In 1925 Rosenthal and White introduced a bromosulfophthalein (BSP) dye retention test as a sensitive indicator of liver function. Even now it is regared as one of the most sensitive agents for the detection of non-icteric liver disease (liver cirrhosis, early stage of acute-hepatitis and hepatic tumor). BSP accumulates in the liver cells, conjugates with glutathione and is excreted into the bile. Therefore, a disorder in its excretion is due to a disturbance of one of these processes. Since bilirubin and BSP compete for uptake by the liver and increased serum bilirubin interferes with the colorimetric determination of BSP, it has been considered that BSP test is inappropriate for the differential diagnosis of jaundice conditions. It has been generally said that when jaundice is present, the BSP test is useless and should not be performed. In 1955, Taplin et al. labeled rose bengal, a dye similarly metabolized in the liver as BSP, with 131I and measured the hepatic excretion of this dye by external monitoring. Laster, Blahd et al. applied this method to the determination of the peripheral pool, succeeding in the diagnosis of chronic and subacute hepatic diseases without colorimetry. In 1968, Yamada, Taplin et al. suggested the possibility of differentiating so-called medical jaundice from surgical jaundice by scanning the subjects during 24 to 48 hours following intravenous injection of 131I-labeled rose bengal. As mentioned before, many authorities hold the opinion that BSP is not proper for the differential diagnosis of jaundice states. Some have tried to diagnose biliary tract obstruction by a malignant tumor by measuring BSP excretion into duodenal fluid and others by quantitating changes in serum levels of conjugated and free BSP. Furthermore, Burton et al. reported that in patients with extrahepatic obstructive jaundice, BSP retention was observed for 24 days after its administration. From a consideration of all these finding we came to a conclusion that the differential diagnosis of various jaundice states, (medical, surgical and constitutional) is possible by sequential scanning with radioisotope-labeled BSP, as with rose bengal, in accordance with procedures described by Yamada, Taplin et al. The evidence suggested that labeled BSP might make a more important contribution than rose bengal.