be seen in the biliary tree and in the gallbladder within two or three hours after ingestion (3, 4, 7, 8). Thus, it provides further diagnostic information quickly and without necessity of intravenous injection. We shall describe our procedure for both routine cholecystography and immediately repeated cholecys–tography and shall present the results of re–examina–tion of 201 patients with initially nonvisualized gallbladder. Procedures Particular attention is paid to proper preparation of the patient and to optimum roentgenographic technic at all times. Routine Cholecystography: On the day before examination the patient eats a fatty meal at noon in order to promote satisfactory emptying of the gallbladder. The evening meal is light and fat–free. At 7:00 P.M. the patient is given 6 capsules (3 g) of ipodate sodium. At 10:00 P.M. a laxative (15 mg of Dulcolax) is given orally to eliminate fecal matter which might obscure the gallbladder area. On the morning of the examination, the patient eats no breakfast and reports to the x–ray department at 7:00 A.M. A film of the right upper quadrant and of the entire abdomen is taken and develloped immediately. If the gallbladder is not visualized or is poorly visualized on these films, the examination is repeated. Repeat Cholecystography: The patient is given 3 g of ipodate calcium granules dissolved in a glass of water and is placed on a stretcher, lying on the right side. An additional glass of fluid (water or orange juice) is given to speed emptying of the stomach. Films of the right upper quadrant are made one, tw o, three, and four hour s after ingestion of the contrast medium. If, after four hours, the gallbladder st ill is not visua lized in the right upper quadrant, a film of the entire abdomen is obta ined, in case th e gallblad der is abnormally located. The patient is told to remain on a strict fat–free diet and return the next day for a twenty–four hour follow–up study.