Intravenous injection of 2% normal saline solution of Congo red in a dosage of 5 cc/kg in a dog resulted in marked increase of lymph flow from the thoracic duct over several hours and the lymph was apparently less coagulable after injection of the dye. In a majority of cases, arterial pressure showed only a slight fall by this injection, while portal pressure showed a marked elevation accompanied with an increase of liver volume. Such changes in the flow of lymph and circulation could not be reproduced by the injection of a saline solution isosmotic with the dye solution. Appearance of a fairly large amount of hemoglobin in the plasma and lymph after injection of the dye solution was observed by spectrophotometer. This hemolysis was completely protected by the previous injection of heparin into the vein before injection of the dye solution but the increased flow of lymph and elevation of portal pressure effected by the dye solution could not be modified. In a dog administered with heparin to remove the effect of hemolyis, injection of the dye solution was observed to cause increase in refractive index of the lymph and decrease of the same of the plasma. This is an indication that a large amount of plasma protein had filtrated into the lymph. After injection of the dye solution, histamine content in the lymph was practically unchanged. Antihistamines failed to suppress the increased flow of the lymph and elevation of portal pressure. In a non-heparinized dog, appearance of a substance or substances assumed to be adenine nucleotides was observed in the plasma by spectrophotometry and paper chromatography immediately after injection of the dye solution. It was concluded from these results that the increased flow of the thoracic lymph caused by Congo red is related to congestion of blood in the liver and other organs in the abdominal cavity, and further it was deduced that the cause common to these phenomena is not blood coagulation and liberation of toxic substances (including adenine nucleotides) from blood cells into plasma, which are considered to be the cause of acute dye shock, but is some kind of injuries to peripheral vessels, especially to vascular system in the abdominal organs.