The influence of an external magnetic field B on the electrochemical behaviour of the systems Cu2+/Cu, Ni2+ /Ni, and [IrCl6](2-)/[IrCl6](3-) has been studied. In the case of Cu depositions in an electrochemical cell with a large ratio of the electrode area and the cell volume the increase of the limiting current density with B can be explained with the interplay of natural convection and the Lorentz force acting on the resulting flow profile (magneto hydrodynamic or MHD effect). Ni depositions also show an MHD effect as well as a tendency to form more fine grained material in the presence of a magnetic field. The results on the homogeneous redox system [IrCl6](2-)/[IrCl6](3-) at 50 mum diameter micro electrodes are in qualitative agreement with recently proposed relationships to describe the influence of a B field on the limiting current density. (C) 2003 Elsevier Ltd. All rights reserved.