HistostarTM (Rat) (Immunostaining Reagent, Anti-Rat) is the labeled polymer prepared by combining amino acid polymers with peroxidase and goat anti-Rat Ig which is reduced to Fab’. IgG fraction purified from immunized goat serum is digested to prepare F(ab’)2. Antigen-specific F(ab’) 2 is affinity-purified with the antigen. Solid-phase absorption is carried out with mouse serum protein. Peroxidase-labeled amino acid polymer is conjugated to Fab’ obtained by reducing F(ab’) 2.