The reduction of ClO4- ions in acid media was studied at rhodized electrodes (roughness factor values of about 100-200) by voltammetric and hydrodynamic (impinging jet) methods. The effect of HClO4 concentration and the influence of pH (at a fixed ionic strength) on the shape of the voltammetric curve was investigated and interpreted. The inhibition of the reduction process by adsorbing anions, first of all by Cl- ions produced by reduction, was demonstrated. It has been stated that reliable information concerning the laws governing the reduction process cannot be obtained from voltammetric measurements alone. As an additional tool, a version of the impinging jet technique was used to find a relationship between the potential E of the rhodized electrode and the reduction rate I. A characteristic, almost symmetric, /I/ versus E curve going through a maximum was obtained from the experimental data. Reduction mechanisms were suggested for the interpretation of the experimental results. The reaction rate versus potential curves calculated on the basis of model assumptions were compared with the experimental data.