Velocity measurements were carried out in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder using laser Doppler anemometry. Significantly higher values of axial and tangential velocity components were measured in the nip region, indicating that the fluid accelerated as it moved through the nip. The local volume flow rates in the nip and translational regions were calculated from the measured velocity field. The volume flow rate in the nip was about four times higher than that in the translational region, indicating the positive displacement character of the nip region. The total volume flow rate calculated over the entire cross-section of the extruder was in agreement with the experimentally measured volume flow rate. (C) 2002 Elsevier Science Ltd. All rights reserved.