In the thermal drying of wet biomass with steam or flue gases prior to conversion or combustion, organic compounds are released and constitute a load on the environment as emissions to the air or as effluents to natural waters. They can also cause operational problems by contributing to the formation of deposits in downstream sections. The release of these organic detrimental substances was studied both under atmospheric and pressurized conditions. Laboratory-scale fluidized-bed drying experiments were carried out at the temperature range of 150 – 350 °C for pine and birch barks and peat. The hydrophilic and lipophilic compounds released were analyzed by different chromatographic methods. In addition, dust, deposit and condensate samples from industrial bark and peat dryers were analyzed.