With the purpose to elucidate the properties of the thoracic duct lymph during the production of bile pigment in vivo, the author pursued the changes in the amounts of easily-split-off iron and free iron in lymph and in hemoglobin content by creating thoracic duct fistula in normal dogs, in dogs administered carbon tetrachlorice or in dogs occluded of RES, and then by lording physiological saline solution or hemoglobin solution into the femoral vein or peritoneal vein of these animals, and compared these results with contents in blood. The following are the results. 1. In the normal dogs the content of easily-split-off iron in lymph increases transiently later than that in blood, but the changes in both are somewhat parallet to one another. 2. In the case with liver disorders the increase in the blood easily-split-off iron is slow or undetectable, while on the contrary, the easily-split-off iron in lymph increases slower than in normal animal but distinctly. 3. Since a large quantity of the injected hemoglobin is transferred to lymph in the case with liver disorders, the major portion of easily-split-off iron produced due to the liver disorders, though the amount produced is trivial, seems to be transferred to lymph. 4. In the case occluded of the RES the increase of easily-split-off iron in lymph is slow and small in amount. 5. The easily-split-off iron in lymph is the one produced in the liver from hemoglobin and then transferred to lymph, while the easily-split-off iron in blood is also a portion of the same produced in the liver but transferred directly to blood.