Irrigation experiments were performed on the liver of rabbit determining bilirubin and biliverdin in the bile and irrigating solution, and the following results were obtained. 1. Upon irrigation with hemoglobin added blood, bilirubin was not detected from the irrigating solution, however, the excretion of biliverdin and indirect bilirubin resulted from decomposition of hemoglobin, was observed. It is hard to determin whether these biliverdin and indirect bilirubin really stemmed from hemoglobin or from hemolysis during the irrigation. The reticuloendothelial system in the liver and liver cells played important roles in the formation of biliverdin and indirect bilirubin from hemoglobin. 2. Upon irrigation with verdohemochrome added blood, the verdohemochrome was easily decomposed into biliverdin and bilirubin. They were excreted into the bile, and reticuloendothelial system and liver cells would be involved in these depositions. 3. Upon irrigation with biliverdin added blood, over a half of the biliverdin was excreted into the bile. The excreting biliverdin was found to be two forms, the one was biliverdin without any change and the other was bilirubin deoxidized from biliverdin. In the cases with impairment of reticuloendothelial system and/or of liver cells, the excretions of these pigments were rather accelated. The process of the deoxidization of biliverdin into bilirubin took place not only in reticuloendothelial system but even after the excretion from the liver into the bile ducts. 4. In the mechanism of bile pigment formation, not only the reticuloendothelial system played an important role but the liver cells did.