The basic properties of the electrochemical track etching method proposed by Tommasino were studied for PC and PET foils irradiated with fission fragments and/or alpha-particles. Etching was performed in a specially designed double-wall vessel applying electric fields of different strengths and frequencies. The variation in the diameters of the discharge spots produced around the tracks of fission fragments entering PC and PET foils at right angles was systematically studied as a function of the strength and frequency of the electric field, etching time and etchant temperature. For alpha-tracks registered in PC foils the dependence of the discharge spot diameter on particle energy was also determined. It was found that the production of discharge spots started at a threshold field strength depending on the type of particle. The temperature dependence of the growing rate of discharge spots followed the Arrhenius law, but with a reduced activation energy as compared to that obtained for the chemical etching rate of the bulk material.