Among various biochemical and biological activities of tea polyphenols, we believe inhibition of the expression and release of tumor necrosis factor-α (TNF-α) is crucial, since our study with TNF-α-deficient mice has revealed that TNF-α is an essential factor in tumor promotion. We found that EGCG dose-dependently inhibited AP-1 and NF-κB activation in BALB/3T3 cells treated with okadaic acid, resulting in inhibition of TNF-α gene expression. Furthermore, treatment with 0.1% gene expression as well as TNF-α protein level in the lung of TNF-α transgenic mice; and IL-1β and IL-10 gene expression in the lung was also inhibited by treatment with green tea extract, indicating that green tea inhibits both TNF-α and the cytokines induced by TNF-α in organs. We recently found synergistic effects of EGCG and cancer preventive agents such as tamoxifen and sulindac, on cancer preventive activity. Taken together, the results show that green tea is efficacious as a non-toxic cancer preventive for humans.