This paper reports on the pyrolytic behaviour of raw and microbiologically treated Mengen lignite. Two coal samples were pyrolysed in a thermobalance apparatus at atmospheric pressure. Experiments were carried out dynamically by increasing the temperature from 298 to 1173 K at a heating rate of 20 K min(-1). The data show good behaviour of the microbiologically treated lignite compared with raw lignite. An increase in the activation energy was obtained after microbial removal of sulfur.