Under alkaline conditions (pH 12), approximately 90% of the protein was extracted from dehulled yellow mustard flour. The resulting aqueous emulsion was microfiltered using a polysulfone hollow-fiber membrane. A concentration factor of 3 at pH 10 was found to be suitable for microfiltration. A total of 86 % of the protein was recoverable in the form of isolates. Precipitated protein isolate (PPI) from the permeate was essentially free of oil and contained 97% protein (Nx6.25), accounting for 14% of staring protein. PPI from retentate had 20% oil and 71% protein (Nx6.25) (94% oil- and moisture-free basis), representing 64% of the staring protein. Some 8% of proteins were recovered as soluble protein isolates, while approximately 4% of the proteins remained in the meal residue and 7% in the emulsion.