A polymer-modified electrode (PME) was tested for the examination of the electrode reactivity in presence of an electroactive specie. Ferrocene (Fc) was chosen as redox probe and cyclic voltammetry (CV) was used to investigate the redox activity of the polymer. The polythiophene matrix used can be easily post-functionalized, allowing to investigate the redox behaviour of a surface-tethered ferrocene conducting polymer compare to the redox properties of the film when the ferrocene is free in solution. Results reported show dramatic changes in voltammetric patterns obtained at 'organic electrode' compared to Pt electrode. When Fc was in solution, the current peak ascribed to Fc oxidation at PME increases promptly as the conductivity of the film switch 'ON'. When Fc units were grafted onto the polymer network, the quartz crystal microbalance shows that the Fc oxidation was assisted by the conducting polymer chain.