Owing to government demand, ELSAM (the power pool of the western part of Denmark) is obliged to utilize large amounts of biofuels for power production. Straw and wood chips are the most abundant biofuels in Denmark, and an overview of fuel composition in comparison with coal is given. The high content of potassium and chlorine in straw causes a number of serious technical problems in power production plants and therefore the possibility of reducing the content of potassium and chlorine in straw has been investigated. Cultivation trials were established in the growing seasons of 1993 and 1994. In the first part of the project, the way in which different cultivation factors influence the chemical composition of straw was investigated. Selected samples of grain were also analysed. In the second part of the project, the aim was to study how chlorine supply with fertilizers influences the straw composition. The major conclusions of the investigations are: that no correlation is seen between the content of potassium and chlorine in straw and soil type, nitrogen and potassium fertilizer dose, pesticide dose and geographic location; that there is a strong correlation between chlorine content in straw and supply of chlorine with fertilizer; that the content of potassium and chlorine is dependent on the variety; that rain after harvest leaches significant amounts of potassium and chlorine from straw lying in the field; and that grain has a lower content of ash, K, Ca, Si and Cl than straw, but a higher content of N. (C) 1997 Elsevier Science Ltd.