The diagnosis of allergic diseases is commonly carried out by using poorly standardized preparations containing allergenic and non-allergenic components. Recently, monoclonal antibody technology has been applied to the biochemical characterization and to the purification of allergens, in order to evaluate their potential role in the standardization of diagnostic and therapeutic extracts. Three main results have been achieved: 1) the characterization of allergenic epitopes recognized by IgE and IgG from patients' sera; 2) the purification by affinity chromatography of relevant allergenic components; 3) the development of immunoassays for the quantitation of allergens in the commercially available extracts used for diagnosis and therapy.