Available for licensing and commercial distribution is a serological test specifically designed to distinguish between antibodies generated in HIV vaccine recipients and those generated in a natural HIV infection. The method is useful in HIV vaccine development and clinical studies as it can readily detect early breakthrough infections in seroconverted vaccine recipients, thus providing the information required to determine vaccine efficacy. The test kit includes diagnostic peptide fragments derived from human immunodeficiency virus-1 (HIV-1). The peptide epitopes are primarily derived from the GAG-p6 and gp41 genes. These epitopes are broadly reactive with early sera from HIV infected individuals, but do not illicit protective antibodies, or immunologic cytotoxicity, and thus can readily be excluded from current and future HIV-1 vaccine candidates.