The balance of proteins adsorbed at a surface is important in a wide range of situations, e.g. implants, nanoparticles. The accepted model is that rapidly diffusing proteins occupy the surface first and are slowly replaced by larger more strongly adsorbed ones. However, preliminary experiments suggest that the situation is complicated by the length of the exposure to the initial protein. If perdeuterated protein is available neutron reflectometry offers the possibility of studying the whole process with considerable precision. We have done preliminary experiments on the exchange of maltose binding protein (MPB) and have established that the interesting differences occur if the initial protein adsorption is in the 15 min - 2 hour time range. We propose to use INTER to follow the processes occurring on these timescales and to follow the time dependence of the exchange.