The influence of adsorbent particles on the characteristics of protein solution filtration was studied. Three media, activated carbon suspensions, beta-lactoglobulin solutions, and a mixture of both, were filtered on a 0.2-mum pore alumina membrane. Moreover, the adsorption of protein on microparticles was studied and 1 isotherm was determined. Comparison of permeate fluxes, apparent retention coefficients, and hydraulic resistance values at steady state conditions highlights the existence of adsorbent-protein interactions. Permeability and retention seems to depend on cross-flow velocity. Correlations are proposed to express steady state fluxes versus operating parameters: cross-flow velocity, transmembrane pressure, and adsorbent and protein concentrations.