Objective:To analyse the genetic and phylogenetic characteristics of HIV-1 group O viruses.Materials and methods:Theenvgene, encoding the gp160 glycoprotein, and a partial p24-encodinggaggene fragment of a Cameroonian (CA9) and a Gabonese (VI686) HIV-1 group O virus, isolated from cultured peripheral blood mononuclear cells of symptomatic patients, were sequenced, aligned with other representatives of group O for which the same region has been documented, and genetically and phylogenetically analysed.Results:Phylogenetic analysis of theenvgene (gp160) revealed that CA9, VI686, ANT70, and four Ha strains formed a separate cluster, which was supported by 100% of all bootstrap trees. In addition, these seven isolates were part of the same clade in the p24 phylogeny. VAU and MVP5180 may represent two other subtypes.Conclusion:We have characterized two group O viruses, originating from Cameroon and Gabon, which show a close evolutionary relationship to ANT70 and four Ha strains based on the entireenvgene, suggestive of a first group O subgroup, tentatively named the HIV-1 group OenvANT70 clade or subtype.