The motion of mono-sized 3 mm glass beads in a V-mixer was studied using the Positron Emission Particle Tracking (PEPT) technique. A similarity is found between the motion in V-mixers and in rotating drums. In both cases, there is a surface flow regime and a solid body motion regime. Within each arm of the mixer, there is a regular circulation in rotating Lagrangian coordinates, the direction of which changes as the volumetric fill increases. The flow reversal occurs at intermediate fills and is system dependent. It was attributed to the surface flow regime and the freeboard in the arm of the V-mixer. The circulation intensity in the arm was quantified and was found to increase quadratically with increasing rotational speed. It was attributed to the kinetic energies of particles within each arm. The circulation intensity decreases when the fill level increases from 10% fill to 46% fill and a minimum value exists at intermediate fills. The axial dispersion coefficient of the particles in the V-mixer increases linearly as the rotational speed increases from 15 rpm to 60 rpm. (c) 2005 Elsevier B.V. All rights reserved.