Neutron reflectivity measurements were performed on a cell membrane mimic system, developed by Liu et al., consisting of a polyelectrolyte multilayer plus synthetic terpolymer plus a phospholipid layer (PE + TER + PC) assembly, at all of the intermediate steps in the assembly of the composite, to obtain neutron scattering length density depth profiles. (1)The polyelectrolyte multilayer functions as a soft, water-containing "cushion" for the membrane mimic, formed by the synthetic terpolymer and the phospholipid layer. The assemblies were studied dry and in 92% humidity using a phase-sensitive neutron reflectometry technique. By use of two water conditions (D2O and H2O mixtures) on the PE + TER + PC assembly, the distribution of water in the layers was obtained. It was found that under 92% humidity conditions, the supported membrane mimic has 40% water content in the "cushion" polyelectrolyte multilayer and 10% water content in the terpolymer-phospholipid region. The overall thickness change, due to water uptake, was found to be 20Angstrom. Because fusing phospholipid vesicles onto the polyelectrolyte multilayer plus synthetic terpolymer assembly shows an overall 30Angstrom increase in thickness of the composite, it can be inferred that a phospholipid monolayer was formed.