Polypyrrole polystyrene sulfonate resins have been electrochemically synthesized, and the ability of these films to control potentiometrically the exchange of thorium, uranium and lanthanum cations has been studied using electrochenücal and nuclear methods (a counting, RBS). The actual effect of the applied Potential on the exchange process has been demonstrated. The effect of various parameters on the Th cation binding, such as the polymer thickness and the oxidation State of the resin, has also been studied. A low incorporation of uranium has been observed and rationalized by the redox instability of the polymer resin. The reversibility of the Th and La exchange has also been quantified and optimized.