Cell membranes are impermeable to most molecules that are not actively imported by living cells, including all macromolecules and even small molecules whose physiochemical properties prevent passive membrane diffusion. However, recently, cell-penetrating peptides (CPPs), short positive charged peptides believed to enter cells by penetrating cell membranes, have attracted great interest in the hope of enhancing gene therapy, vaccine development and drug delivery. They mainly use an endocytic route for internalization. In order to improve the intracellular biodisponibility and bioactivity it is essential to identify novel molecules that use different internalization mechanisms; among these, are peptides derived from viral glycoproteins. We plan to determine the location of these sequences in model membrane systems like liposomes, in particular small unilamellar vescicle (SUV) and large unilamellar vescicle will be prepared with differents lipids contents. In fact, lipidpeptide interactions play a key role in the internalization process and understanding what happens at a molecmolecular level will help in designing novel molecules with increased ability to cross the membrane.