Transduction efficiency of the selected complexes in mice. 25 μg of DNA was complexed at the ratios of lipid to DNA to protamine sulfate described in the text in a final volume of 300 μl PBS. Threehundred μl of the complexes were injected into the tail vein of 6–8 weeks old Balb C mice. After 24 hours luciferase expression in the lungs was determined and normalised per μg protein extract. Values represent the mean and the standard deviation of five mice per group.