Ultrafiltration of pectin and albumin solutions was carried out on two different membranes. For both solutions, tests were performed at different transmembrane pressures, concentrations and velocities. A model combining the serial resistances and concentration polarization models in the steady state and laminar flow regime was proposed and compared with the experimental results. The model takes into account the mass-transfer and the transmembrane pressure along the membrane to determine a possible transition from pressure- to mass-transfer-controlled regime and to estimate the average permeate flux. For the most part of the tests, the observed behaviour of albumin and pectin ultratiltration and measured fluxes were in accordance with the model predictions. (C) 2006 Elsevier B.V. All rights reserved.