Five groups of antigens were identified in culture filtrates and extracts from spores and mycelia of Aspergillus clavatus fractionated by gel filtration, affinity chromatography, electrophoresis in polyacrylamide gels and chemical analysis. Some particulate and soluble fractions given by nasal inoculation provoked murine allergic alveolitis in non-sensitized and sensitized precipitin-negative, and sensitized, precipitin-positive, animals. Alveolitis-inducing substances appeared to be glycoprotein precipitinogens, which withstood proteolysis, were preferentially adsorbed by concanavalin A, but which were rendered almost inert by sodium periodate oxidation. Spore walls were particularly rich in allergenic substances extractable by alkaline hydrolysis. Delipidated dead spores provoked more severe disease in all immunological groups of mice than live spores. Polysacchraride extracts and acid hydrolysates of spore walls were unreactive.