Technetium-99m IDA cholescintigraphy has provided a new, noninvasive means of visualizing biliary tract function. It has become the procedure of choice in patients with suspected acute cholecystitis because of its ability to most accurately detect functional obstruction or patency of the cystic duct as opposed to ultrasound's ability to detect only anatomic changes such as the presence of calculi or a thickened gallbladder wall. These latter findings are more important in establishing the diagnosis of chronic cholecystitis where ultrasound shares a position of prime importance with the oral cholecystogram. Tc-99m IDA cholescintigraphy has also been particularly useful in evaluating bile leaks, biliary-enteric anastomosis patency and the post-cholecystectomy patient with recurrent pain. In the patient with cholestasis, ultrasound is usually the procedure of choice since it establishes whether or not ductal dilatation is present and frequently can determine the cause of obstruction. Cholescintigraphy has played an ancillary role in many cases by demonstrating the level of partial obstruction, but it does not have the anatomic resolution to visualize the cause of obstruction. Occasionally, in the evaluation of cholestasis, cholescintigraphy has proven to be the only modality which has identified the presence of acute common duct obstruction or localized intrahepatic ductal obstruction. All in all, Tc-99m IDA cholescintigraphy has had a dramatic impact upon hepatobiliary diagnosis.