When nuclear fraction prepared from Rhodamine sarcoma (sarcoma nuclear fraction) was injected into mice three times every 24 hr, the catalase activity of the liver decreased to one-third of the original activity. 2) By the injection of sarcoma nuclear fraction into mice, the catalase activity with the soluble fraction from homogenates of the liver decreased more significantly than that with the particulate fraction from them. 3) Immunological titration proved that the decrease of catalase activity in the liver of mice injected with sarcoma nuclear fraction was brought about by decrease in the amount of catalase protein. 4) In the mice, whose liver catalase activity had been irreversibly inhibited by injection of 3-amino-1,2,4-triazole, the initial rate for the restoration of the liver catalase activity was significantly showed by further injection of sarcoma nuclear fraction. 5) When the inhibitor of catalase biosynthesis, allylisopropylacetamide, was injected into mice, the activity level of the liver catalase decreased. The extent of decrease by the injection of the inhibitor was slightly lower than that by the injection with sarcoma nuclear fraction, which was almost the same as the extent of decrease by the injection of sarcoma nuclear fraction plus allylisopropylacetamide. 6) It is conceivable that the catalase biosynthesis in the liver was inhibited by the injection of sarcoma nuclear fraction in almost the same manner as by the injection of allylisopropylacetamide. However, it is not certain whether the degradation of liver catalase was slightly stimulated by the injection of sarcoma nuclear fraction.
