Samples of biofuels produced sep. from hay meadow, stems of Sida hermaphrodita and Miscanthus giganteus as well as three kinds of straw (corn, wheat and oilseed rape) were combusted in a lab. boiler. Energy contents were 16.5-17.6 MJ/kg, depending on the type of used biomass. The CO, NOx and SO2 concns. in the exhaust gas were detd. The lowest concns. (1125, 110 and 24 ppm, resp.) were found in the exhaust gas generated by the combustion of Sida hermaphrodita. The combustion of hay meadow resulted in a gas contg. 3918, 123 and 66 ppm of CO, NOx and SO2, resp.