New isolated polypeptides of the protein p17 of HIV are described, represented by the formula: NH.sub.2-X.sup.1-Gly-X.sup.2-X.sup.3-Leu-Asp-X.sup.4-Trp-Glu-X.sup.5-Ile-- X.sup.6-Leu-Arg-COOH (SEQ ID NO:1) in which X.sup.1 is an amino acid residue selected from Ser and Arg; X.sup.2 is an amino acid residue selected from Gly, Glu and Ser; X.sup.3 is an amino acid residue selected from Glu, Lys, Asp and Arg; X.sup.4 is an amino acid residue selected from Arg, Ala, Lys, Thr, Ser, Glu, Asp and Gln; X.sup.5 is an amino acid residue selected from Lys, Arg and Ser; and X.sup.6 is an amino acid residue selected from Arg and Gln. These polypeptides, when administered to a subject, are able to evoke anti-p17 neutralizing antibodies and are therefore useful as vaccine or inoculum. Monoclonal and polycolonal anti-p17 antibodies which are able to neutralize the biological activity of this viral protein and to recognize its neutralization epitope in a specific manner are also described.