The literature data and the most important factors relevant to the reduction of perchloric acid at Rh electrodes (smooth polycrystalline, single-crystal faces and rhodized systems) are surveyed. The consequences of model assumptions are analysed for rhodized electrodes. The central role of some adsorption processes was demonstrated using a combined voltammetric and impinging jet method. The experimental results obtained confirm the assumption that the reduction process, which involves several consecutive steps, takes place exclusively on the surface of the electrode and Cl- ions are the main products. The latter species are responsible for the well-known self-inhibition phenomena.