Standard electrode reaction rates for the one-electron reduction of Eu(CF3SO3)(3) on mercury have been measured in various concentrations of the supporting electrolyte tetrabutylammonium perchlorate in N,N-dimethylformamide. The data were obtained from a.c. polarography on the dropping and the hanging mercury electrode in a three-electrode system as well as from cyclic voltammetry in a two-electrode system. The data from cyclic voltammetry were introduced into a numerical simulation program to separate the resistance contribution from the kinetic part of the peak separation. The good agreement found between the standard reaction rate constants from a.c. polarography and the data from cyclic voltammetry prove that cyclic voltammetry in a two-electrode system combined with simulation is a suitable technique for measuring standard reaction rate constants in two-electrode systems. The decrease in the standard electrode reaction rates with increasing supporting electrolyte concentrations was accounted for by the influence of the phi(2) potential and by ion-pair formation.