Redox reactions of tris(2,2＇-bipyridine)ruthenium (II) (Ru(bpy)(3)(2+)) as well as charge transport in a Nafion(R) membrane were investigated using potential-step chronocoulospectrometry (PSCCS). The concentration of oxidized Ru(III) obtained from coulometric data was higher than that obtained from spectrophotometric changes, showing that the amount of charge passed does not correspond quantitatively to a real change of the redox center in the electrochemical reaction. Both the charge transport rates obtained from the spectrophotometric and coulometric data were analyzed by a combined process of a physical displacement and charge hopping. It was shown that charge hopping between the complexes takes place predominantly to transport charges in the membrane; the second order rate constant (6.0 x 10(-1) M-1 s(-1)) of the charge hopping obtained from the coulometric data was twice that (2.5 x 10(-1) M-1 s(-1)) calculated from the spectrophotometric data.