In order to analyze the mode of lymphagogic action of histamine, peptone and sinomenine on the thoracic lymph in the cat, the author observed the effects of these substances on the rate of lymph flow from the thoracic duct, protein contents in the lymph and blood sera, blood pressures in the carotid artery, jugular or femoral vein and portal vein, and volumes of the liver and intestines. An attempt was made to find out the difference in the mode of action of lymphagogues in different species by comparing the results of the author's observations on the cat with those on the dog and rabbit reported by other workers. In the majority of cats the thoracic lymph flow was 0.3-0.7 cc/10 min. and the lymph protein content 3-5 per cent, maintaining these conditions persistently for more than five hours with almost no change. By injecting 2 mg/kg histamine into systemic vein the rate of lymph flow reached the maximum of 2-4 times the normal, and the protein in lymph was concentrated. After administration of 300 mg/kg peptone (Witte) or 3 mg/kg sinomenine the lymph flow was accelerated to the similar degree. In the latter two the coagulability of lymph was reduced. Lymphagogic effects of histamine and peptone were reduced when administered into the portal vein, and likewise these effects were diminished after the ligature of periportal lymphatics. However, this latter procedure weakened the effect of sinomenine only slightly. Benadryl inhibited the sinomenine effect markedly. Both the obstruction of portal vein and that of hepatic vein markedly accelerated the lymph flow from the thoracic duct. However, the protein content in lymph was decreased in the case of the former, while on the contrary, it was increased in the case of the latter. The injections of 0.5-1 mg/kg histamine, 500-700 mg/kg peptone and 1-5 mg/kg sinomenine all brought about a triphasic depressor response in the arterial blood pressure. In the majority of cases of histamine there was a transient rise in the portal pressure while in other cases it was decreased. The pressure of jugular vein declined in the case of histamine and rose in the case of peptone, whereas the pressure of femoral vein did not show any definite changes in the case of sinomenine. These substances decreased the volumes of the liver and intestines at the initial stage and turned to increase. A marked tachyphylaxis was recognized in all these actions of sinomenine, but in the actions of the other two drugs it was less marked. From these results, it seems that these three drugs have the effect similar to one another and that the effects of peptone and sinomenine involve histamine release. In all instances the dilatation of capillaries and the increase in the permeability are responsible for the acceleration of the lymph formation, and in the splanchnic area, the intestines, and also the liver seems to be the site of the lymph acceleration. The degree of lymphagogic effects of these drugs in the cat is in between that in the dog and that in the rabbit. This situation may be explained by the fact that the cat does not possess such a well-developed muscular layers of the supra-hepatic vein as possessed by the dog, and the cat is more sensitive to the histamine action of inducing capillary dilatation and permeability increase as compared with the rabbit.