Abstract: A method of discriminating between specific antibodies in samples of sera or other body fluids from humans or other primates containing antibodies arising from infection with HTLV-I, containing antibodies arising from infection with HTLV-II or containing antibodies arising from infection with related retroviruses, is described. In said method, the sample to be analyzed is subjected to at least four immunoassays, each using a different diagnostic antigen selected from four defined groups of peptides. Additionally, an immunoassay kit adapted for said method of discrimination, new peptides and a method of detecting antibodies with said peptides, are described.