AbstractThe antitumor effects of vitamin A and its related substances, vitamin E, vitamin K,ß‐carotene, ubiquinone, phytol, and sgualene, were examined using a syngeneic murine tumor system. Intraperitoneal administration of these substances (0.19μmol/mouse/day) slightly suppressed the growth of Meth A fibrosarcoma cells inoculated s.c. into Balb/c mice. Administration of all test substances exceptß‐carotene significantly suppressed the growth of Meth A fibrosarcoma cells rechallenged in Meth A‐primed mice on day 10, but did not influence the growth of Meth 1 fibrosarcoma cells (another syngeneic tumor of Balb/c origin) rechallenged in Meth A‐primed mice on day 10. The growth of Meth A tumor cells was suppressed when Meth A was inoculated together with lymph node cells obtained from the Meth A‐primed Balb/c mice treated with vitamin A, vitamin E, phytol, or squalene. Our findings suggest that certain constituents in green‐yellow vegetables may contribute to the prevention of cancer by augmenting an immunological response against tumor cells in the early stages of carcinogenesis.