We have recently developed novel ternary lipopolyplex vectors (i.e. gene delivery vectors containing cationic lipid, plasmid DNA and a cationic peptide) in which, for the first time, a trichain cationic lipid has used. The transfection efficiency obtained for these novel lipopolyplexes in a range of cell types is very high and therefore the complexes are under investigation as potential gene delivery vectors. Previous work by our group (Kudsiova et al (2010) Molecular Biosystems. DOI:10.1039/C0MB00149J) has shown a strong relationship between the detailed molecular architecture of a gene delivery complex and its ability to transfect cells. The aim of the proposal is therefore to use SANS in combination with contrast variation to determine the internal structure of the novel, trichain-containing lipopolyplexes in order to understand why they exhibit a high ability to transfect cells.