Many proteins exhibit a lag in lowering the surface tension at the air-water interface. The origin of this lag is not well understood either experimentally or theoretically. The best current model is a mix of diffusion control and inter- and intra-molecular structural changes. Simultaneous neutron reflectometry and surface tensiometry offer a new means for resolving these issues. However, we have also observed that the lag time can be dramatically changed in mixtures of proteins and we believe that the study of such changes will give an even more sensitive means for understanding the behaviour of protein adsorption at the air water interface.