Operative roentgenographic cholangiography entails problems during pregnancy because of the hazard of radiation to the fetus and mother. In 450 biliary tract operations in which real-time B-mode operative ultrasonography was performed, five were for diseases of the biliary tract during pregnancy. Operative ultrasound correctly revealed non-palpable stones in the gallbladder in one patient and in the common bile duct in three patients. Furthermore, operative ultrasound provided anatomic information, such as dilation or stenosis of the common bile duct. Of seven possible occasions in which roentgenography would customarily be expected to be performed, operative cholangiography was used only once. Thus, ultrasound significantly reduced the number of operative roentgenographic studies. Operative ultrasonography was not associated with any complications and significant time delays. It is concluded that operative ultrasonography can replace operative roentgenographic cholangiography as a screening procedure for gallbladder and common duct calculi at biliary tract operations during pregnancy.