Despite numerous advantages, fluidized bed adsorption is limited in commercial applications due to a poor understanding of the relationships between mass transfer, hydrodynamics, and adsorption. To obtain a better understanding of these parameters, we used two commercially available resins to compare the adsorption of lysozyme as a function of bed expansion and bulk-phase viscosity using frontal analysis. Under static conditions adsorption was well represented by a Langmuir isotherm. Dynamic capacities at breakthrough were measured and normalized relative to the equilibrium capacity of each resin to facilitate direct comparison of resin performance under each condition. To quantify the impact of resin characteristics in expanded bed adsorption, we carried out a comparison of mass-transfer effects using a macroporous resin, Streamline SP, and a hyper-diffusive resin, S-HyperD LS. Both resins are designed for fluidized bed adsorption of proteins. In this study the results of frontal analysis showed that breakthrough was due to mass-transfer limitations of the adsorbing particles at expansions of 2 times the settled bed height. At expansions of 3 and 4 times the settled bed height, axial dispersion increased significantly; however mass-transfer limitations were still the dominant mechanistic feature contributing to early breakthrough at reduced dynamic capacity. Adsorption capacity under all conditions in this study was poorer for the macroporous resin than for the hyper-diffusive resin due to intraparticle mass-transfer limitations.