The effect of Korean red-ginseng extract on the proliferation and cellular activity of mouse B and T lymphocytes was examined in vitro. Both water and ethanol extract from red-ginseng increased the growth of normal B and T lymphocytes 1.5∼2.5-folds. Saponin and polysaccharide fractions from ginseng extract also stimulated the proliferation of normal lymphocytes much higher than several well-known immunostimulators. B and T lymphoma cell lines responded to the ginseng extract and fractions by growth, too, while non-lymphoid cell lines did not. Immunoglobulin production of unprimed B-lymphocytes was little affected by the ginseng extract and fractions, though the ethanol extract slightly enhanced Ini, production of B-lymphocytes. When cytolytic activity of T lymphocytes against tumor tells was induced in vitro, both of the saponin and polysaccharide fractions and the ginseng ethanol extract increased the cellular activity of cytotoxic T lymphocytes 4-5-folds, while the ginseng water extract did not. Especially, the saponin fraction exhibited 10-times higher stimulatory effect on the cytolytlc activity of cytotoxic T cells than the ethanol extract and the pclysaccharide fraction did. These results suggest that Korean red-ginseng contain potent immunomodulating components to stimulate the proliferation of B and T lymphocytes and the cellular activity of cytotoxic T lymphocytes.