Cholangiography and cholecystography were performed in fasted dogs and human subjects using sodium iopanoate given intraduodenally in doses of 10 and 20 mg/kg. The same studies were performed after intraduodenal administration of fat or after intravenous administration of cholecystokinin (CCK) in dogs and after a fatty meal, to stimulate endogenous release of CCK, in human subjects. In both the animals and human subjects, peak blood iodine concentrations were reached by 30 minutes after iopanoate administration. At a dose of 10 mg/kg, radiographic visualization of both bile ducts and gallbladder was inconsistent. At 20 mg/kg (one-half the clinical dose for standard oral cholecystography,) the common bile duct was visualized within 60 minutes and the gallbladder within 90 minutes. Gallbladder density increased over the next 6 hours. Prior administration of fat or CCK led to earlier and denser gallbladder opacification. The common bile ducts opacified with the use of iopanoate were small in caliber, averaging only 3 mm. This probably reflects the fact that, unlike iodipamide, iopanoate has little or no choleretic effect. Therefore, because it would not increase the volume of bile in the duct, iopanoate would not increase duct size.