We have compared the immunochemical characteristics of culture-filtrate antigens (Ag) from Aspergillus fumigatus extracted in our laboratory with commercially available Ags. A total of 20 different preparations were studied for protein and carbohydrate content, presence of endotoxins, mycotoxins, and hemolytic toxins. These extracts were analyzed by two-dimensional electrophoresis for protein components. The immunogenicity of the preparations was determined by rocket electrophoresis with rabbit anti-A. fumigatus sera and by agar gel diffusion with sera from patients with allergic bronchopulmonary aspergillosis, aspergilloma, and normal control subjects. In order to have dependable immunologic results, the Ags must be sufficiently pure and reproducible. Until such time as pure and standardized Ags are available, the crude Ags used should be characterized to the extent that adequate reproducibility between preparations can be ascertained. The enzyme profile of the Ag preparations provides a fair indication of the quality of antigenic components, and together with other immunochemical parameters, it will be of use in determining the suitability of the extracts in immunodiagnosis. Immunochemical results demonstrate that commercial Ags contain less proteins and carbohydrates and fewer enzymes than the homemade antigens. In addition, fewer patients demonstrated specific precipitins against commercial Ags than with homemade Ags. This study once again confirms the need for pure standardized Ags for studying the immunologic response in patients with Aspergillus-induced diseases. Until such preparations are readily available, partially purified or crude Ags with known immunochemical properties and enzyme profile may be the choice for immunodiagnosis.