A family of sterol-modified glycerophospholipids (SML) have been synthesized in which the sn-1 or sn-2 position is covalently attached to cholesterol and the alternative position contains an aliphatic chain. The liposomes formed by the SML posses a number of significant advantages over the liposomes formed from the corresponding diacyl lipid/cholesterol mixture including greatly enhanced drug retention and stability in the body. The aim of the present study is to determine the molecular architecture of the vesicles formed by PChcPC, the SML containing a C16 chain and compare it with the structure of vesicles prepared by the corresponding diacyl lipid (DPPC) and cholesterol to see how anchoring the cholesterol to the lipid alters the structure of the resultant vesicles. The information provided by these studies will be invaluble in development of SML for use in drug delivery.