A readily fermentable hydrolysate was prepared by treating corn cobs in sequential steps of autohydrolysis (in aqueous media) and posthydrolysis (in the presence of sulphuric acid). The fermentation of the liquors obtained with this processing scheme by Debaryomyces hansenii resulted in 18% increase in productivity and 25% increase in yield in comparison with the results obtained in fermentation media made by direct prehydrolysis of corn cobs. Two D. hansenii strains were compared for their ability to produce xylitol in media made with autohydrolysis-posthydrolysis liquors. The best strain was adapted to raw and to detoxified, concentrated hydrolysates. Using membrane sterilisation to avoid the thermal degradation of the culture media, productivities up to 1.49 g l(-1) h(-1) and product yields up to 0.73 g g(-1) were obtained in batch cultures carried out at the optimal concentrations of xylose and biomass.