The effects of different parameters on extracellular xylanase biosynthesis by Trichosporon cutaneum SL409 were studied. Addition of wheat bran and Tween 80 to the medium stimulated enzyme biosynthesis significantly. The highest xylanase activity obtained in liquid culture was 74 IU/ml. The xylanase appeared to be homogeneous after ethanol precipitation and chromatography on DEAE-cellulose and Sephadex G-75 but it exhibited some microheterogeneity on polyacrylamide gel electrophoresis. Enzyme activity was optimal at pH 6.5 and 50 degrees C, and completely inhibited by Hg2+. Cu2+, Fe2+, Zn2+ and Mn2+ also showed significant inhibitory effects. No inhibitation was observed with Mg2+, Ca2+ and EDTA at 1 mM.