We are investigating the mechanism of adsorption of complxes formed from oppositely charged polyelectrolyte and surfactant on to hydrophilic and hydrophobic surfaces. After addition of formulation the amount adsorbed increases until steady state is achieved. After steady stae, the bulk is diluted which initiates a second period of adsorption. In the dilution step, the complexes in the bulk coacervate which causes the secondary adsorption. Our main objective is to study the composition of the adsorbed surface layer. This will assist in our modelling of the mechanism of adsorption, particuarly the secondary adsorption. This is due to the fact that the rates of adsorption will be governed by the composition dependent charge state of pre-adsorbed polymer-surfactant layer as well as the charge state of the bulk complexes. Neutron contrast variation will enable the composition to be determined