The theory of thermoelectrochemical impedance (TEI) was developed and results of calculations were compared with experimental data for the [Fe(CN)(6)](3-/4-) redox system. The validity of the relation Z(i)/Z(phi) = -Z(e) (where Z(i) and Z(phi) are the TEIs in the galvanostatic and potentiostatic regimes, respectively, and Z(e) is the electrochemical impedance of the system) was proved. From the frequency dependence of Z(i) at equilibrium the Peltier heats evolved at different branches of the equivalent circuit were found. From the frequency response spectra obtained under the limiting current conditions the relaxation time and the thickness of the boundary layer, as well as the activation energy of diffusion, were estimated.