The production and properties of Agaricus bisporus endoxylanase and β-xylosidase were studied in compost and liquid cultures. A. bisporus was grown on minimal medium with solka floc BW40, oat spelt xylan, Whatman CC41 microcrystalline cellulose, D-xylose and D-glucose as carbon sources. Endoxylanase activity and β-xylosidase activity were found during growth with complex carbon sources such as cellulose or xylan and no activity was present with sugars such as glucose or xylose. In compost culture endoxylanase activity increased during and after the button stage of fruit body development and decreased after fruit body harvest. The production of β-xylosidase differed in that it was only detectable during the button stage of development. Using activity staining and preparative IEF, three endoxylanase activities were separated from liquid cultures and three principal endoxylanase activities were separated from compost extract. The pH optima and IEF profiles of these activities were similar. Only one β-xylosidase activity was found in liquid culture, whereas two were found in compost culture; the IEF profiles of the compost activities differed markedly from those of the β-xylosidase found in liquid culture.