Ceramic membranes are classically used for microfiltration of dairy fluids with large wall shear stress values achieved through the use of high crossflow velocities. In this paper, both pilot and laboratory scale studies have been used to investigate the use of polymeric membranes for the production of a casein concentrate from skim milk. Results suggest that very high casein rejections are possible with this approach, but that a low transmembrane pressure is required to facilitate whey protein transmission. As expected, membrane flux increases with both transmembrane pressure and temperature. Permeate composition is essentially independent of temperature, with the notable exception of the K-casein content, which is detected at 50 degrees C but not at 10 degrees C. This leakage of K-casein at the higher temperature may result from damage to the surface of the casein micelles induced by shear forces in the membrane circuit pump. The work has also shown the usefulness of a laboratory crossflow apparatus for such experiments, with results on this unit consistent with those obtained using a full scale spiral wound element. (c) 2007 Elsevier B.V. All rights reserved.