The participation of solid conductive Cu and nonconductive Al2O3 powder particles in charge transfer through a stirred heterogeneous system was studied by means of electrochemical impedance spectroscopy. A different behavior was encountered for Cu and Al2O3 powder particles in a CuSO4 electrolyte. From impedance diagrams, the formation of aggregates and chains of Cu particles is deduced. The important role of the electrochemical reaction taking place at the surface of the particles for the charge transfer behavior in stirred heterogeneous systems must be emphasized. Furthermore, a simple model of a system consisting of nonconducting particles was proposed and, adopting this model, some calculations and comparisons to experimental data were made. (C) 2008 The Electrochemical Society.