An epizootic of feline infectious peritonitis in a captive cheetah population during 1982-1983 served to focus attention on the susceptibility of the cheetah (Acinoyx jubatus) to infectious disease. Subsequent observations based upon seroepidemiological surveys and electron microscopy of fecal material verified that cheetahs were indeed capable of being infected by coronaviruses, which were antigenically related to coronaviruses affecting domestic cats, i.e. feline infectious peritonitis virus/feline enteric coronavirus. Coincident with the apparent increased susceptibility of the cheetah to infectious diseases, were observations that the cheetah was genetically unusual insofar as large amounts of enzyme-encoding loci were monomorphic, and that unrelated cheetahs were capable of accepting allogenic skin grafts. These data provided the basis for a hypothesis that the cheetah, through intensive inbreeding, had become more susceptible to viral infections as a result of genetic homogeneity.