A chemical structured kinetic model for xanthan gum production is proposed involving both the carbon source metabolism and the nitrogen metabolism into the cell. This model considers eight lumped reactions (synthesis of amino acids, both non forming and forming bases, nucleic acids synthesis, both RNA and DNA, xanthan production, total sugar metabolism, oxidative phosphorylation and maintenance energy) and eight key compounds (biomass, ammonium, RNA, DNA, intracellular proteins, xanthan, sucrose and dissolved oxygen). Six runs under different temperatures and different initial nitrogen concentrations have been carried out. Parameter values of the model have been calculated by fitting experimental data of the six runs, using a multiple-response non-linear regression technique coupled to a fourth order Runge-Kutta algorithm. The kinetic model with the parameter values calculated is able to describe in close agreement with experimental data the concentration evolution of the eight key compounds previously mentioned in all the runs performed. Moreover, the structured kinetic model is able to predict the behavior of the system when some operational conditions are changed, such as temperature and initial nitrogen concentration, and also different oxygen transport rates, predicting different xanthan production rates depending on the operational conditions and medium composition (nitrogen source concentration). (C) 2004 Elsevier Inc. All rights reserved.