Sludge biogas potential is often reduced by iron-dosing, the extent of the reduction being related to the nature of the sludge and the dosing process. The aim of this research was to develop a rapid laboratory method to measure the impact of iron-dosing on the biogas potential of activated sludge, taking into account the mechanisms that may be decreasing biogas yield. To validate the method, sequential extraction (SE) was used to fractionate iron and phosphorus in the sludge before and after iron-dosing. The laboratory-dosing regime increased total iron and phosphorus in the sludge but decreased their bioavailability, producing sludge with a similar inorganic composition to full-scale chemical P removal (CPR) Sludge, Laboratory-closed Sludge produced 12-20% less biogas and 9-21% less methane when anaerobically digested, in comparison to the same undosed sludge. This method should help water companies and academics to more closely simulate iron-dosing in the laboratory, (C) 2008 Elsevier Ltd. All rights reserved.