In laboratory tests, feed materials are normally ground in batch mills in the belief that constant conditions in the tests reveal the true properties of the materials. This paper presents a new laboratory-scale, continuous classifying mill developed at the Technical Research Centre of Finland (VTT), Mineral Processing, together with results obtained from treating different types of ore. The study was started at VTT＇s own initiative and financed by VTT during the period 1991-1994. The results of this study show that the new continuous classifying mill offers much greater scope for control in grinding research work than a batch mill (e.g. pH, redox potential, and grain size distribution of the milled product). New factors influencing grinding phenomena have been studied and used to improve product grain size distribution and mill throughput control. Several nickel, copper, oxidic, and industrial mineral ore types have been tested by changing the ball charge in the mill, the feed rate, and the water/solids ratio in the feed. The results indicate that it might be possible to increase milling capacity without sliming the fines in the product and at the same time to improve the energy efficiency of grinding. The difference was very significant under optimum grinding conditions, especially with very soft feed materials such as those containing serpentine, carbonate or talc.