The production of extracellular inulinase (13-1,2-D-fructan fructanohydrolase, EC 3.2.1.7) was stud-ied in fed-batch cultures of the yeast Kluyveromyces marxianus CBS 6556 at 30 and at 40 ° C. At both tem-peratures, the final biomass concentration exceeded 100 g.1 -I and more than 2 g enzyme. L -1 of culture su-pernatant was produced. The biomass yield on 02 at 40°C was substantially lower than at 30 ° C. Neverthe-less, at 40°C a growth rate of 0.20 h -1 could be main-tained for a longer period than at 30 ° C. The unex-pected higher O2-transfer rate at 40°C is probably due to a lower viscosity of the culture broth. The 40 ° C fer-mentation took only 33 h as compared to 42 h at 30 ° C. These results indicate that K. marxianus is a promising host for the extracellular production of heterologous proteins under the control of the inulinase promoter.