Effects of red ginseng acidic polysaccharides (RGAP) on immune system were studied. The proliferation of spleen cells was induced by RGAP treatment per se. Cotreatment of lipopolysaccharide $(100;{mu}g/ml)$ or concanavalin A $(1;{mu}g/ml)$ with RGAP further stimulated the spleen cell proliferation. BALB/c mice treated with RGAP showed a slight splenic hyperplasia and increased antibody forming cell response to sheep red blood cells. Flow cytometry analysis revealed an influx of macrophages in the mice treated with RGAP.