The ability of the white rot fungus Phanerochaete chrysosporium to degrade a wide variety of structurally diverse organopollutants is dependent upon the lignin-degrading system of the microorganism. Current research is focused on ways to increase ligninase activity in culture and on understanding the enzymology of the system as it affects xenobiotic oxidation. Ligninase activity is expressed by the fungus in response to nutrient nitrogen limiting conditions. In agitated cultures (1 L total volume in 2.8 L Fernbach flasks), ligninase activities up to 446 units (pmoles of veratryl alcohol oxidized) per liter, representing approximately a 20-fold increase over standard stationary cultures, were observed. Furthermore, ligninase activity was shown to be cyclic, reaching peak activities at about 30-hour intervals. Substantial ligninase activity (200 units/liter) was also observed in 100-mL stationary cultures. In these cultures, veratryl alcohol may serve to induce ligninase biosynthesis, and/or it may protect the enzyme from subsequent inactivation.