Aim of this work was the optimization of xylitol production by Debaryomyces hansenii UFV-170, which already proved to be a new promising xylitol-producing yeast. Two sets of batch bioconversion tests were carried out on synthetic medium, according to two joined 3 3 and 3 2 type full factorial designs, selecting the initial xylose concentration (SO), rotational speed (v) and starting biomass concentration (X-0) as independent variables and the maximum xylitol concentration (P), xylitol yield on consumed xylose (Y-P/S), volumetric productivity (Q(P)) and specific productivity (q(P)) as response variables. The collected results were then worked out by response surface methodology (RSM). Overall optimization, conducted by overlaying the curves of the responses under investigation, allowed us to point out an optimal range of the independent variables within which the four responses were simultaneously optimized. The point chosen as representative of this optimal area corresponded to S-0 = 156 g L-1, nu = 280 rpm and X-0 = 6.4 g L-1, conditions under which the model predicted P = 116.25 g L-1, Y-P/S = 0.77 g g(-1), Q(P) = 1.49 g L-1 h(-1) and q(P) = 0.16 g g(-1) h(-1). (c) 2005 Elsevier Ltd. All rights reserved.