Panax ginseng is used in traditional Chinese medicine as a prophylactic, a stimulant, and a treatment for various diseases. In addition, ginseng has been found to enhance the immune system and possess an anti-tumor effect. Ginseng appears to stimulate humoral and cell-mediated immune responses and the subsequent increase in titers of lymphocytes and circulating antibodies. Furthermore, ginseng's cancer-prevention properties seem to be mediated through the increased production of interferons and cytokines, which activate natural killer and cytotoxic T-cells that can served to lyse or inhibit growing tumors. Both clinical and epidemiological studies indicated that Panax ginseng can reduce the incidence of cancer in vivo. These results suggest that ginseng shows antitumor effects as an immunomodulator.