Interaction of poly(N-ethyl-4-vinylpyridinium bromide) (PEVP) with mixed liquid Liposomes, composed of diphosphatidylglycerol (cardiolipin, CL2-) carrying two anionic phosphodiester headgroups and neutral phosphatidylcholine (PC), was studied. It was shown that integrity of liposomes in complex with PEVP critically depends on the mole fraction of negatively charged CL2- headgroups in the liposomal membrane nu = 2[CL2-]/(2[CL2-] + [PC]). Liposome integrity remains unchanged unless nu exceeds 0.3. At higher CL2- content, PEVP adsorption results in disruption of liposomes and formation of rather strong nonvesicular PEVP-lipid complexes.