Experiments of crossflow microfiltration enhanced with gas sparging were performed through a multi-tubular microfilter using washed and unwashed yeast suspensions, and yeast-bentonite mixture as test solutions. The washed yeast suspension was prepared by diafiltration to remove protein molecules in the solution. The addition of bentonite particles simulated the effect of co-existence of other microparticles on the yeast microfiltration. In the experiment, the effects of the feed concentration, solution pH and composition in the two-phase and single-phase flow filtration were examined in each feed suspension, at different flow rates and transmembrane pressures. The comparison of the permeate fluxes between the washed and unwashed yeast suspensions was made to reveal the effect of protein fouling on microfiltration membranes. Finally, the effect of the additional microparticles (bentonite) on the microtiltration of yeast suspension was studied over different range of feed composition. The experimental results show that (a) gas sparging can significantly increase the permeate flux of yeast microtiltration, (b) the feed pH has a profound effect on the permeate flux of yeast microfiltration, (c) the removal of extracellular substances results in much higher permeate flux (washed yeast) confirming that these were the major foulants and (d) the addition of inert particles can affect the microfiltration permeate flux and adding bentonite particles reduces the permeate flux of yeast microfiltration. (C) 2004 Elsevier B.V. All rights reserved.