Among the molds causing allergy, Aspergillus fumigatus (Af) constituted a major species present both indoors and outdoors. The antigens both secreted and bound to hyphae and conidia have been isolated for immunodiagnosis of allergic aspergillosis. The crude extracts have been used to demonstrate IgE antibody in vitro and for skin testing. The crude extracts contain many antigenic and non-antigenic components and toxins and have demonstrated inconsistent reactivities. In addition, similarity with other allergens also may complicate specific diagnosis. A number of methods including conventional purification and fractionation methods have been used to obtain relevant antigens. In recent years, monoclonal antibody dependent affinity purification and molecular biology methods have obtained considerable progress in the allergen purification and in developing specific and reliable immunoassays. However, international standards are still lacking and hence, comparison of results among laboratories are not possible yet.