The charge transfer rate for anthraquinonedisulfonate reduction at electrodes modified with poly[1 -methyl-3-(pyrrol-1-yl-methyl)pyridinium] chloride films was determined as a function of the electrode potential, solution pH, and solvent composition by electrochemical impedance spectroscopy. The polycationic film reduced the apparent heterogeneous rate constant of the redox reaction by about two orders of magnitude relative to a naked electrode. This decrease resulted from strong binding of the reacting species to the polymer and a repulsive interaction between the reacting species in the film. On the other hand, the polycationic film extracted a large amount of anthraquinonedisulfonate from an aqueous solution: the partition coefficient amounted to as much as 7 x 10(4). Because of the resulting large increase in the voltammetric current of the redox reaction, the polymer-modified electrodes enabled us to determine traces of the redox species.