BACKGROUND: It has been reported that Korean Red Ginseng saponins are effective in increasing the synthesis of serum proteins, cell proliferation, antibody production against sheep red blood cells, and in various cancers. However, immunomodulating activities for allergens have not been reported yet. OBJECTIVE: This study was aimed to find an immuno modulating activity of a single highly purified ginsenosides, Rb1 and Rg1, by using oxazolone-house dust mite (Ox-HDM) as allergen. METHOD: BALB/c mice were immunized subcutaneously with Ox-HDM containing the alum or ginsenosides, Rb1 and Rg1, twice per 2 wks. Allergen-specific antibodies and IgG subclasses were determined from serum recovered by cardiac puncture 2 wks after the second immunization by using ELISA method. Allergen-specific cellular proliferation was quantified from mononuclear cells obtained from immunized spleens. NK cell cytotoxicity was generated by co-culture of splenic mononuclear cells against YAC-1 cells as target cells. Hemolytic activity of Rb1 and Rg1 was determined by an in vitro assay using sheep red blood cells. RESULT: BALB/c mice immunized with Ox-HDM plus Rb1 or Rg1 produced significantly higher titers of antibodies than mice immunized with alum-adsorbed allergen. Rb1 remarkably increased IgG2b subclass but Rg1 increased IgG2a. Allergen-specific proliferative response was more significantly increased with Rb1 than with alum-adsorbed allergen or Rg1. Rb1 reduced IL-4 production and increased IL-10 production more than alum-adsorbed HDM, but did not affect the IFN-gamma and IL-12 production. However, Rg1 showed weak responses in the production of cytokines. Both ginsenosides of high concentration increased the splenic mononuclear cells that were capable of killing YAC-1 cells. Rb1 did not stimulate the production of reaginic antibody (IgE) but Rg1 and alum did. Rb1 and Rg1 did not show any hemolytic activity up to 500microgram/ml. CONCLUSION: The data suggest that the highly purified ginsenosides extracted from Korean Red Ginseng Radix, Rb1, modulates antigen-specific immune responses via IL-10 production, that Rb1 or Rg1 may be an immunosurveillance in NK cytotoxic activity caused by allergen-specific immunotherapy.