A new retrovirus was recently discovered in cats affected with an immunodeficiency syndrome (AIDS). The virus shows morphological and biological similarities with the human immunodeficiency virus (HIV), which causes AIDS in human individuals. As the T-lymphocyte is the primary target of the virus, it is termed Feline T-Lymphotropic Lentivirus (FTLV). FTLV is not antigenically related to HIV. Transmission of the virus from animals to human subjects has not been recorded. Cats infected with this virus showed lymphadenopathy, leukopenia, anorexia, chronic stomatitis/gingivitis and other opportunistic forms of infection. Neurological symptoms were also observed. Research is focused on diagnosis, treatment and prevention. Results obtained may contribute to research on AIDS in human subjects.