1. An epizootic disease of ferrets with a very high case fatality rate is described. 2. By the use of suitable material the natural disease can be transmitted experimentally. 3. The primary causative agent of the disease is a filterable virus. 4. Secondary invasion by bacteria of the respiratory tract of infected animals frequently occurs. The most important secondary invader is hemolytic streptococcus. 5. There seems to be no immunological relationship between the virus of the ferret disease and the viruses of canine distemper and of human influenza. 6. Histologically the disease is characterized by cytoplasmic and intranuclear inclusion bodies in epithelial cells of many organs. 7. These inclusion bodies are indistinguishable from those occurring in canine distemper.