The effects of in-phase oscillation of the retentate and filtrate in crossflow filtration at low Reynolds number are investigated experimentally. Two flat membranes with mean pore size of 0.2 mu m and a filter plate with pore size of 40 mu m were used for the study. The experiments were performed with polymethylmethacrylate (PMMA) suspension and baker's yeast (Saccharomyces cerevisiae) suspension. The solid volume fraction of the suspensions was phi(s) = 0.01. Reynolds number in the laminar range of 0 < Re < 300 was studied. The height of the non-oscillating crossflow velocity v is 0.02 m/s. The frequency f of the oscillation is in the range of 10 Hz < f < 50 Hz and the amplitude A = 0.43 mm. This yields oscillating velocity in the range of 0.06 m/s <= v(osc) <= 0.10 m/s. The transmembrane pressure lies between 1.0 and 20 kPa was applied. The resulting flow was visualized using a CCD camera. The transmembrane flux due to the superimposed oscillations is significantly higher than the flux from conventional crossflow filtration. Manipulation of both the retentate and filtrate/permeate yields constant flux with time. Flux enhancement between 125% and 320% was obtained. The particle deposition on the surface of the filter materials is significantly reduced by the imposed oscillation. With the in-phase oscillation of both retentate and permeate, uniform transmembrane pressure is possible. In general, the flow reversal leads to reduction of membrane fouling and concentration polarization resistance. The calculated friction power input due to applied oscillation is comparatively low. (C) 2009 Elsevier B.V. All rights reserved.