The aim of this work was to investigate the influence of the culture growth stage on the inactivation kinetics of Escherichia coli and Saccharomyces cerevisiae using supercritical carbon dioxide (SC-CO2)and to find models that can describe and predict the inactivation behavior of these microorganisms considering the growth stage as one of the model parameters. Cultures of E. coil and S. cerevisiae were grown to four different growth stages: early exponential phase, intermediate exponential phase, late exponential phase and early stationary phase and then treated with SC-CO2 at 350 bar and 35 degrees C. The inactivation kinetics of S. cerevisiae and E. coli showed that the SC-CO2 resistance increased progressively as the growth phase advanced. For both microorganisms, the length of the lag phase increased progressively as the growth phase advanced, not appearing at all in the earliest growth stages. For S. cerevisiae, an equation based on the Gompertz Function satisfactorily described (R-avg.(2) = 0.96; RMSEavg. = 0.48) the inactivation kinetics of this microorganism for the four growth stages selected. Similarly, a single equation that included the dependence on the growth stage was obtained for E. coil, based on the Weibull Function (R-avg.(2) = 0.96; RMSEavg.. = 0.53). The results reveal that the inactivation kinetics using SC-CO2 are greatly influenced by the growth stage and the application of the developed models could be used to find the optimal process conditions according to the cell's growth stage. (C) 2012 Elsevier B.V. All rights reserved.