This study deals with ultrafine wet grinding of calcite particles in a stirred head mill. As the size decreases during the process, the particles are strongly subjected to attractive interparticle forces leading to an aggregation phenomenon that generates an increase of the suspension viscosity. In order to improve the process efficiency, the use of grinding aid, such as two polyelectrolytes (sodium polyacrylate (SPA) and polystyrene sulfonate) has been tested. The adsorption of the polymer chains on the particle surface is found to prevent the aggregation through an electrosteric effect, so allowing the suspension viscosity to be reduced. (C) 2004 Elsevier B.V. All rights reserved.