AbstractA 15‐residue hybrid peptide (KWKLFKKIGAVLKVL‐amide) incorporating partial sequences of cecropin A and melittin causes the release of carboxyfluoresceine encapsulated in phosphatidylcholine liposomes. Succinylation of the amino groups in the N‐terminus and lysine side chains inhibits the effect of this peptide on liposome permeability. Conformational analysis of the parent peptide and its succinyl derivative by CD and nmr indicates that both peptides form amphipathic α‐helices in the presence of hexafluoro‐2‐propanol, but only the unmodified peptide acquires a relevant level of α‐helical conformation in the presence of liposomes. © 1994 John Wiley & Sons, Inc.