Aspergillosis is a primary respiratory and occasionally generalized infection caused by species of Aspergillus. It is world-wide in distribution and has been recorded in almost all domestic animals and birds as well as many wild species. The disease is characterized by the formation of yellowish caseous nodules or plaques and has been known to affect almost every organ of the body. Diagnosis is by the demonstration of hyphae in the lesions and by the culture of the pathogen. Iodide therapy has been used with some success in human infections, but few animal cases have been diagnosed before death. The removal of the source of the fungus spores appears to be the only satisfactory method of control.Aspergillosis has been recorded in almost every species of domesticated animal and bird and in a great many free-living and captive wild creatures. It was one of the first of the mycoses of animals to be described and helped to focus attention on the microbial causes of disease at a time when bacteria were still microscopical curiosities. From the time of its discovery in a jay by Mayer & Emmert in 1815, until the end of the nineteenth century a great many papers appeared on the disease, including a number of monographic treatments, and as a result, much of our present knowledge of the disease was already known by 1900. Relatively few reports have appeared since that time, but within the past few years renewed interest has led to the confirmation of much of the earlier work and has provided a better understanding of the role of Aspergillus fumigatus and other fungi in respiratory diseases in both man and animals. There is no recent general review of aspergillosis and the outstanding works of Renon (1897) and Lucet (1897) have remained the standard texts for sixty years.