The present invention relates to lipid assemblies, compositions, and liposomal delivery systems comprising single chain anionic lipids, and the use thereof in diagnosis and therapy. It involves the use of anionic lysolipids for modifying the surface charge of a cationic lipid composition consisting at least one type of cationic lipid, optionally in combination with one or more neutral lipids and/or one or more anionic lipids.
