Previously, detailed error analyses have been published only for one of the simplest (graphical) and for one of the most complex (all-numerical) data-evaluation methods of the potentiostatic relaxation technique in the nonlinear current density—overpotential range. The latter extends the range of applicability of the technique to several orders-of-magnitude faster reactions but at the price of extensive computational requirements. There is a need for an intermediate range data-evaluation method for reactions with rates too fast for the classical, graphical method but not fast enough to justify extensive computations. Such an intermediate range data-evaluation method is described and evaluated in this paper. It is based on a computer curve-fitting method using the classical relaxation equation of Gerischer and Vielstich. The limitations of this method are described, and applicability diagrams are presented. For the determination of the exchange current density of an electrode reaction, this intermediate method is limited to one to three orders-of-magnitude slower reactions, as contrasted to the all-numerical data-evaluation method, which consists of coupling a numerical diffusion equation solver routine with the nonlinear multidimensional least-squares curve-fitting program. The reason for this limited applicability is that the classical relaxation equation was derived by using several simplification in the model of the electrode reaction system. The most damaging of these simplifications is the neglect of the effects of the uncompensated solution resistance between the working and reference electrodes. The use of this intermediate applicability data-evaluation method is still justified, when applicable, by an about one order-of-magnitude decreased computational time requirement.