Bovine immunodeficiency-like virus (BIV) is a recently characterized bovine lentivirus. This virus has structural, genetic, antigenic as well as biological properties similar to human immunodeficiency virus (HIV). There is very little known about the pathogenesis, the genetic diversity, the host immune response, the epidemiology of BIV infection and whether BIV infection can be detected world-wide. Currently, there is only one isolate that has been fully characterized. The original BIV was isolated in 1972 from a calf with persistent lymphocytosis, and infected animals also developed lymphadenopathy and central nervous system lesions. However, animal experimentally injected with the same BIV strain developed only hyperlymphocytosis and enlargement of peripheral lymph nodes, but no immunodeficiencies were observed. It is possible that this passaged virus has been attenuated and there is a need to isolate and characterize more recent field isolates of BIV. Preliminary results indicate BIV infection can also be found in China. About 3% of the tested animals were found to be seropositive for BIV. The long term objective is to understand the biology of BIV infection, the epidemiology of its infection world-wide, and to use it as a model for studying lentivirus infection. The immediate approaches are to screen a large panel of bovine serum throughout northern China, to determine the frequency of BIV infection in using recombinant BIV proteins that have been expressed in E. coli. and to clone and sequence the genomes of the new isolates. These proposed studies are significant as they will generate valuable information about BIV infection in China, the diversity of bovine lentivirus, and the pathogenesis of BIV infection. Besides helping us to understand BIV as a bovine disease, the information generated from the study will help to evaluate whether BIV can be developed into an animal for studying human lentivirus infection, its mechanism in immunosuppression, and as a model for testing possible antiviral therapy and vaccine.