The following protocols should be observed in evaluating a patient with suspected cholecystitis: In evaluating chronic cholecystitis in patients on a diet containing fat, plain films of the abdomen and oral cholecystogram are the procedures of choice. If the gallbladder fails to fill after ingestion of 3 g iopanoic acid, the procedure is repeated with an additional 3 g the following day. Failure of the gallbladder to visualize after a two-day study, equivocal findings, or persistent symptoms despite a normal study should be followed by ultrasound and, if necessary, cholescintigraphy. The latter two studies should be done in a fasting state, and CCK used to demonstrate gallbladder contraction during both tests. In suspected acute cholecystitis, plain radiography, ultrasound, and Tc-99m-imino diacetic acid derivative scanning should be performed. Again CCK should be used during cholescintigraphy to verify nonvisualization and to stimulate gallbladder emptying.