The reactivity of the antiserum is directed to the Fc subunits of the IgE molecule which represents strict isotype (class) specificity. In immunoelectrophoresis and double radial immunodiffusion, using various antiserum concentrations against appropriate concentrations of IgE, a single precipitin line is obtained which shows a reaction of full identity with the precipitin line obtained with the used immunogen. It does not react with human IgG, including all subclasses, IgA, IgM and IgG/Fab or any non-Ig protein in human serum. As unlabelled secondary antibody for indirect detection of IgE in human cell, tissue substrates and body fluids in immunofluorescence and immunoenzyme assay methods; for the production of immunoconjugates with a selected marker; to prepare insoluble immunoaffinity adsorbents by coupling to an artificial carrier; as catching or detecting antibody reagent in non-isotopic assay methodology (e.g. ELISA) to identify and measure IgE in human serum or other body fluid. When applied in any immunocytochemical or histochemical staining procedure or solid phase coupling technique, the optimum concentration of the IgG preparation should be established.