Five specific pathogen free cats were inoculated with feline immunodeficiency virus (FIV) isolated in Japan to observe changes toward development of acquired immunodeficiency syndrome (AIDS)-like disease. All inoculated cats had lymphadenopathy and mild respiratory disease shortly after inoculation. Following the initial acute phase lasting for more than 40 weeks, the clinical signs gradually diminished in three animals, and the asymptomatic carrier (AC) stage was observed at 45 (1 cat) and 70 (2 cats) weeks postinoculation (p.i.). Two of the three cats developed respiratory signs and diarrhea at 105 or 106 weeks p.i. One cat died at 121 weeks p.i. with severe wasting, with necropsy findings consistent with AIDS-related complex (ARC). The others were surviving at 150 weeks p.i. with mild clinical signs or asymptomatic. Another group of two cats developed more severe illness without the AC phase. One died at 48 weeks p.i. with the ARC illness. The other cat developed marked emaciation with diarrhea at 75 weeks p.i., and died at 100 weeks p.i. with a histologic diagnosis suggestive of terminal immunodeficiency. Histologically, the lymph nodes showed serial changes toward the terminal illness, from follicular hyperplasia at the acute phase to the lymphoid depletion at the ARC and AIDS-like terminal stages. The FIV antigen was demonstrated in the lymph nodes. The virus was isolated from peripheral blood mononuclear cells of all the inoculated animals. These data demonstrated possible etiologic association of FIV with development of AIDS-like disorders in the cat.