Complexation of phospholipid lipsomes with a cationic polymer, poly(N-ethyl-4-vinylpyridinium bromide) (PEVP), and subsequent interliposomal migration of the adsorbed macromolecules, have been investigated. Liposomes of two different charge types were examined: (a) a liposomal System, with an overall charge near zero, consisting of zwitterionic phosphatidylcholine (egg lecithin, EL) with added doubly anionic phospholipid, cardiolipin (CL2-), and cationic dihexadecyldimethylammonium bromide (HMAB(+)), in a CL (2-)/HMAB(+) charge-to-charge ratio of 1 : 1; (b) an anionic liposomal system composed of an EL/CL2- mixture plus polyoxyethylene monocetyl ether (Brij 58). Both three-component systems were designed specifically to preclude liposomal aggregation upon electrostatic association with the PEVP, a phenomenon that had complicated analysis of data from several two-component liposomes. PEVP macromolecules were found from fluorescence experiments to migrate among the charge-neutral EL/CL2-/HMAB(+) liposomes. In the case of anionic EL/CL2-/Brij liposomes, a combination of fluorescence and laser microelectrophoresis methods showed that PEVP macromolecules travel from liposome to liposome while being electrostatically associated with anionic lipids.