The ability of two bituminous wastes to modify the plastic properties of a coal has been studied and compared with that of a commercial coal-tar pitch. For the study three coals covering the rank normally used in metallurgical coke production were chosen. The bituminous wastes were obtained from the benzol distillation tower of the by-products section of a coking plant. Thermogravimetry was used to determine the amount of volatile matter that evolves at different temperature ranges. The differences observed in the behaviour of the wastes were explained by examining the composition of the toluene soluble fraction with the aid of gas and liquid chromatography and infrared spectroscopy. It was found that irrespective of softening point, ash content and solubility in organic solvents, the composition of the additives has a decisive influence on the modification of coal plastic stage by bituminous wastes. (C) 2010 Elsevier Ltd. All rights reserved.