In this experiment we aim to investigate, using neutron reflectometry in combination with contrast variation, the intermolecular interaction between the nucleic acid, calf thymus DNA monolayer comprised of a mixture of phospholipid(DSPC) with varying amounts of cholesterol at the oil-water interface in the presence of divalent cation. Of particular interest here is the conformational order of the film as function of DNA concentration which will be studied. In particular the effect of membrane rigidity at the oil/water interface has not been resolved to date and is an important aspect of the current project. The information gained in the study will be invaluable in understanding of the structure and transport properties of the cell membrane as well as helping in the development of vehicles to improve the delivery of nucleic acids (i.e. gene).