Emissions of CO, NOx and N2O were measured during co-combustion of a mechanically de-watered sewage sludge in a coal-fired circulating-fluidised-bed combustor (CFBC). The test facility had a height of 15 m and was operated at a gas velocity of about 6.3 m s(-1) so that gas residence times similar to those in large-scale combustors were achieved. The combustion chamber, the primary cyclone and the downcomer were heated electrically to compensate for heat losses and thus to ensure uniform temperature throughout the system. The influence on the emissions of CO, NOx and N2O of an addition of wet sewage sludge to a coal-fired CFBC was investigated, and the influences of the operating conditions and the addition of limestone on the emissions were discussed. The measured CO and NOx emissions are compared not only with German emission limits but also with sludge mono-combustion techniques. The result of the investigation is that during co-combustion of wet sewage sludge the emissions of CO and N2O rise, whereas the NOx emission level falls significantly even when only small amounts of wet sewage sludge are added. Increasing the oxygen concentration in the flue gas was a good means of reducing the emission of CO, whereas the N2O emission could be significantly reduced by lowering the superficial gas velocity. With a lowered gas velocity the German emission limits concerning CO can be met over a wide range of sludge-to-coal mass ratios. With respect to NOx, the measured emissions were only half the emission limit over the whole range of sludge-to-coal mass ratios.