The aim of this study was to show the link between the initial characteristics of waste activated sludge (WAS) samples and their thermophilic anaerobic biodegradabilities, as determined by biochemical methane potential (BMP) tests, in order to develop relevant prediction indicators. Macroscopic parameters, biochemical composition and a fractionation of total solids by the Van Soest method were carried out on WAS samples which were taken from the inlet and outlet of full-scale sludge anaerobic digesters. Biodegradability was expressed as a function of WAS characteristics by the partial least square (PLS) regression technique. Among several PLS models, the most appropriated model was based on biochemical characterisation (carbohydrates, lipids and proteins) and two macroscopic parameters (soluble organic carbon and the ratio of chemical oxygen demand to total organic carbon). The biodegradability indicators developed in this study permitted the prediction of the methane production from WAS samples. (C) 2010 Elsevier B.V. All rights reserved.