Extracts of defatted soybean flour were processed in polymeric spiral wound and tubular ultrafiltration modules to produce soy protein concentrates. Soy flour suspensions displayed low fouling tendencies with either module when operated at pressures of 235 kPa (35 psi) or less. With soy flour suspension of 2% total solids (TS) at 50degreesC, flux with the spiral module showed asymptotic behavior above 235 kPa, reaching a plateau value of 80 liters per square meter per hour (LMH) at a pressure drop of 69 kPa, equivalent to a cross-flow of 1701 per minute. Flux decreased to 55 LMH at 5% TS and to 22 LMH at 17% TS under these operating conditions. With the tubular module processing 5% soy flour, flux became pressure-independent at 385 kPa (55 psi) at cross-flow velocities of 0.5 and 1.5 ms(-1). Asymptotic fluxes at these velocities were 19 and 44 LMH, respectively. However, at 2.5 ms(-1), flux increased with pressure to 85 LMH at 490 kPa (70 psi). The tubular module flux decreased to 55 LMH at 7% TS and to 24 LMH at 21.6% TS. Flux could be modelled with the film theory mass transfer model and the resistance-in-series model. (C) 2004 Elsevier B.V. All rights reserved.