The effects of PSS (sodium polystyrene sulphonate) and NSF (naphtalene sulfonate formaldehyde condensate) chemicals used to control the pulp rheology, on the grindability of coals were studied. Zonguldak region bituminous coal and Istanbul region brown coal samples, which have different structures, were used in the test work. Wet grinding tests with two coal samples were performed with and without PSS and NSF under constant grinding conditions; the solid ratios ranged from 50 to 60% with 0-60 min grinding periods. The grinding conditions in the preparation of coal-water slurries were improved by the use of the dispersing agents PSS and NSF and viscosity values much less than 1000 mPa were obtained. Under the optimum concentrations (0.3 and 0.7% to mass of coal) attainable in the presence of PSS and NSF, it was observed that the conservation of energy would be 70% with coal from Zonguldak and 60% with that from Istanbul if PSS were present in the grinding medium. On the other hand, the values obtained in the presence of NSF were 45 and 47%, respectively. (c) 2005 Elsevier Ltd. All rights reserved.