Résumé : A protein sequence of the viral envelope is responsible for the fusion of the viral membrane with the cell membrane. It has been hypothesized that this fusion protein acts by inserting its hydrophobic moiety into the target membrane. The paper reports on the mode of insertion of the Newcastle disease virus (NDV) fusion protein N-terminus peptide into a lipid membrane using infrared spectroscopy and conformational analysis. The peptide was shown to adopt an oblique orientation with respect to the lipid acyl chains. This unusual orientation is expected to induce the disorganization of the surrounding lipids, which had been suggested as one of the initial events in the virus/cell fusion.