Rabbits bearing Brown-Pearce tumor in liver or muscle were examined and the following results were obtained. 1. As the growth of the tumor progressed, catalase activity of the liver was remarkably depressed and albumin and α-globulin decreased and β-, γ-globulin and Φ-fraction increased in plasma electrophoresis. 2. Injury of reticuloendothelial system of the liver by x-ray irradiation with 1000r on the liver depressed catalase activity of the liver and decreased albumin and β-, γ-globulin and increased α-globulin in plasma electrophoresis. Transplantability of the tumor and mortality were elevated. 3. Carcinolytic agents played the same role on catalase activity of the liver and plasma protein fraction as x-ray irradiation with 1000r on the liver. They are accounted for a gift to the reticuoloendothelial system of the liver. Carcinolytic effect was not observed in Carcinophylin, Mitomycin and Azan. 4. Activation of reticuloendothelial system of the liver by x-ray irradiation with 60r showed carcinolytic effect and the same pattern as that of natural healing was observed in plasma electrophoresis, but catalase activity of the liver was slightly depressed. 5. In cases of natural healing or intransplantable cases, catalase activity of the liver was elevated and plasma protein fraction showed the change from the pattern of tumor growth to the pattern of its recovering process. γ-globulin increased in early stadium. 6. Immunity inhibited the tumor growth markedly and elevated catalase activity of the liver and showed the same pattern in electrophoresis as the cases of natural healing. 7. γ-globulin is considered to play an important role in carcinolytic process, while it does not show carcinolytic effect by itself.