Cultures of Streptomyces flavogriseus produced considerable amounts of xylanase when grown on xylan containing media. Comparatively lower yields of this enzyme were obtained when hay or avicel served as main carbon source, β-xylosidase was synthesized intracellularly and appeared less dependent on the fermentation substrate. The strain produced simultaneously various enzymes of the cellulase complex and the xylose induced glucose isomerase.