The influence of inorganic constituents on the pyrolysis behavior of different biomass materials and brown coals was studied in a fixed bed reactor within a temperature range of 250-700 degrees C. The tests were carried out with untreated and demineralized samples. Inorganic elements dominant in the used brown coals are calcium, silicon, iron, magnesium, and for some samples also sodium and aluminum. Biomass inorganic constituents mainly involve potassium, silicon and calcium. Nearly total demineralization was accomplished for brown coals via HCl and HF treatment. To prevent exceeding structural changes for biomass materials only HCl was used to remove elements like potassium, magnesium, calcium, and phosphorus. Yields, product composition and HHV were determined for each pyrolysis temperature to create mass and energy balances. Demineralization causes an increase in total liquid yields, while gas yield and char yield (only slightly) decrease. Biomass materials show a stronger effect and main decomposition stage is shifted to higher temperatures. Gas composition is also affected by acid treatment, whereas differences occur between the various fuels. Furthermore, the pyrolysis process becomes more endothermic for the demineralized samples. (C) 2013 Elsevier Ltd. All rights reserved.