Different ultrafilters and membranes were tested with ground wood mill circulation water from an integrated pulp and paper mill. Both the CR 200/1 (cross rotational, CR-filter (TM)) and the VSEP (R) L (vibratory shear enhanced processing) laboratory modules and the CR 1000/10 pilot plant module were investigated. In the pilot plant filtration the effects of the rotor speed, volume reduction factor and pressure were tested. According to the measurements, the lower the pressure and the higher the rotational frequency (CR 200/1) or the vibration amplitude (VSEP L), the less fouling occurred. For the CR-modules the best short time fluxes were obtained with PA 50H and Desal JX membranes, and for the VSEP-module with the PA 50H and C 30F membranes. The C 30F, PA 50H and PES 50H membranes were chosen for the pilot plant filtrations. In the pilot tests at the mill it was observed that the hydrophilic C 30F membranes fouled very little and had fluxes close to 400 l/(m(2)h). The more hydrophobic PA 50H and PES 50H membranes were fouled badly, and cleaning only restored flux for a short time. A concentration factor between 10 and 30 did not influence the flux very much, but inside the equipment the membranes handling the highest concentration had a lower flux. Also in the mill site experiments it was shown that the flux should be kept as close to the critical flux as possible and that this could be achieved with a high cross-flow velocity and the lowest pressure possible for the equipment.