A peptide (called A-15) composed of 15 amino acids of the gp41 (from position 599 to position 613 of the sequence encoded by the env gene) of HIV-1 has been used as an antigen to search for antibodies in 347 sera of at-risk for HIV-1 infection subjects. The purpose was of comparing the prevalence of these antibodies with that of HIV-1 total EIA antibodies and HIV-1 immunoblotting antibodies. Assuming immunoblotting test as reference test for detecting a HIV-1 infection, the antibodies against peptide A-15 show the same sensitivity and specificity when compared with other HIV-1 total EIA antibodies tests.