This work addresses the mass transfer modelling of ternary solutions, water/lysozyme/sodiurn chloride, in the slit feed channel of a ultrafiltration (UF) cell. Permeation experiments are performed using a laboratory-made UF cellulose acetate membrane, characterised by an hydraulic permeability of 2.05 x 10(-11) m/s/Pa and a molecular weight cut-off of 30 kDa. The simulation of the UF operating conditions with recourse to computer fluid dynamics allows the prediction of the selective permeation performance in terms of permeation fluxes and concentration polarization. The predictions of the permeation fluxes based on different mass transport assumptions are compared with experimental ones and a good agreement is obtained. (c) 2005 Elsevier Ltd. All rights reserved.