An on-line (in situ) viscosity follow-up technique was developed in the framework of the makedown of highly concentrated slurries. The effect of powder feeding rate and the solid content on the power consumption and the slurry viscosity was examined. The feeding rate is shown to be a key parameter from an economical standpoint, since a power consumption peak appears at the end of incorporation, whose magnitude is directly related to the feeding rate. The slurry viscosity also increases dramatically at the end of powder incorporation, especially for a high feeding rate. The time change of the on-line shear viscosity follows the variation of the dispersing torque during the whole incorporation process. Finally, the eventual on-line shear viscosity is in good agreement with an off-line viscosity evaluated at equivalent shear rate.