In this study the technique of the Differential Impedance Analysis (DIA) is applied for distinction of two models which give similar impedance diagrams presented with slightly depressed semi-circles-two time-constants Voigt model with high degree of mixing and one time-constant model in which the capacitance is replaced with constant phase element (CPE). Those two models are often used for impedance investigations of solid state. The applicability of the recognition procedure is confirmed on synthetic models as well as on real samples of yttria-stabilized zirconia (YSZ) and Er-doped BaTiO3. (c) 2005 Published by Elsevier B.V..