This review focuses on two peptides, MPG and Pep-1, which facilitate the transfer of nucleic acids and proteins, respectively, into subcellular compartments. We have investigated the interactions between these two carrier peptides and model membrane systems as well as the conformational consequences of these interactions. Studies performed with lipid monolayers at the air-water interface have enabled identification of the nature of the lipid-peptide interactions and characterization of the influence of phospholipids on the ability of these peptides to penetrate into lipidic media. Penetration and compression experiments reveal that both peptides interact strongly with phospholipids, and observations on Langmuir-Blodgett transfers indicate that they can modify the lipid organization. Conformational investigations indicate that the lipid-peptide interaction govern the conformational state of the peptides. Based on the ability of both peptides to promote ion permeabilization of both natural and artificial membranes, we propose a model illustrating the translocation process. For MPG it is based on the formation of a beta-barrel pore-like structure while for Pep-1 it is based on association of helices.