The understanding of electrolyte flow (convection) during metal magnetoelectrolysis can help towards a better quantitative understanding of the magnetohydrodynamic (MHD) effect. This paper summarizes numerical simulations of copper electrolysis in cuboid cells with vertical wall electrodes under the influence of homogeneous external magnetic fields. Horizontal counter-rotation in the top and bottom region is found in cuboid cells exposed to vertical magnetic fields as well as in tall cells exposed to electrodenormal magnetic fields. The main reason for this characteristic convection type induced by the Lorentz force is the vertical thickness variation of the concentration boundary layer along anode and cathode due to natural convection which results in an inhomogeneous current density distribution. Then, in both cases, the magnetic field and the corresponding normal component of the current density create a rotational Lorentz force which drives the horizontal counter-rotating flow. (C) 2009 Elsevier Ltd. All rights reserved.