Electrophoretic deposition (EPD) of colloidal ZrO2 ceramic powder was examined with respect to the internal colloidal forces and the external electrical field. The influence of electrolytic dissociation of water close to the deposition electrode (cathode) on the electrostatic interaction between the particles and the local electric field is discussed. The discrete element method (DEM) was used to get an insight into the kinetics determining particle packing and density gradient microstructures. The simulation indicates that high particle concentrations combined with low electric field strength result in coagulated flocs and a low packing density in the deposit layer. Tentative phase diagrams for various colloidal forces and electrical field strengths were established. (C) 2004 Kluwer Academic Publishers.