To date complexes prepared from vesicles composed of dichain, cationic lipids (L) with negatively charged DNA (D), known as LD complexes have emerged as one of the major non-viral gene delivery vehicles. Despite the wide spread interest in LD complexes as transfection agents, very little is understood as to their mechanism of action. It is widely believed that understanding their mechanism of action and the barriers to transfection they encounter upon administration will enable the development of improved gene delivery agents. Among the barriers to transfection is serum. The stability of gene delivery vehicles in the presence of serum can be regarded as a first approximation to gain an insight into the behaviour of such lipid-based carriers in the body after injection. This proposal aims to study the effect of serum on the detailed nanostructure of gene delivery vehicles using SANS.