Two species of anaerobic fungi, i.e. Piromyces strain E2 and Neocallimastix patriciarum strain N2, were cultivated in a 10-1 batch fermenter with filter-paper cellulose as the carbon source. The accumulation of fermentation products, production of extracellular protein and (hemi-)cellulolytic enzymes were monitored during growth. Growth of Piromyces E2 in the fermenter resulted in a shift in the fermentation pattern to more acetate and formate and less ethanol, lactate, succinate and malate, possibly because of removal of hydrogen. The specific activities of Avicelase, endoglucanase, beta-glucosidase and xylanase were up to threefold higher compared to small batch cultures. Enzyme activities produced per gram of cellulose were up to four times the values reported for Piromyces E2 grown in a semi-continuous coculture with the methanogen Methanobacterium formicicum. The performance of fermenter enzyme preparations from the anaerobic fungi with respect to hydrolysis of Avicel compared well to that of preparations of Trichoderma reesei. However, addition of exogenous beta-glucosidase was indispensible with the latter preparation for the complete conversion to glucose.