The aim of the present study is to the determine, using specular neutron reflection (SNR), the structure of layers formed by novel tri-chain cationic lipids in combination with dioleylphosphatidylethanolamine (DOPE) at the air-water interface and compare them with the structure of layers formed by the corresonding di-chain cationic lipids and DOPE. The tri-chain lipids are of particular interest because, when combined with DOPE, they form excellent gene delivery vehicles, far better than those formed by their di-chain counterparts. Recent small angle neutron scattering studies have suggested that the tri-chain lipids and DOPE form bilayers of unusual structure, it is hoped that the SNR experiments will shed more light on the detailed structure of these bilayers and explain why the tri-chain lipids are so efficient at gene delivery.