Lipopeptides of bacterial origin constitute potent B-lymphocyte and macrophage/monocyte activators in vitro. In vivo they function as immunoadjuvants in parenteral, nasal and oral immunization either in combination or after covalent linkage with antigens. When added to bacterial or viral vaccines, lipopeptides significantly enhance the immune response. This response can be further increased by coupling haplotype specific T_h cell epitopes to the lipopeptides. Lipopeptide-T_h cell epitope-conjugates also constitute immunoadjuvants for the in vitro immunization of either human or mouse B-cells resulting, after fusion with the corresponding myeloma cell lines, in an increased yield of specific antibody secreting hybridomas. The advantages of these novel, chemically well defined lipopeptide-T_h cell epitope-conjugates, besides their ability to induce high atigen-specific titers, is their excellent purity, their lack of toxicity, their stability and their easy and reproducible chemical synthesis in large amounts, Lipopeptide-T_h cell epitope-conjugates are a substitute for Freund`s adjuvant with respect to their efficiency, their lack of side effects and inflammatory reactions.