Two simple one-electron redox reactions, one involving a highly charged ionic reactant, Fe(CN)(6)(4-)- -e(-) reversible arrow Fe(CN)(6)(3-), and the other involving a neutral molecule, Fe(CH2OH)(2) -e(-) reversible arrow Fe(CH2OH)(2)(+) were investigated in a congruently melting electrolyte, (C4H9)(4)NF . 32H(2)O, at temperatures below its melting point. They were studied by cyclic voltammetry and potential step chronoamperometry using a Pt ultramicroelectrode. After freezing, the shape of cyclic voltammograms changes from the near steady-state wave shape typical of radial diffusion to the peak shape typical of linear diffusion. The slow-scan cyclic voltammetric currents obtained in solid electrolyte are considerably smaller than those obtained in liquid electrolyte. Both effects are probably caused by a substantial decrease in the apparent diffusion coefficient of redox species in the solid state. Additionally the results of potential step experiments performed in the solid electrolyte at short times (less than or equal to 1 s) show some radial diffusion contribution. On the basis of these results it has been concluded that the redox reactant is not uniformly dispersed in the solid electrolyte, but is concentrated near the electrode surface and probably in intergrain space.