Microbial communities grow more stably when they are associated to surfaces or organized in aggregates. This advantage of biofilms is technically exploited for the degradation of xenobiotics or in biocatalysis, where the fixed biomass has the added advantage of easier separation of excreted products. Whereas the biothermodynamic analysis of growth and product formation of suspended cells is developing fast, there are only few reports on the calorimetric analysis and biothermodynamic interpretation of biofilm evolution. Experiments illustrate the ability of calorimetry to monitor the physiological state of biofilms in real time. Sessile cells of Escherichia coli DH5 alpha DSM 6897 were selected as surrogates of biofilm formers of medical, ecological and biotechnological importance. It is explained how stoichiometric information can be extracted from calorimetric measurements and future possibilities are discussed. (C) 2007 Elsevier B.V. All rights reserved.