Sawdust, paper and charcoal were pyrolysed in a thermogravimetric analyser in a nitrogen atmosphere at heating rates ranging from 5 to 80 degrees C min(-1). The thermograms for the biomass samples showed different weight-loss characteristics, and in some cases more than one area of weight loss. There was a lateral shift to higher temperatures of thermal degradation with increasing heating rate. Activation energies calculated for all the samples showed a falling trend as the heating rate increased.