The continuous bioconversion of xylose-containing solutions (obtained by acid hydrolysis of barley bran) into xylitol was carried out using the yeast Debaryomyces hansenii under microaerophilic conditions with or without cell recycle. In fermentations without cell recycle, the volumetric productivities ranged from 0.11-0.6 g l(-1) h(-1) were obtained for dilution rates of 0.008-0.088 h(-1). In experiments performed with cell recycle after membrane separation, the optimum xylitol productivity (2.53 g l(-1) h(-1)) was reached at a dilution rate of 0.284 h(-1).