In the composition of commercial RuO2-containing resistive pastes there is also a significant amount of other electro-active metal oxides. Thus, when the pastes are used in the manufacture of thick-film electrodes, the electrochemical response is a complex contribution of all the electro-active metal oxides included in the paste composition. This is an attractive complex system whose electrochemical response has been studied and explained using a model based on surface activity changes of the solids involved in the redox processes. The developed model is able to describe the redox potential of the electrode as a function of the pH and explain the presence of certain anionic interferences. (C) 2007 Elsevier B.V. All rights reserved.