Patients with the Aspergillus-induced diseases allergic bronchopulmonary aspergillosis (ABPA), aspergilloma (fungus ball), and Aspergillus skin test-positive asthma were differentiated immunologically by radioimmunoassay based on their total immunoglobulin E (IgE) and Aspergillus fumigatus-specific IgE levels. In this study, a new, highly sensitive biotin-avidin-linked immunosorbent assay was used to evaluate A. fumigatus-specific antibodies of all immunoglobulin classes. Studied populations included 13 patients with ABPA, 12 with aspergilloma, 9 with Aspergillus skin test-positive asthma, and 9 normal individuals without asthma. A. fumigatus-specific antibodies of all classes were elevated in patients with ABPA, variably elevated in those with aspergilloma, and lowest in the other two groups. This assay demonstrated significantly higher specific IgE antibody levels in the ABPA group over those of the other groups, even with 1:1,000 dilutions of the sera. This study demonstrated that ABPA is a disease characterized by a polyclonal antibody response to Aspergillus antigen and not just a response to IgE and IgG antibody classes. The measurement of other antibody classes, particularly IgD and IgA, could enhance the immunodiagnosis of ABPA. The biotin-avidin-linked immunosorbent assay was found to be a highly sensitive assay that can be a clinically useful alternative to radioimmunoassay in the measurement of A. fumigatus-specific antibodies.