Development of safe and effective technology for delivering functional DNA into cells in an intact organism is crucial to broad applications of gene therapy to human disease. Both viral and nonviral vectors have been developed. Of the technologies currently being studied, liposomal delivery system is particularly attractive. Cationic liposome mediated gene transfection (lipofection), a relatively new technique pioneered by Felgner and coworkers (1), was highly efficient for transfecting cells in culture. The liposomes were composed of an equimolar mixture of a synthetic cationic lipid N-[1-(2,3,-dioleyloxy).