Pichia guilliermondii strain NRRL Y-12723 fermented mixtures of xylose and arabinose to form xylitol and arabitol. However, cultures grown on a mixture of glucose, xylose and arabinose, in ratios characteristic of corn fibre hydrolysates, preferentially utilised glucose and only slowly metabolised pentose sugars, with low yields of sugar alcohols. A two-stage, sequential fermentation scheme for the production of xylitol and arabitol from a mixture of sugars was developed. Following glucose consumption, cells were removed from mixed sugar cultures and replaced with cells from cultures grown on xylose alone. In the second fermentation stage, xylose and arabinose were successfully fermented to xylitol and arabitol. Dilute acid hydrolysates of corn fibre were suitable substrates for the two-stage fermentation process, but only after treatment with a mixed-bed deionization resin. (C) 2000 Elsevier Science Ltd. All rights reserved.