The agitation power required by Liquid-solid suspensions of large PVC discs (4.3 mm) and sand granules (1.29 mm) in water was measured for various solids concentration, up to 16% by volume, using 5 different impellers. In all cases the dispersed power increased with increasing solids content, more than expected based on the suspension density. The solid phase actually dissipates energy due to particle-liquid friction and in the collisions of the particles. The amount of energy dispersed according to these mechanisms is generally low, but becomes evident with the large particles as the solid concentration increases above 44%.