We describe an efficient, nonviral gene transfer system that employs polyethylenimine (PEI 800, 25, 22 kDa), and 1,2-dioleoyl-3-(trimethylammonium) propane (DOTAP) and cholesterol (Chop as lipids (lipopolyplex), at three different lipid/DNA molar ratios (2/1, 5/1, and 17/1), employing five different formulation strategies. PEIs of 800, 25, and 22 kDa are highly effective in condensing plasmid DNA, leading to a complete condensation at N/P (+/-) ratios above 4. Increasing the molar ratio lipid/DNA in the complex results in higher positive values of the zeta potential, while the particle size increases in some protocols, but not in others. PEI of molecular weight 800 kDa used in the formulation of lipopolyplexes results in bigger particles compared to that obtained with the smaller PEI species. Transfection activity is measured using pCMVLuc expressing luciferase is maximal by using strategies 3 and 4 and an N/P molar ratio of 17/1. These complexes have a high efficiency of gene delivery to liver cancer cells, even in the presence of a high serum concentration. Complexes formed with linear PEI are more effective than lipopolyplexes containing branched PEI. The ternary complexes are much more efficient than conventional lipoplexes (cationic lipid and DNA) and polyplexes (cationic polymer and DNA). The same behavior is observed for complexes prepared with the therapeutic gene pCMVIL-12 expressing interleukin-12.