Aspergillus clavatus was not pathogenic to mice when administered intravenously (i.v.); provoked abscesses (i.m.); and granulomata, principally associated with liver and pancreas when given intraperitoneally (i.p.). It was pathogenic for the chicken embryo. In mice given inocula of live or acetone-killed mycelium, granulomata were larger than when conidial suspensions were used. Heated or acetone-killed conidia provoked no host reaction. In mice with granulomata, hepatotoxicity was indicated by cloudy swelling, focal necrosis, and regeneration metaplasia. Tubular degeneration and metaplasia were seen in kidney cortices. Prednisolone treatment of mice, inoculated i.p., resulted in limited mycelial growth in vivo in some animals. Prolonged feeding of inoculated barley caused hair-loss and hyperkeratosis, a lesser incidence resulting from feeding mycelium, and none from feeding conidia. Dry conidia and suspensions introduced by nasal instillation provoked no respiratory pathology. Lung clearance by alveolar ...