The invention concerns immunogenic glycopeptides derived from pathogenic microorganisms, useful for vaccination and diagnosis of infections caused by said pathogenic microorganisms (bacteria or fungi), and methods for selecting them and preparing them. Said glycopeptides are selected in the group consisting of: a1) glycopeptides essentially consisting of a glycosylated T epitope, comprising 14 to 25 amino acids, among which at least a neutral amino acid is bound to a di- or to a trisaccharide (glycoside linkage) and at least 15% among said amino acids are proline, one of the proline being located in position -1 to -4, relative to the position of said neutral amino acid, which glycopeptides are: exhibited by a class II MHC molecule, specifically identified by T CD+4 lymphocytes induced by immunization with the native glycopeptide from which they are derived, but are not identified by the T CD+4 lymphocytes induced by immunization with a non-glycosylated peptide of same sequence and capable of inducing a proliferation of said T CD+4 lymphocytes by which they are identified and the secretion of cytokines by said lymphocytes and b1) glycopeptides having a sequence of 15 to 39 amino acids including the sequence of the glycopeptide as defined in a1), excluding the glycopeptide of sequence SEQ ID NO:11.