As a part of our ongoing effort to develop new antineoplastic immunostimulator from natural sources, bioassay-directed fractionationn of polysaccharides from Korean red ginseng was carried out by observing the proliferation of marine spleen cells and the generation of lymphoklne activated killer (LAK) cells. The acidic polysaccharide fractions proliferated spleen cells and generated LAK cells in proportion to their acidity in vitro. The LAK cell which was induced by ginseng showed tumoricidal activity against both NK celt sensitive and insensitive tumor target cells without major histocompatibility (MHC) restriction. Adherent macrophages and CD4+helper T cells were involved in the generation of the LAK cells. The acidic polysaccharide from Korean red ginseng synerglzed with recombinant IL-2 (rIff-2) at lower than 3 U/ml. The optimal doses of the acidic polysaccharide from Korean red ginseng for the proliferation of spleen cells and for the generation of LAK cells were 1 mg/ml and 100 $mu extrm{g}$/ml, respectively; this means that the mechanisms for the both activities may be different from each other.