An NAD(+)-dependent xylitol dehydrogenase (XDH) from Fusarium oxysporum, a key enzyme in the conversion of xylose to ethanol, was purified to homogeneity and characterised. It was homodimeric with a subunit of M-r 48 000, and pI 3.6. It was optimally active at 45degreesC and pH 9-10. It was fully stable at pH 6-7 for 24 h and 30degreesC. K-m values for D-xylitol and NAD(+) were 94 mM and 0.14 mM, respectively. Mn2+ at 10 mM increased XDH activity 2-fold and Cu2+ at 10 mM inhibited activity completely.