A vibratory shear-enhanced filtration system (VSEP) was used for the separation of casein micelles from whey proteins of skim milk reconstituted from low heat milk powder, which has a similar protein content as fresh milk. This paper compares the performances of microfiltration (MF) with a 0.1 pm pore Teflon membrane and of an ultrafiltration (UF) polyethersulfone-one with 150 kD cut-off. The critical flux for stable operation was investigated in MF by increasing the permeate flux in steps while monitoring the transmembrane pressure. It was found to be 501 h(-1)m(-1) at a volume reduction ratio of 2 and the maximum frequency of 60.75 Hz (tau(w) = 34 Pa). The UF membrane minimizes casein loss in the permeate (turbidity below 20 NTU) with a little reduction in permeate flux. Whey protein transmission in UF was found to be 65-70% for alpha-lactalbumin and 25-30% for P-lactoglobulin.