The main agricultural residues of Crete are considered to be of premium importance for local energy production through combustion. The thermal behaviour of ashes was predicted by chemical, mineralogical, microscopical and thermal analyses, while the removal of troublesome elements to reduce slagging and fouling in furnaces was tested by leaching these biomass fuels with water. Deposition tendencies were predicted through the use of empirical indices for biomass type ashes. The characterization of the samples showed that these are low in ash and sulfur contents, their ash being rich in CaO, K2O, P2O5 and Ni. Leaching with water resulted in significant reductions in ash (up to 40%), problematic elements K (up to 93%), Na (up to 96%), P (up to 85%) and Cl (up to 97%) and heavy metals Co, U, Mo, Pb and As, as well as improved fusibility behaviour. A lower combustion temperature or water leaching substantially reduced the fouling potential due to alkali, indicating that no ash-related problems should be expected in combustion boilers firing the treated agroresidues studied. (C) 2004 Elsevier Ltd. All rights reserved.