The white-rot fungus Trametes multicolor MB 49 has been identified as an excellent producer of the industrially important enzyme laccase. The formation of extracellular laccase could be considerably stimulated by the addition of Cu(II) to a simple, glycerol-based culture medium. In this study, optimal concentrations of copper were found to be 0.5-1 mM, which were added during the growth phase of the fungus. Other medium components important for laccase production are the carbon and nitrogen sources employed. When using an optimized medium containing glycerol (40 g/L), peptone from meat (15 g/L), and MgSO(4)(.)7H(2)O and stimulating enzyme formation by the addition of 1.0 mM Cu, maximal laccase activities obtained in shake-flask cultures were approx 85 U/mL. These results, however, could not be scaled up to a laboratory fermentor cultivation. Laccase production by T. multicolor decreased considerably when the fungus was grown in a stirred-tank reactor, presumably because of damage of the mycelia caused by shear stress and/or changes in the morphology of the fungus.