The formation of protein layers on surfaces is important for medical implants and for the consequences of the ingestion of nanoparticles. In the body, a surface is exposed to a cocktail of proteins which changes with time and place. Small proteins adsorb initially and are gradually displaced by larger more strongly adsorbed proteins. We have previously studied heterogeneous exchange of proteins (different proteins) at the solid/liquid interface where both were protonated but the real potential for applying neutron reflectometry is when one of them is deuterated. We have used deuteration to study self exchange of MBP following timed initial exposures of the surface to one of the isotopes and shown a pronounced dependence of the exchange on the length of this initial exposure. We now propose to use labelled proteins to investigate hetergeneous exchange (HSA following MBP exposure).