Xylitol production by Pichia stipitis FPL-YS30, a xyl3-Delta 1 mutant that metabolizes xylose using an alternative metabolic pathway, was investigated under aerobic and oxygen-limited culture conditions. Under both culture conditions, FPL-YS30 (xyl3-Delta 1) produced a negligible amount of ethanol and converted xylose mainly into xylitol with comparable yields (0.30 and 0.27 g xylitol/g xylose). However, xylose consumption increased five-fold under aerobic compared to oxygen-limited conditions. This suggests that the efficiency of the alternative route of xylose assimilation is affected by respiration. As a result, the FPL-YS30 strain produced 26 g/l of xylitol, and exhibited a higher volumetric productivity (0.22 g xylitol l(-1) h(-1)) under aerobic conditions.