• Cholangiography can be performed during operations on the biliary system by injecting the contrast medium through the cystic duct before exploring the common duct or by injecting through the T-tube after exploration. The film is exposed during a brief period of apnea induced by the anesthesiologist, and while the film is developed the gallbladder can be removed. Cholangiograms with sodium acetrizoate as the contrast medium were made in 444 patients. The common duct was explored in 231, and calculi were recovered from the ducts in 115. Stones missed on operative exploration were detected by operative cholangiography in 36 patients. Post-operative complications have occurred, and both false-positive and false-negative results have been noted. These difficulties can be reduced by attention to details, and the usefulness of the results has been demonstrated.