Radioimmunoassays suitable for detection of antibodies against mixtures of antigens were used to provide quantitative estimation of antibody activity against Aspergillus fumigatus (Af) antigens. Sera from subjects with allergic bronchopulmonary aspergillosis, aspergillomas, and asthma with immediate-type cutaneous reactivity were studied. With 125I IgE and 125I IgG, a solid phase polystyrene tube multilayered type radioimmunoassay detected IgE and IgG antibodies in the same serum samples. With 125I Af, a solid phase polystyrene tube and a double antibody assay detected IgE and IgG antibodies, respectively, in the same serum samples. We conclude that either type of assay may be used for detection of antibody activity and that demonstration of elevated IgE and IgG antibody levels in the same serum may be useful in characterization and differentiation of disease states in which Af is involved.