andchemical treatments are not used (Cheryan 1983).However, one important limitation to the process is thatthe solutes cannot be taken to dryness. Membrane processesare also known to be limited by higher solids. It is not the os-motic pressure of the retained macromolecules, but lowmass transfer rates obtained with concentrated macromole-cules and the high viscosity that makes the pumping of theretentate difficult. Skim milk has been thought to be eco-nomically concentrated to 38% solids (Cheryan 1986).Our objectives were to utilize an ultrafiltration membranesystem and enzymatic treatment as an alternative to acidprecipitation to produce a soy protein isolate or concentratewith reduced phytic acid. The effect of initial solids concen-tration on processing time, flux, permeability, and yield weredetermined. The reproducibility of the ultrafiltration processfor concentrating soy proteins from defatted soy flour