In this work, the methodology for quantification of water-soluble species in ash was evaluated by varying the parameters leaching time, liquid-to-solid ratio, and size reduction by grinding. The basis for the methodology is a modification of Tessier's sequential extraction method. This work concentrated on fly ashes from combustion of MSW in a fluidised bed boiler, and generally the amounts of water-soluble forms of metals in the ashes were low. Longer leaching time generally reduced the amount of water-soluble metal detected, showing the importance of adsorption and re-precipitation processes. The effects of the L/S parameter and of grinding seem to be dependent on the characteristics of the ash matrix. (c) 2006 Elsevier Ltd. All rights reserved.