The effects of Shosaikoto, one of the Kampo medicines, on macrophage functions were studied in mice. Oral administration of Shosaikoto (1.2 g/kg of body weight) increased the change of the membrane fluidity of macrophages and diminished prostaglandin E2 production. Moreover, macrophages from mice orally given Shosaikoto phagocytized antigen more efficiently than control macrophages, resulting in presentation of much more antigen to lymphocytes. These results suggest that Shosaikoto enhances the immune response through at least two different routes, that is, through eliminating the inhibition of lymphocyte functions by prostaglandin E2 and through presenting antigen more efficiently.