The present invention provides synthetic immunogenic lipopeptide molecules comprising co-linear T-helper and B cell epitopes, and methods for their production and use in the generation of primary and secondary immune responses, and for the vaccination of animal subjects against particular antigens. More particularly, the present invention provides highly soluble lipopeptides wherein the lipid moiety is attached to the terminal side-chain group of an internal lysine or lysine analog, preferably to the terminal side-chain group of an internal diamino acid residue. Preferably the internal lysine or lysine analog is positioned between the T-helper epitope and the B cell epitope or within the T-helper epitope.