Abstract: Horse radish peroxidase (HRP) is treated with phenyl isothiocyanate (PITC) to block the free amino groups on the enzyme. The PITC derivative of HRP is treated with periodate to oxidize the carbohydrate moiety on the enzyme, thus generating aldehyde groups. Gamma G globulin fraction (IgG) purified from an anti-human IgE serum is conjugated to the peroxidase-aldehyde by formation of a Schiff's base between the aldehyde group on the enzyme and the amino groups on the IgG. The Schiff's base is stabilized by reduction using the optimal amounts of sodium borohydride determined by tiration. A stable HRP-anti IgE IgG conjugate prepared thus is employed in a solid phase enzyme immunoassay for the detection of allergen specific IgE. The results of this assay can be used to determine a safe initial hypersensitization dosage level.