The influence of Lorentz forces generated by faradaic currents and magnetic fields from permanent magnets on the momentum and mass transfer in natural convection copper electrolysis is discussed. Flow field measurements and visualizations of the concentration distribution are given and related to measured mean current densities. Flow structure as well as mass transfer depend strongly on the direction of the Lorentz force relative to that of natural convection. (C) 2004 Elsevier Ltd. All rights reserved.