Complexes prepared from cationic, dichain lipid (L) vesicles, positively chargely targeting peptides (P) and negatively charged DNA (D) or siRNA (R), known as LPDs and LPRs respectively have emerged as major non-viral gene delivery vehicles. Despite the wide spread interest in such complexes as delivery vehicles, little is known about the kinetics of their formation. The present study proposes to use stopped flow SANS measurements in combination with contrast variation to probe the mechanism of formation of the LPD and LPR complexes. An understanding of the mechanisms behind the DNA¿cationic vesicle complex formation event will allow the production of more homogeneous, efficient delivery systems in a pharmaceutically acceptable form.