A combined sedimentation and membrane filtration process was investigated for recycling cellulase enzymes in the biomass-to-ethanol process. In the first stage, lignocellulose particles longer than approx 50 mum were removed by means of sedimentation in an inclined settler. Microfiltration tvas then utilized to remove the remaining suspended solids. Finally, the soluble cellulase enzymes were recovered by ultrafiltration. The permeate fluxes obtained in microfiltration and ultrafiltration were approx 400 and 80 L/(m(2.)h), respectively. a preliminary economic analysis shows that the cost benefit of enzyme recycling may be as much as 18 cents/gal of ethanol produced, provided that 75% of the enzyme is recycled in active form.