Changes in turbidity of lipid DNA complexes following addition of high concentrations of serum. The selected complexes were prepared at the ratios described in the text in a final volume of 200 μl. The volume was adjusted to 600 μl and the absorbance at 600 nm was determined prior to and after addtion of 400 μl of serum. The absorbance of 40% serum in the absence of lipid and DNA was subtracted as background. The experiment was repeated thrice with similar findings.