The rheological properties of stirred mill slurries with different solid content, particle size and size distribution are determined and modeled. The flow properties ranged from shear thinning to yield shear thinning with increasing solid content and decreasing particle size. In contrast to other reports on the rheology of grinding mill pulps, dilatant properties were not observed. The flow properties are best characterized by the Casson model as compared to the Bingham. The research confirms "first-order" breakage rates in stirred mills. The yield stress is the dominant rheological parameter and strongly affects the power draw, particle breakage rate, net production of fines (-10 mum) and the product size distribution. An increase in the yield stress corresponded to an increase in power draw a decrease in breakage rate decrease production of fines and a narrower particle size distribution. The ability to affect particle size distribution by controlling the pulp rheology and potential consequences to downstream flotation and dewatering processes. (C) 2004 Elsevier Ltd. All rights reserved.