The concentration influence of some commercial polyethylenimines, used as retention agents, on the retention efficiency during the sheet formation is studied in this paper. The conditions of an industrial wire end have been simulated by means of a dynamic jar of exclusive design. Measurements of the zeta potential have been taken to quantify the surface charge of particles and the colloid titration ratio (quotient between the cationic demand and the anionic demand of pulp slurries) has been evaluated. Both techniques have proved convenient to monitor the retention level; therefore, they are efficient methods to control the retention level in the sheet formation. The univocal relation existing between zeta potential and the logarithm of the colloid titration ratio has been demonstrated. Finally, the variation of the level of turbulence has proved the importance of the hydrodynamics factors in the retention.