A study aimed to monitor the anaerobic digestion process using thermal analysis to define the stability of the digestate obtained was conducted. The mesophilic digestion of primary sludge (PS), of the organic fraction of municipal solid wastes (OFMSW), and of a mixture of these two biowastes was evaluated. Temperature-programmed combustion tests were carried out to investigate the stabilization degree of samples throughout the digestion process. The DTG profile obtained from combustion in an oxidizing atmosphere for the samples analysed showed, as a common result, reduction at low temperatures together with an increase at high temperatures (around 500degreesC) of the intensity of the rate of loss of mass as the stabilization process evolved. In all digestate samples the DTA signal showed energy release at high temperatures (around 500 degreesC) which was not present in feed samples. This study shows that thermogravimetry may offer a means of ascertaining the stabilization degree reached by the organic matter under the anaerobic digestion process. (C) 2004 Elsevier B.V. All rights reserved.