An application of the antimicrobial peptides (AP) as antibiotics of new generation requires comprehensive studies of the interaction of these peptides with a cell membrane (CM). Despite the big progress in characterization of the AP-CM system, its elastic properties remain unclear. In the present work we present studies of the structure and the bending rigidity of phospholipid monolayers formed at hexadecane/water interface in presence or absence of antimicrobial peptides. It is shown that due to the interactions between the monolayer and the peptide, the bending rigidity decreases after the injection of the peptide. (c) 2006 Elsevier B.V. All rights reserved.