There is a controversial debate if a magnetic field can influence the rate of electron transfer (ET) reactions. In this paper, we report kinetic measurements of the ET rate constants for the redox couples [IrCl6](2-)/[IrCl6](3-), [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-), and [Fe(H2O)(6)](3+)/[Fe(H2O)(6)](2+) in magnetic fields up to I T. To reduce effects arising from magnetically induced mass transport (magnetohydrodynamic effect), disk microelectrodes with a diameter of 50 mu m were used in potentiodynamic (cyclic and linear sweep voltammetry) and in electrochemical impedance spectroscopy experiments. None of the investigated redox couples showed a magnetic field effect on the ET rate constant.