Preliminary studies suggested that FIV infection is widespread in the domestic cat population of Brazil [9, 12, 40, 52, 61, 64 ] . A published review indicated that subtype E was the only prevalent in Brazil [77] . Nevertheless, all studies indentified B as the only subtype circulating in FIV positive animals in Brazil, [12, 32, 40, 62] . Here an analysis was conducted with 473 bp of sequence encoding 157 amino acids comprising the V3-V4 region of the envelope glycoprotein from different subtypes, including those reported previously from South America (Figure 2 ). In this study we used this region of env in order to permit us to include more samples from South America. For this phylogenetic tree, the GenBank accession numbers, names, country and subtype for the FIV env sequences included were: M25381. It is important to state that all phylogenetic studies carried out in Brazil were performed in the same area, namely the south-east, and that Brazil is a huge country (Figure 1 ). More widespread surveys of Brazilian isolates are required to determine whether a single subtype of FIV predominates in Brazil. In Brazilian domestic cats, FIV infected cats have been observed over a prolonged period. During this time, few clinical signs were observed, although the virus was replicating and inducing changes in the immune system, leading to a progressive decline in immune function and the development later of overt clinical signs [51, 78, Hagiwara and Teixeira, unpublished data]. Previously, Brazilian studies established relationships between FIV infection and Toxoplasma gondii and Mycoplasma haemofelis [37, 39] . Otherwise, no association with disease has been recorded in cases of Brazilian FIV infection. It has been suggested that clade B viruses may be more ancient and relatively host adapted and thus may be less virulent [2, 50, 63] .