Bovine respiratory syncytial virus (BRSV) causes lower respiratory tract disease in Young cattle. Recently, it was possible to determine the sequence of the G protein gene, which plays a role in the attachment of BRSV particles to the cells, front three distinct Brazilian isolates. The phylogenetic analysis conducted here using those sequences compared to other worldwide distributed isolates of BRSV allow us to allocate Brazilian strains within the Subgroup B, which was no longer found in the world since the 1970s. One of the Brazilian strains has a major Mutation between amino acid residues 173 and 178, within the central hydrophobic conserved region, exactly on the site of two of the four cysteine-noose forming cysteine residues. Homology modeling with the previously determined NMR structure of this protein domain was made to check whether these mutations altered the three-dimensional conformation of this immunodominant region. Possible consequences on the biological effects induced by Such mutation on the G protein are discussed. (c) 2005 Elsevier B.V. All rights reserved.116416713037