Change of IgG production of feline mononuclear cell(MNC) was evalual vitro. MNC was treated with lipopolysaccharide(LPS) before cortisol administration. tisol induced change of B cell subpopulation with surface IgG and reduced IgG prods against virus. However, before treatment o$ulcorner$ MNC with LPS induced increasement of subpopulation with surface IgG and IgG production against virus. These results impel: diminution of IgG production by cortisol is well again by LPS treatment.