Iron ruthenocyanide films have been prepared using repeated cyclic voltammetry, and the deposition process and the films' electrocatalytic properties in electrolytes containing various cations have been investigated. The cyclic voltammograms recorded the deposition of iron ruthenocyanide (ruthenium purple, or RP) films directly from the mixing of Fe3+ and Ru(CN)(6)(4-) ions from the solutions of six cations: Li+, Na+, K+, Rb+, Cs+, and Tl+. An electrochemical quartz crystal microbalance, cyclic voltammetry, UV-visible spectroscopy, and the stopped-flow method were used to study the growth mechanism of the RP films. The RP films showed a single redox couple with a formal potential that demonstrates a cation effect: Li+, Na+, K+, Rb+, Cs+, and Tl+. The electrochemical and electrochemical quartz crystal microbalance properties of the films indicate that the redox process was confined to the immobilized RP. The electrocatalytic reduction properties of NO2- by the RP films were determined and shown to have a pH dependence. The electrocatalytic oxidation properties of dopamine were also determined. The electrocatalytic reactions of the RP films were investigated using the rotating ring-disk electrode method. (C) 2003 The Electrochemical Society.