A kit for the determination of the ability of a peripheral blood mononuclear cell to bind to a polysaccharide herein provided comprises a detection reagent comprising a fluorescence-labeled immunostimulant polysaccharide; and a reference reagent comprising a fluorescence-labeled material of a polysaccharide different from that used in the fluorescence-labeled immunostimulant polysaccharide, and/or an immunostimulant polysaccharide which is not labeled with any fluorescent material and whose polysaccharide moiety is identical to that included in the fluorescence-labeled immunostimulant polysaccharide. The use of this kit would permit the estimation of the polysaccharide-binding ability of a peripheral blood mononuclear cell in a higher precision of estimation.