The competitive nature of protein adsorption has been investigated in situ by surface plasmon resonance (SPR) analysis. The adsorption from blood plasma solutions of albumin, fibrinogen and immunoglobulin-G (IgG), to a polystyrene surface was investigated as part of concentration- and time-dependent studies, to observe the sequential adsorption of the three proteins at the surface. Adsorption of plasma solutions at a range of concentrations or incubation times was performed and the resulting surfaces were probed by the addition of an appropriate antibody to the protein surface. The process was repeated for each antigen leading to a surface concentration profile of each protein with respect to plasma concentration and plasma incubation time. The SPR was able to detect changes in the relative surface concentration of each component demonstrating that the protein's residence time at the interface was dependent upon its molecular weight, bulk concentration and surface affinity. All ri,hts reserved