Xylose production by Candida guilliermondii FTI 20037 was carried out in a synthetic medium in the presence of 0-100 g methanol l(-1), 0-0.7 g furfural l(-1) or 0-1.3 g acetic acid l(-1). Kinetic results show a mixed inhibition mechanism in all three cases. Maximum specific productivity and saturation constant for product formation were, in the absence of inhibition, 3.6 g(P) g(X)(-1) h(-1) and 232 g(S) l(-1), respectively, while the inhibition constants, K-i and K-i', were 17 and 50 g methanol l(-1), 0.62 and 7.0 g furfural l(-1), 0.69 and 3.5 g acetic acid l(-1), which suggests the following order of inhibition: furfural > acetic acid > methanol.