Mass transfer data have been obtained for copper microelectrodes fixed flush with the surface of a rectangular perspex electrode support firmly fixed in an electrolytic cell. Circular cylindrical promoters were inserted at the bottom of the cell. The electrolyte was equimolal potassium ferricyanide, potassium ferrocyanide and excess sodium hydroxide. The mass transfer data were obtained for the reduction of ferricyanide ion. The mass transfer coefficient increased with increased flow rate of the electrolyte and diameter of the promoter and decreased with increase in spacing between the promoters. (C) 2003 Elsevier Science B.V. All rights reserved.