The switching of the resistivity of conducting polymers during oxidation/reduction cycling has been studied by means of high frequency in situ resistance measurements. The dependence of the polymer resistance on the electrical charge passed during the polymerization is related to the different morphology of the obtained thin films. The electrodes, coated with poly(thienylpyrrole) film exhibit fast and reversible switching behaviour and are suggested for applications in fast polymeric switches. Experimental evidence is presented for the influence of the electrolyte anions and cations on the conductivity switching behaviour.