The paper presents synergy effects found during the co-firing of wooden biomass with Bosnian coal types in an experimental reactor. The co-firing tests used spruce sawdust in combination with Kakanj brown coal and a lignite blend of Dubrave lignite and Sikulje lignite. Coal/biomass mixtures at 93:7 and 80:20 wt% were fired in a 20 kW pulverized fuel (PF) entrained flow reactor. Over 20 test trials were performed to investigate ash deposition behavior and emissions under different conditions, varying the process temperature, excess air ratio, and air distribution. During the tests, the temperature in the experimental facility varied between 880 and 1550 degrees C, while the excess air ratio varied between 0.95 and 1.4. There was sufficient combustion efficiency under all co-firing regimes, with burning out at 96.5-99.5% for brown coal-sawdust co-firing. Synergy effects were detected for all co-firing regimes with regard to SO2 emission, as well for slagging at the process temperature suitable for the slag tap furnace. CO2 emissions were also calculated for the blends tested and significant reductions of CO2 found. due to the very low ranking of Bosnian coals. (c) 2008 Elsevier Ltd. All rights reserved.