Viral DNA sequences were determined over the V3 region of env from 28 infected individuals living in the high mV·l prevalence Brazilian cities of Rio de Janeiro and São Paulo. Twenty-six belonged to envelope sequence subtype B, prevalent in North America and Europe, and one was c1assifiedas subtype F, found recently in Brazil and in Romania (one appeared to be a B/F recombinant). Octameric sequences at the tip of the subtype B V3 loops were variable and distinct from those prevalent in North America and Europe. The GPGR motü, prevalent in North AmericanlEuropean strains, was found in only 8 (28.5%) sequences, whereas GWGR was found in 12 (43%) and novel sequences in 8 (28.5%). Brazilian subtype B sequences also diverged from the consensus North AmericanlEuropean strains over the remainder of the V3loop. These results suggest that Brazilian mv·l B strains may have important antigenic differences from prototype subtype B strains currently being evaluated for use in HIV vaccines. These results should be taken into account for future vaccine programs in Brazil.