The co-pyrolysis of coal-biomass blends were studied by using thermogravimetric analysis to look for thermal events indicating interactions that could cause synergic or inhibitory effects during the first stage in the co-combustion of these materials. Two coals from different rank were selected for the Study and combined with radiata pine sawdust, the selected biomass compound. Pyrolysis assays were carried out on the individual components and the binary coal-sawdust blends (50% p/p) at different heating rates (10, 30. 50 degrees C/min) until reaching a maximum temperature of 1200 degrees C. The individual components behaved as expected and as is widely described in the specialized literature. Interactions detected in the blends resulted in greater-than-expected volatile yield values. These interactions were produced at pyrolysis temperatures over 400 degrees C, when most of the components in the blend are devolatilized, and are attributed to secondary reactions that inhibit the formation of chat. (C) 2008 Elsevier B.V. All rights reserved.