Gene delivery vehicles, known as LPD complexes, prepared from mixing cationic lipid vesicles (L) with cationic peptide (P) and DNA (D) have proven to be very effective at delivering DNA into the nucleus of cells to obtain expresion. Although a considerable amout of work has gone into developing new cationic lipids that improve the level of DNA expression, far less work has investigated the effect of peptide on transfection. The present study aims to determine the structure of LPD complexes as a function of peptide structure. Studies have shown that peptide structure has a significant affect on transfection while electron microscopy studies have shown that as transfection decreases the amount of order seen in the core in the LPD complex increases. Contrast variation SANS will be used to probe the detailed structure of the LPD complex to understand the transfection results.