Saccharomyces cerevisiae is an important model to understand the eukaryotic cells control mechanisms. In this Letter, an approach based on in vivo C-13 NMR and mathematical modelling was presented to develop a basis for a deeper understanding of eukaryotic responses to environmental stresses. Despite the few metabolites included, the model describes correctly the dynamical behaviour of glucose degradation and ethanol production, providing a qualitative and quantitative description of the response of S. cerevisiae metabolism to stressful concentrations of ethanol. The data and the model highlight that an exogenous stress is able to influence the cellular activity and the ethanol production rate constant. (C) 2004 Elsevier B.V. All rights reserved.