Analysis of sera from patients suffering from allergic asthma, extrinsic allergic alveolitis (EAA) due to Aspergillus fumigatus or allergic bronchopulmonary aspergillosis (ABPA) by means of IEF immunoprint and Western blot showed characteristic IgG subclasses and IgE responses. Asthmatic patients revealed specific IgE antibodies. IgG subclass reactivities in asthmatics and healthy blood donors were weak and uncharacteristic. Major allergens recognized by asthmatic patients have isoelectric points (pI) of pI 4.4 and 4.8 and molecular weights of 20, 29, 34, 38 and 45 kD. Patients suffering from EAA typically demonstrated strong IgG subclass reactivities with an emphasis to IgG1 and IgG2, while no specific IgE was found. Various major antigens could be identified. Reaction to a pI 6.0 antigen seemed to be characteristic for EAA. ABPA patients showed strong reactivities of all IgG subclasses and of IgE. An intense IgG4 reaction appeared as a typical marker for ABPA. Several major antigens and allergens could be determined. Especially the IgG4 reactivities to proteins with pI 4.6, 5.0, 5.2, 5.4 and 6.5 and molecular weights of 14, 20, 29, 34, 38 and 45 kD seemed to be a characteristic pattern in ABPA. Furthermore, IgE antibodies to culture filtrate components of 34 and 38 kD appeared to be typical in ABPA.