The filtration of a kaolin suspension and the electroosmosic dehydration of a formed cake are studied. The influence of chemical pretreatments upon these two stages is studied for various added compounds: salts, acids, coagulants, flocculants, and surfactants. The main parameters of the process, such as the cake specific resistance, the energy consumption, and the cake dryness, are compared. The added compounds influence the process parameters differently. The choice of an appropriate method of pretreatment depends on which of these process parameters is of interest to improve. However, with an appropriate pretreatment, electroosmotic dehydration allows cake dryness to be markedly increased at low energy consumption.