Ultrafiltration of UHT skimmed milk has been carried out using a smooth disk and a disk equipped with 6-mm-high vanes rotating at high angular velocity omega near a circular 50 kD membrane. Permeate turbidity was less than 2 NTU confirming complete casein micelles retention. The addition of vanes to the disk increases the permeate flux by about 56% due to higher fluid core velocity resulting in higher shear rate at the membrane The permeate flux increases as omega(0.9) and remains independent of concentration until a volume reduction ratio (VRR) of 3 at 2000 rpm. The maximum theoretical VRR corresponding to zero flux was 9.6 for a disk with vanes.