A peptide corresponding to the N-terminal region of the S protein of hepatitis B virus (Met-Glu-Asn-Ile-Thr-Ser-Gly-Phe-Leu-Gly-Pro-Leu-Leu-Val-Leu-Gln) has been previously demonstrated to perform aggregation and destabilization of acidic liposome bilayers and to adopt a highly stable beta-sheet conformation in the presence of phospholipids. The changes in the lipid moiety produced by this peptide have been followed by fluorescence depolarization and electron microscopy. The later was employed to determine the size and shape of the peptide-vesicle complexes, showing the presence of highly aggregated and fused structures only when negatively charged liposomes were employed. 1,6-Diphenyl-1,3,5-hexatriene depolarization measurements showed that the interaction of the peptide with both negatively charged and zwitterionic liposomes was accompanied by a substantial reduction of the transition amplitude without affecting the temperature of the gel-to-liquid crystalline phase transition. These data are indicative of the peptide insertion inside the bilayer of both types of liposomes affecting the acyl chain order, though only the interaction with acidic phospholipids leads to aggregation and fusion. This preferential destabilization of the peptide towards negatively charged phospholipids can be ascribed to the electrostatic interactions between the peptide and the polar head groups, as monitored by 1-(4-(trimethylammoniumphenyl)-6-phenyl-1,3, 5-hexatriene fluorescence depolarization analysis.