Studying the formation process of the bile pigment in vivo with reference to the vicisitude of the bile pigment in the bile following the administration of the docompositions of hemoglobin into the portal vein of the rabbit with artificial biliary fistula. And the following results were obtained. 1. Following the administration of saline into the portal vein, production of the bile pigment in the liver was transiently depressed and then increased because of choleretic action of saline. 2. Following the administration of verdohemochrome solution, which was decomposed into biliverdin and, in part, was deoxidized to bilirubin. verdohemochrome was excreted in the healthy cases. The decomposition process was prolonged or less in the cases with blocked reticuloendothelial systems, and little decomposition was observed in the cases with liver impairments. 3. Following the administration of biliverdin solution to the healthy cases, the majority of biliverdin was excreted unchanged but part of it was deoxidized to bilirubin. There was no such evidence in the cases with blocked reticuloendothelial system and was very slight degree in the cases with liver impairment. In consequence, the deoxidation of biliverdin was presumably due to reticuloendothelial system. However, in the cases with blocked reticuloendothelial system or liver impairment, it was supposed that biliverdin was excreted from the liver and easily deoxidized into bilirubin.