The antigenic properties of conidial preparations of Aspergillus fumigatus were compared with mycelial and culture filtrate extracts by use of sera of patients with aspergillosis and hyperimmune rabbit serum. Biologic activities were tested by intracutaneous tests. The immunologic parameters used were: precipitating properties in double-diffusion, IgG binding by ELISA, IgE binding by enzyme inhibition assay, and by enzyme allergosorbent test. It has been demonstrated that the components that are released after disintegration of spores have positive titers in all immunologic assays. The immunologic properties of these spore plasma extracts are comparable with mycelial and/or culture filtrate extracts that are in accordance with the corresponding skin reactivities. Components that are released spontaneously from spores are only weakly positive or negative in the immunologic assays and demonstrate a very low biologic activity.