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 gP gX −1 h−1 and 232 gS 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.