Rabbits were exposed to spores of Aspergillus fumigatus by 1 of 2 routes: exposure to aerosols of dry spores or introduction of liquid suspensions of spores directly into the stomach. Rabbits also were exposed to aerosols containing spores of a Penicillium sp. Cultural and microscopic examinations of tissues from the respiratory and gastrointestinal tracts indicated fungi were distributed throughout the gastrointestinal tract of the rabbits within 1 hour after exposure to aerosols of A fumigatus or Penicillum spores. Viable A fumigatus and Penicillium were detected in lung tissues of rabbits for 2 or 3 weeks after inhalation of spores. Aspergillus fumigatus was isolated from the gastrointestinal tract no more than 1 week after aerosol exposure, and Penicillium, not beyond 48 hours. However, when large numbers of A fumigatus spores were introduced directly into the stomach, fungi were isolated from tissues for as long as 16 days after exposure even though the intestinal contents were negative 4 to 7 days after introduction of spores. Tests for precipitating antibody were negative, with one exception, among 26 rabbits surviving for 2 weeks or more. Microscopic changes were more pronounced in rabbits exposed to spores of A fumigatus than in rabbits exposed to Penicillium spores.