In South America, natural products with unknown drug effects are used as folk remedies and forpreventive medicine. Among South American natural products, we directed our attention to Propolis,which have been known as medicinal plants, and examined the mechanisms by which these substancesaffect antioxidant activity, anti-tumor activity and immunoresponse. When the antioxidant activities ofPropolis were examined by the DPPH and Rhoudan iron methods, since Propolis contains high levels offlavonoids, it is thought that flavonoids may be responsible for the antioxidant activity in this study. In theexamination of immunoenhancement activity, we measured lymphocyte versus polymorphonuclearleukocyte ratios (L/P activity). The number of lymphocytes was significantly increased in groups treatedwith Proplolis. Specifically, slightly high levels of IFN-γ were measured in mice bearing the S-180carcinoma, after administration of Propolis. This strongly suggests that cellular immunity is especiallyactivated by treatment with Propolis, because production of IFN-α is limited to the T cells and NK cellsstimulated by mitogen and sensitized antigen. TNF-α shows a different extent and mechanism of actiondepending on the target cells. When TNF-α was measured in mice bearing the S-180 carcinoma, micetreated with Propolis showed slightly higher TNF-α levels as compared to the control group. This suggeststhat activated macrophages produce TNF-α in mice treated with Propolis, since activated macrophagesand lymphocytes are the source of most TNF-α. When anti-tumor action was examined using two kindsof sarcoma (Ehrlich solid carcinoma and Sarcoma-180 carcinoma), tumor-suppressive ratios aftertreatment with Propolis was 29.1%. When Sarcoma-180 solid carcinoma was used, tumor-suppressiveratios were 62%. Thus, Propolis showed strong anti-tumor activity against two kinds of solid carcinoma.Taken altogether, this strongly suggests that Propolis enhances original functions of macrophages and NKcells, and as a result, secondarily enhances the immune reaction and suppresses tumor growth.