The adsorption equilibria and kinetics of bovine serum albumin (BSA) and lysozyme to two Cibacron Blue 3GA (CB) modified agarose gels, that is, 6% agarose-coated steel (6AS) and Sepharose CL-6B, in 0.01 kmol . m(-3) tris-HCl buffer (pH 7.5) were studied. Effects of aqueous phase ionic strength on both the adsorption equilibrium and uptake rate of the proteins were significant and distinctly, different between BSA and lysozyme. The adsorption of lysozyme decreased monotonically with increasing ionic strength. Ionic strengths, however, maximized BSA adsorption capacities of the two CB-modified agarose gels in the tris-HCl buffer (about 0.2 kmol . m(-3) for CB-6AS and 0.05 kmol . m(-3) for CB-Sepharose), when the pore-size difference of the two matrixes and electrostatic interactions between the BSA and CB molecules of like charge were considered. The effective diffusivity of BSA, derived from a pore-diffusion model, to both the CB-modified agarose gels increased significantly, with the increasing ionic strength at the ionic strength range of 0.01 to 0.3 kmol . m(-3), due to the electrostatic interactions between the BSA and CB molecules of like charge. In contrast, the effective diffusivities of lysozyme to CB-Sepharose in the buffer containing 0.1 and 0.3 kmol . m(-3) NaCl were nearly the same.