The heterogeneous electron transfer rate constant for Fe(CN)(6)(4-/3-) redox system was measured with platinum standard-size and ultramicroelectrodes in NaCl solutions using fast cyclic voltammetry, steady-state voltammetry and FFT-square wave voltammetry. A k(s) of about 0.1 cm s(-1) was obtained with a Pt (0.2 mm radius) electrode. At a standard-size electrode, the electron transfer is also strongly inhibited by the reactant decomposition products. A significant increase in the standard rate constant up to 0.2 cm s(-1) was observed with ultramicroelectrodes. Additionally, the effect of partial blocking of electrode surface by the ferro- and ferricyanide ion decomposition products is significantly reduced at platinum ultramicroelectrodes.