Velocity measurements inside the screw channels of a co-rotating, self-wiping, twin-screw extruder were carried out. A laser Doppler anemometer (LDA) system was used to measure tangential and axial velocity components in the translational region of one of the screws of a twin-screw extruder. The velocity measurements were carried out using heavy corn syrup at different screw speeds and for two forwards conveying elements differing in their pitch. It was found that velocity profiles in the translational region were substantially affected by the pitch of the screw element, however, screw speed (30–90 r.p.m.) did not have a significant effect on the shape of the velocity profiles. The range of velocity values in a 14 mm pitch screw element was wider than that in a 28 mm pitch screw element. Experimentally measured velocity profiles were compared with predictions of a one-dimensional model, which showed that the model underpredicted the velocity values, for the 14 mm pitch element.