In a recent paper, Gekas et al. (Chem. Engng Sci. 48, 2753-2765) presented a theoretical approach to study the adsorption interplay in protein ultrafiltration. The model is based on transient mass transfer in the boundary layer and introduces as a novelty the kinetics of adsorption on the wall boundary of the membrane, an approach basically different from that of semi-empirical models currently employed. The model used two independent kinetic equations : one for the quantity adsorbed at a given time (C-a) and the other for the additional resistance due to adsorption (R-ad) The aim of this paper is to develop and to improve this model, but keeping Gekas’ valuable new approach. First, a critical review of the model is made, correcting the problem statement but maintaining the two independent kinetic equations formulated. Second, the model has been modified and improved, using a unique kinetic equation for the adsorbed amount of protein, which allows the hydraulic resistance due to the adsorption to be calculated directly. Results obtained with this improved model are compared with those of Gekas et al. The behaviour of fluxes, wall concentration and concentration profiles predicted by the improved model are explained more coherently.