Activities of various kinds of hydrolytic and oxydative enzymes in the Ehrlich solid carcinoma and NF sarcoma were histochemically examined. And the influences of the antitumor agents, i.e. Colchicine, Nitromin, Mitomicin C, Endoxan and Merphyrin on these tumor tissues were also observed, and the following results were obtained. 1. The hydrolytic enzymes: The activities of alkaline-phosphatase and acid-phosphatase in both tumors were negative. The activities of β-Esterase and β-glucuronidase were slightly positive in the proliferating area of tissue, while their activities increased in the degenerated area. Aminopeptidase showed stronger activity in the NF sarcoma than in the Ehrlich solid carcinoma, but its activity decreased promptly if the tumor cells degenerated. 2. The oxydative enzymes: Succinic, lactic and α-glycero-phosphate dehydrogenase showed moderate activities in the proliferating area of tissue, while their activities decreased, gradually in the area of necrobiosis or necrosis. The activities of malic, glutamic and β-hydroxybutyric dehydrogenase were slightly positive in the proliferating area of tissue, and they increased at the transitional part between the proliferating and necrobiosis area. The activity of glucose-6-phosphate dehydrogenase was negative in the NF sarcoma, but moderately positive in the proliferating area of Ehrlich solid carcinoma. When the tumor cells degenerated, its activity was promptly decreased. 3. The degeneration and necrosis of the tumor cell were observed in various degree by the administration of the antitumor agents. The enzyme activities did not show the special changes by the administration of the antitumor agents. The giant cells were observed in the administration of Endoxan, Nitromin and Merphyrin. The giant cells showed the highly increased activities in β-glucuronidase and all oxydative enzymes.