A first class filter function is a mode of pulse voltammetry that removes completely the current response for a reversible charge transfer reaction without modifying the corresponding signal for a slow charge transfer reaction. Therefore, the application of these modes permits study without interferences of the response for an irreversible electron transfer in those cases where reversible processes are also present. In the double potential step technique, the mode defined by the linear combination c(1)I(1) + c(2)I(2), with I-k, (k = 1,2) being the current response for the potential step k at the end of the corresponding pulse and where E-2 is set on the anodic diffusion current plateau, can be easily modulated as a first class filter function if the ratio of the coefficients c(1)/c(2) and the pulse durations are chosen appropriately. This polarization mode has interesting features that allow us to determine the kinetic parameters of the slow charge transfer reaction and, in addition, the curves obtained are well defined peak-shaped waves displaying zero baselines with the analytical advantages that this represents. (C) 2004 Elsevier B.V. All rights reserved.