The effect of antitumor agents (lentinan, PS-K, Mitomycin-C, 6-mercaptopurine, etc.) on the antitumor delayed hypersensitivity reaction (DHR) measured by the foot-pad test was compared with their effect on tumor growth in ddY mice with Ehrlich tumor. These agents all inhibited growth of Ehrlich carcinoma. Lentianan and PS-K enhanced the antitumor DHR, but Mitomycin-C and 6-mercaptopurine did not. By plotting the effect of agents on the anti-tumor DHR against these effects on tumor weight, host-mediated antitumor agents could be differentiated from mitotic poisons. Attempts to distinguish these two types of agents by the same method using a syngeneic tumor system were unsuccessful.