The effect of pressure (0.1-1.5 MPa) and oxygen concentration on the growth and viability of Saccharomyces cerevisiae was studied. Cell viability was assessed through the Methylene Blue staining method and the percentages of viable and non-viable cells were estimated using digital image processing. A model taking into account cell viability was developed and used to describe the measured data. The model reveals the opposing effects between oxygen availability and the baric and oxidative stresses present on the system and can successfully describe not only the traditional biomass-product-substrate (X-P-S) evolution but also the ratio of viable cells with time. It is shown that cell viability in general is not constant during the experiments but strongly depends on the environment. (c) 2005 Society of Chemical Industry.