Human immunodeficiency virus and feline immunodeficiency virus are both lentiviruses that cause immunosuppressive disease. Similarities between these diseases have promoted the study of feline immunodeficiency virus as a model for human immunodeficiency virus. Not only have lentiviruses been found in domestic cats but they have been found in nondomestic felids as well. Florida panthers, African lions, and other nondomestic felids have been found to have antibodies directed against lentiviruses and each nondomestic cat has antibodies to a virus that is specific for that species. The phylogenetic relationships of these lentiviruses have been studied and mapped using nucleic acid sequencing technology. Phylogenetic mapping has been an important step for future development of vaccines and antiviral therapy.