The eucalyptus hemicellulose fraction was hydrolyzed by treating eucalyptus wood chips with 1.2% (v/v) sulfuric acid (wood to acid ratio of 1:3) at 150 degrees C for 120 min. The hydrolyzate was used as substrate to grow Paecilomyces variotii IOC-3764 in a 7-1 fermenter at 30 degrees C; air 1.5 vvm; stirring 400 rpm. The kinetic parameters measured included maximum growth rate (mu(max) 0.10/h) yield (Y-x/s, 0.44 g/g), and productivity (Q(x) 0.26 g/l.h). The protein produced (34% of the biomass) contained all essential amino acids for animal feed.