We have studied the structural properties of the triple complex dioleoylphosphatidylcholine-DNA-Mn2+ by means of synchrotron x-ray diffraction. The data revel a novel multilamellar structure similar to that recently found in cationic liposomes-DNA complexes. ne study of the bilayer undulations suggests that condensation of the DNA within the lipid bilayers reduces the flexibility of the lamellae in the complex and suppresses almost completely the undulatory fluctuations. These complexes are of grate interest for potential applications as synthetically-based nonviral carriers of DNA vectors for gene therapy.