Simultaneous heat and mass transfer in free convection at horizontal cylinder electrodes has been investigated experimentally wing the electrochemical limiting diffusion current technique. The convective flow patterns occurring have been observed using Schlieren photography. The results confirmed the we of a combined Grashof number (GR(m)) to account for thermal and concentration buoyancy effects. Various combinations of electroactive species concentration, cylinder diameter and cylinder surface temperature have been used. Results have been succesfully correlated by the equations Sh = 0.53(GR(m)Sc)1/4, 7 X 10(7) < GR(m)Sc < 4 X 10(9) and Sh = 0.018(GR(m)Sc)2/5, 4 X 10(9) < GR(m)Sc < 10(11).