Excretory liver function was analyzed in 10 healthy volunteers and 28 subjects with acute or chronic liver injury following intravenous administration of 99mtechnetium p-isopropyl iminodiacetic acid. Hepatobiliary transit of this agent was quantitated at 5-min intervals for a total of 60 min. Indices of total liver activity, liver cell uptake, liver parenchymal clearance, and bile duct clearance of 99mtechnetium p-isopropyl iminodiacetic acid were calculated from time--activity curves over heart, liver, extrahepatic bile ducts, and gallbladder. Seven subjects with acute viral hepatitis, 15 with extrahepatic biliary obstruction, and 6 with intrahepatic cholestasis were evaluated. Compared with healthy volunteers, a significant (p less than 0.0001) reduction in total liver activity and liver parenchymal clearance was demonstrated in all patient groups. Major resolution in all liver-derived indices, particularly total liver activity, occurred during convalescence from hepatitis and after biliary drainage. Nonmeasurable bile duct clearance always indicated a diagnosis of extrahepatic obstruction in cholestatic subjects, and this index normalized in subjects following biliary drainage. Whereas visual assessment of 99mtechnetium p-isopropyl iminodiacetic acid scans provided limited, useful information about the functional status of the liver, quantitative temporal analysis proved to be a much more effective technique.