Isolates of bovine immunodeficiency virus (BIV) exhibit a striking genomic diversity, most of which are located in the viral envelope gene. Since this property of the BIV group of viruses may play an important role in the pathobiology of the virus, the surface envelope gene, particularly the conserved (C) 2, hypervariable (V) 1, V2 and C3 regions, of eleven different isolates from different environments with different bovine breeds naturally infected with BIV, including dairy cows in Japan, buffaloes in Pakistan and draught animals in Cambodia, were sequenced. When compared to the nucleotide sequence of American BIV isolates, all Asian BIV field isolates seem to be smaller, several base substitutions were observed in the V1 region, and deletions were also found in the V2 region of env gene in these samples. However, deduced amino acid sequences were not so different among isolates from different bovine breeds, suggesting that bovine susceptibility to BIV infection may not depend upon bovine breed or buffaloes. Moreover, phylogenetic analysis revealed that genotypes were distinct between Asian and American BIV isolates and these results also provide an information on the molecular epidemiology of naturally occurring BIV infection in cattle and buffaloes.