Tocotrienols were evaluated for activity against transplantable murine tumors inoculated i.p. into mouse, and the activities of two tocotrienols and α-tocopherols were compared. When the compounds were injected i.p., α- and γ-tocotrienols were effective against sarcoma 180, Ehrlich carcinoma, and IMC carcinoma, and γ-tocotrienol showed a slight life-prolonging effect in mice with Meth A fibrosarcoma, but the tocotrienols had no antitumor activity against P388 leukemia at doses of 5-40 mg/kg/d. On the other hand α-tocopherol had only a slight effect against sarcoma 180 and IMC carcinoma. The antitumor activity of γ-tocotrienol was higher than that of α-tocotrienol. Tocotrienols showed growth inhibition of human and mouse tumor cells when the cells were exposed to these agents for 72h in vitro, whereas tocopherol did not show any marked cytotoxic activity. Alpha- and γ-tocotrienols had inhibitory effects on lipid peroxidation of murine microsomes by adriamycin.