A mathematical model for the hindered diffusion and competitive adsorption of two proteins in an agarose gel has been developed. In a simulation program the model has been used to study the competing and displacement effects on a single bead for lysozyme and bovine serum albumin (BSA) bound to the ligand Cibacron Blue in agarose gel. The model takes into account hindered diffusion described by the Renkin model, competitive Langmuir adsorption kinetics, pore size distribution of the gel, and a shrinking effective pore radius attributed to molecule-to-ligand binding. The simulation model can easily explain displacement of BSA or lysozyme dependent on the binding capacity, kinetics, and diffusion. The influence of a bimodal pore size distribution is demonstrated. It also provides insight into the phenomenon of static vs. dynamic binding capacity observed in experimental determinations of the isotherm. (C) 2004 American Institute of Chemical Engineers.