The effects of protein adsorption by adsorbents at the membrane permeate side on protein transmission through an ultrafiltration membrane are examined using a pseudo-steady state convection-diffusion model. The permeate side protein concentration gradient formed by the ultrafiltration-cum-adsorption process can enhance the total protein transmission rate considerably at low values of permeate flux. The permeate bulk protein concentration does not affect the enhancement effect much as long as it is relatively lower than the feed bulk concentration; it is most often the case for ultrafiltration-cum-adsorption during the protein loading period in a ultrafiltration-cum-adsorption process. The larger the membrane pore size and the thinner the membrane skin layer, the more significant the enhancement effect due to permeate side protein adsorption in the beads. For binary protein mixtures, the ideal situation will be using an adsorbent which selectively binds only the desired protein and therefore its transmission will be enhanced. In cases where the adsorbent will bind both proteins, transmission of the smaller protein will be enhanced more significantly. (C) 2003 Elsevier B.V. All rights reserved.