The reactivity of the antiserum is directed to the Fc portion of the subclass IgG2b. It does not react with other subclasses of IgG, IgG/Fab fragments, IgM and IgA or any non-Ig protein in rat serum, as tested by immunoelectrophoresis and double radial immunodiffusion. In precipitating techniques as immunoelectrophoresis and radial immunodiffusion to identify the presence of IgG2b in rat serum and other body fluids or to determine its concentration. To prepare an immunoadsorbent for the purification of rat IgG2b from serum or plasma.