Production of extracellular inulinase by low-cell-density (2 kg dry weight.m(-3)) sucrose-limited chemostat cultures of Kluyveromyces marxianus obeyed saturated kinetics at dilution rates ranging from 0.02 to 0.5 h(-1). A non-structured Monod-type equation, describing the relation between specific growth rate and specific extracellular-inulinase production rate, was used to fit experimental data. This equation was subsequently incorporated in a model for the production of biomass and extracellular inulinase in a high-cell-density (> 100 kg dry weight.m(-3)) fed-batch culture of K. marxianus grown on sucrose. The model adequately described biomass production in the fed-batch culture. However, the production of extracellular inulinase in the fed-batch process was slightly higher than predicted by the model. This observation may be related to differences in growth conditions between in the chemostat and fed-batch cultures.