The effects of panaxytrion as known to be a cytotoxic substance isolated from Panax ginseng on the immune responses were examined. The i.p. administration of panaxytriol to normal mice for 6 consecutive days as doses of 5, 10 and 20 mg/kg suppressed the increase of body weight dose-dependently but did not affect the weight ratio of immunoorgans to body weight, No significant changes were observed in the humoral immune responses as measured by Arthus reaction and plaque forming cells and in the cellular immune response as measured by delayed hypersensitivity as well as phagocytic activity of reticuloendotherial system. These results suggested that panaxytriol, a cytotoxic substance to cancer cells, has no detrimental effects on the immune function in normal mice.