The human immunodeficiency virus type 1 (HIV-1) can be subtyped on the basis of nucleotide sequence variability. Knowledge of circulating HIV-1 genotypes or subtypes allows understanding of the origin and spread of HIV-1 in different geographical regions, and is required for rational vaccine development. A study was undertaken to determine the predominant HIV-1 subtype in Australia. Part of the HIV-1 envelope gene (including the variable domain, V3) was sequenced directly from DNA extracted from peripheral blood mononuclear cells of 17 HIV-1 seropositive people in Sydney, Australia. Phylogenetic analysis based on nucleotide sequence suggested that all patients (including individual cases acquired in New Zealand, Papua New Guinea and Thailand) were infected with HIV-1 subtype B. Octapeptides from the HIV-1 envelope V3 loop tip indicated variation but included a predominance of the most common subtype B octapeptides HIGPGRAF (4 cases), NIGPGRAF (3 cases) and PIGPGRAF (1 case). These data suggest that subtype B is the major HIV-1 strain in Australia (and probably in New Zealand and Papua New Guinea), although the importation of HIV-1 acquired overseas is likely to lead to the detection and dissemination of other subtypes in Australia.