We present a simple theoretical analysis of the DNA-DNA electrostatic interactions within charge-neutral lamellar cationic lipid/ DNA complexes (lipoplexes). Although always repulsive as a function of the DNA-DNA interaxial distance, the calculated electrostatic force shows a deep minimum for each value of lipid composition corresponding to an equilibrium distance of the system. The excellent agreement between the equilibrium distances predicted by the model and that experimentally observed in charge-neutral complexes as revealed by synchrotron X-ray diffraction, shows that the spatial dimensionality of both the lipids and the DNA may not be a crucial point to capture the essence of the DNA-DNA interactions within charge-neutral lipoplexes. (C) 2004 Elsevier B.V. All rights reserved.