The agaric basidiomycetes Nematoloma (Hypholoma) frowardii strain b19 and Clitocybula duseni strain b11 were used to produce manganese peroxidase (MnP) in 5, 30- and 300-liter stirred-tank bioreactors. Large amounts of MnP (LIP to 2000 U l(-1)) were gained by using sodium acetate as the major carbon source and by supplementing Mn2+ to stimulate the enzyme production. ln media containing both acetate and glucose, fungi preferred always acetate to glucose as actual carbon source. Both fungi secreted oxalie acid (up to 8 mM) into the medium during the fermentation process. There was no loss in productivity and no significant changes in the isoenzyme pattern during scale up from 5 to 300-liter fermentors. A cyclic batch process has been developed keeping the fungal Cultures in the productive state for Prolonged time and allowing to harvest the enzyme containing culture filtrate every two to three days.