The aim of the proposed study is to elucidate the interaction of the 16 amino acid long peptide "penetratin" with model membranes formed by phospholipid bilayers in order to improve the peptide efficacity and for a better comprehension of the organization of the membrane. The study will be done by depositing the bilayer on a solid substrate (i.e. silicon) by using the Langmuir-Blodgett technique (transfer of monolayers from the air/liquid interface to solid surfaces). Various techniques will be employed and primarily the technique of neutron reflection from which information will be gained on how the lipids reorganize around the peptide and let it pass through without water leakage. Selective deuteration will be possible to resolve the organization of the four components of the system, that is the hydrocarbon chains, the hydrophilic heads, the water molecules adjacent to the heads and the peptides themselves. Similar peptides with either hydrophilic or hydrophobic character will be used. A full comprehension of the system will be achieved by using techniques different and complementary to neutron reflection both available at the ILL and at the collaborating institutions such as ellipsometry, fluorescence microscopy, infra-red surface spectroscopy, near-field microscopy, differential calorimetry.