A diagnostic kit for the detection of anti-HIV-2 antibodies in a body fluid sample comprising a package containing a polypeptide containing no more than 33 amino acid residues and consisting of one of the following amino acid sequences, AIEKYLEDQAQLNAWGCAFRQVCHTTVPWPNAS, AIEKYLEDQAQLNAWCAFRQVC, AVEKYLKDQAQLNAWGCAFRQVC, AIEKYLKDQAQLNSWGCAFRQVC, AIEKYLEDQAQLNAWGCAFRQVC, AWCAFRQVCHTTVPWPNAS, SWGCAFRQVCHTSVPWVNT, AWGCAFRQVCHTTVPWPNAS, and AWGCAFRQVCHITVPWPNAS, or a polypeptide that differs from this sequence by no more than ten percent of the amino acid sequence, wherein said polypeptide has the sequence --CAFRQVC--, displays immunological cross-reactivity with HIV-2 transmembrane envelope glycoprotein-specific antibodies, and fails to display immunological cross-reactivity with HIV-1 transmembrane envelope glycoprotein-specific antibodies.