This paper investigates the microfiltration of skim milk in order to separate caseins micelles from two whey proteins, alpha-lactalbumin (alpha-La) and beta-lactoglobulin (beta-Lg), using a modified dynamic filtration pi lot (MSD) consisting in 6 ceramic 9-cm diameter membrane disks of 0.2 mu m pores, rotating around a shaft inside cylindrical housing. A comparison was made with another dynamic filtration module consisting in a disk rotating near a fixed PVDF 15.5 cm diameter membrane with 0.15 mu m pores. Maximum permeate fluxes were 120 L h(-1) m(-2) with the MSD module at 1930 rpm and at 40 degrees C, and 210 L h(-1) m(-2) at 2500 rpm and 45 degrees C, with the rotating disk module. Casein rejection was around 99% at high speed for both membranes. alpha-La transmission decreased with increasing transmembrame pressure (TMP) from 75% to 60% for ceramic membranes and from 25% to 10% for the PVDF one. beta-Lg transmissions were lower, ranging from 23% to 15% for ceramic membranes and from 20% to 5% for the PVDF one. In a concentration test with the PVDF membrane at 2000 rpm, the flux decayed from 200 Lh(-1) m(-2) at initial concentration to 80 L h(-1) m(-2) at VRR = 3.2 and 22.1% of the initial alpha-La mass was recovered in the permeate, against 8.1% for beta-Lg. Permeate fluxes in the mass transfer limited regime (J(lim)) of the MSD and rotating disk module operated at various speeds were well correlated by the equation J(lim) = 17.13 V-av where V-av denoted the disk azimuthal velocity averaged over the membrane area. Measurements of J(lim), taken from Ref. [G. Samuelsson, P. Dejlmek, G. Tragardh, M. Paulsson, Minimizing whey protein retention in crossflow microfiltration of skim milk. Int. Dairy J. 7 (1997) 237-242] during MF of skim milk using tubular ceramic membranes at velocities from 1.5 to 8 m s(-1) with permeate co-current recirculation were found to obey the same correlation. (C) 2008 Elsevier B.V. All rights reserved.