Maximum activities of manganese-dependent peroxidase (MnP) and lignin peroxidase (LiP) in free cultures of Phanerochaete chrysosporium (ATCC 24725) were 258 U l(-1) and 103 U l(-1), respectively, in an airlift bioreactor. Immobilisation of the fungus on an inert carrier as well as several design modifications of the bioreactor employed gave MnP activities around 500-600 U l(-1) during 9 days' operation. The continuous operation of the latter led to MnP and LiP activities about 140 U l(-1) and 100 U l(-1), respectively, for two months, without operational problems. Furthermore, the extracellular liquid secreted decolourised the polymeric dye Poly R-478 about 56%.