Pharmacological intervention with either cholecystokinin-8 (CCK-8) or morphine during 99mTc- hepatoiminodiacetic acid (HIDA) cholescintigraphy is required primarily for the assessment of the diseases affecting the gallbladder, the common bile duct, or the sphincter of Oddi. For imaging, the patient should be prepared by an overnight fast, or with 4 hours of minimum fast. Pre-emptying with CCK-8 is probably undesirable and should either be avoided or one should wait for at least 4 hours after CCK-8 to begin the 99mTc-HIDA study to achieve higher specificity of the test for acute cholecystitis. When he gallbladder is not observed by 60 mins in a clinical setting of acute cholecystitis, a dose of 0.04 mg/kg of morphine is administered intravenously and imaging continued for an additional 30 mins. Nonvisualization of the gallbladder by 90 mins with morphine in an appropriate clinical setting is diagnostic for acute cholecystitis. When the gallbladder is not observed by 60 min but is seen with morphine administered after 60 mins, a positive diagnosis of abnormal gallbladder function can be made. When the gallbladder is observed in a clinical setting of biliary pain or chronic calculous or acalculous cholecystitis, CCK-8 at a dose rate of 3.3 ng/kg/min is infused intravenously for 3 mins (10 ng/kg/3 min) for the measurement of the ejection fraction. An ejection fraction value of less than 35% is indicative of calculous or acalculous chronic cholecystitis. The gallbladder emptying is directly related to the total number of cholecystokinin receptors in the smooth muscle. The ejection fraction can be controlled to any desired level simply by controlling the dose rate or the duration of infusion of CCK-8. Morphine and other opiate metabolites circulate for many hours in blood and act on the sphincter of Oddi and decrease the gallbladder ejection fraction. Careful drug history, especially that of opiates, is very critical in all subjects with a low ejection fraction before assigning an abnormality to the gallbladder motor function.