Abstract: An inhibition assay for measuring the potency of allergen extracts by incubating a mixture of allergen extract and reference allergen specific IgE in a buffered solution with an insoluble support to which reference allergen is adhered. The conjugated IgE adhering to the insoluble support is reacted with an enzyme labeled anti-IgE antibody and the enzyme label is contacted with a solution of a substrate which will yield a fluorescent product in the presence of the enzyme. The level of fluoresence in the solution is measured. The percentage of inhibition of the allergen specific IgE is determined from fluorescence levels measured for various extract concentrations.