Culture filtrate antigens derived from a strain of Aspergillus fumigatus were used in diagnosing aspergillosis, such as aspergilloma, allergic bronchopulmonary aspergillosis and tissue invasive aspergillosis, by the Western immunoblot method detecting the serum specific antibodies, immunoglobulin M (IgM) and immunoglobulin G (IgG). These antibodies in the sera from all patients with those types of aspergillosis were thus detected significantly more clearly than in the healthy, normal controls.Double diffusion tests using the same antigens were also performed to compare the efficacy of these two methods. In several cases showing negative in the double diffusion test, these antibodies were found to react with proteins possessing the molecular weight of 20, 35, 50, 65 and 73kDa, while in other cases showing positive in the double diffusion test, the antibodies could not be distinguished from each other. We therefore used the Western blotting method to distinguish them.From the data obtained it was concluded that serologic diagnosis by the detection of IgM and IgG using the immunoblot method plays an important role in strengthening the clinical diagnosis.