The Discrete Element Method (DEM) has the potential to be a powerful tool for the design and optimisation of mills. However, for DEM to gain acceptance within the minerals processing industry, it is necessary to show that the results obtained from a DEM simulation are valid, and that this validity extends over a wide range of mill operating conditions. Real grinding mills are complex multi-phase devices with a range of particle dynamics and material processes that depend on the exact operating point of the mill. Mill conditions will generally vary statistically over time. It is therefore difficult in this type of environment to systematically verify DEM, where some degree of precision in the mill operation is required. With these considerations in mind a programme of both experimental and DEM simulation work was developed. A " two-dimensional" laboratory mill was built in such a way that precise power measurement and monitoring of charge motion was possible. DEM simulation runs were matched to the experimental conditions. In this account of the work, particular attention is given to the effect of mill speed on power and charge motion, and also of particle behaviour at mill speeds above the critical. DEM predicts the power draft and charge motion of the mill well at speeds below the critical speed. At super-critical speeds, the centrifuging of material in the load was predicted, but power predictions were not as accurate. (C) 2001 Elsevier Science B.V. All rights reserved.