A radiological technique to image the gallbladder, rendered largely historical and superseded by good ultrasonography. An orally adminstered contrast agent, usually an iopanoic acid derivative, is secreted and concentrated in the gallbladder. The gallbladder is imaged by plain abdominal radiography. As most (90%) gallstones are radiolucent, the gallstones appear as translucent defects within the contrast-filled gallbladder. Biliary obstruction or other disruption to the entero-hepatic circulation may result in non-diagnostic results.