Spontaneous fatal aspergillosis occurred in several species of parrots imported from Latin America, Australia, Malaya and Ghana for studies on the control of psittacosis. Over a period of 4 years, 655 parrots were imported for use in these studies. All birds that died during these investigations were necropsied, and the internal organs of 45 were found to have macroscopic lesions suggestive of aspergillosis. Of these 45 suspected cases, 32 were confirmed as aspergillosis by both histopathology and culture, and three others by histopathology alone. There was no evidence that the remaining 10 had this disease. Of the 32 culturally confirmed cases, 13 were found to be caused by Aspergillus fumigatus, 16 by A. oryzae, and three by both fungi. In this series, three sets of circumstances appear to have been associated with the development of fatal aspergillosis. Their capture and transport to the United States, the administration of chlortetracycline used in the control of psittacosis, and the administration of cortisone acetate in an attempt to activate existent latent psittacosis infections. The possible causal relationship of these factors are discussed.