In the present study, the antigenic potential of G009, a polysaccharide isolated from Ganoderma lucidum IY009, was determined in BALB/c mice and Hartley guinea pigs. Antigenicity tests, including passive cutaneous anaphylaxis (PCA), active systemic anaphylaxis (ASA) and indirect hemagglutination test (IHA) were performed according to the established guidelines of National Institute of Safety Research. The results were as follows: 1. Mice showed no production of antibodies against G009 sensitized with an adjuvant, aluminum hydroxide gel (alum), when judged by the heterologous PCA test in rats. Meanwhile, antibodies against ovalbumin (OVA) sensitized with alum were clearly detected. 2. In the studies with guinea pigs, both the sensitization of G009 alone and of G009 with complete Freund`s adjuvant (CFA) did not produce positive reactions in homologous PCA. In the case of ASA, however, G009 alone and G009 with CFA produced positive reactions. 3. No G009 specific reaction was observed in an IHA assay using sera isolated from G009 sensitized mice. These findings suggest that G009 have no antigenicity potential in mice but may have weak antigenicity in guinea pigs.