Surface modification of cationic lipoplexes has been carried out by means of a postgrafting reaction. The original lipoplexes described comprise a cationic lipid, a neutral lipid, poly(ethylene glycol)-cholesterol (with or without a targeting ligand) and DNA. Modifying their surface via a chemical, postgrafting reaction did not alter their size (approximately 100 nm) nor their ability to compact DNA, but did give a reduced zeta potential (approximately 0 mV) to afford surface neutral particles. With the modified lipoplexes nonspecific NIH3T3 cell surface binding in vitro was inhibited. Intravenous injection of the neutralized lipoplexes in mice showed decreased accumulation of the particles in the lung as compared to PEGylated cationic lipoplexes. Tumor targeting was also achieved in vivo by the addition of an RGD-PEG-Cholesterol as a lipid-ligand in the postgrafted lipoplex formulation.