The polyanionic block copolymer of Eastman Kodak, AQ 55, was examined for its ability to incorporate and retain electroactive counterions in both aqueous and non-aqueous (acetonitrile) solutions. The coatings exhibited substantial cation permselectivity : chloride anions were prevented from reaching the underlying electrode to be oxidized but could be oxidized via electron-transfer to Ru(phen)(3)(3+) (phen = 9,10-phenanthroline) cations generated from Ru(phen)(3)(2+) counterions incorporated in the coating of AQ 55. Ru(pdon)(3)(2+) (pdon = 9,10-phenanthroline-5,6-dione) counterions incorporated in coatings of AQ 55 and reduced in acetonitrile to anionic complexes are lost from the coatings much more rapidly than is the original cationic complex.