Clostridium sp. SAIV produces a high level of extracellular xylanase when grown on either xylan or xylose (520 and 480 mU ml-1). β-Xylosidase enzyme is cell-bound. Clostridium sp.SAIV showed growth on filter paper cellulose, but growth decreased with repeated transfer on this substrate. However, cellulase enzymes were expressed and continued degradation of cellulose occurred when the organism was grown on xylose plus cellulose. © 1991.