Results are presented which strongly suggest that strains of Aspergillus fumigatus are one of the predominant fungi in molded corn silage. The clavine alkaloids, fumigaclavine A, a new alkaloid designated fumigaclavine C, and several tremorgens belonging to the fumitremorgen group were produced by A. fumigatus strains isolated from molded silage. The LD50 of fumigaclavine C was about 150 mg/kg oral dose in day-old cockerels. Calves dosed with crude extracts of A. fumigatus cultures experienced severe diarrhea, irritability, loss of appetite, and postmortem examination showed serous enteritis and evidence of interstitial changes in the lungs; abnormal changes were not found in other tissues. © 1977, American Chemical Society. All rights reserved.