Chloroplast transit peptides are involved in transport of some proteins to different locations of chloroplast and have differential ability to insert into lipid monolayers with a preference for chloroplast lipids. In solution, the peptide structure depends on the environment. The stability and the structure that these peptides may acquire in the interface and the lateral interaction with lipids are unknown. To point this we have studied the surface properties of a 24 residue chloroplast transit peptide (cTP) corresponding to the wheat ribulose-1,5-bisphosphate carboxylase. We have also applied FTIR for peptide structure studies. In aqueous solution and in a membranous environment, built with zwitterionic lipids, cTP is mainly random-coil, but in SDS micelles cTP changes to a-helical conformation. Surface data indicate that monolayers of pure cTP adopts an a-helical conformation perpendicular to the interface. Mixed with zwitterionic lipids, cTP is immiscible at all lipid/peptide proportions keeping its a-helix structure. When cTP is mixed with POPG monolayers for a 3/1 lipid/peptide surface area relation, cTP is miscible with the lipid and the equivalent area and surface potential reflects that the peptide is squeezed out remaining parallel to the interface.