Of eight white-rot fungi examined, seven fungi grew on nitrogen-limited poplar wood meal medium and degraded 14C-lignin in wood meal to 14CO2. Increased oxygen enhanced both the rate and extent of degradation. However, whereas Pleurotus ostreatus, Pycnoporus cinnabarinus 115 and Pycnoporus cinnabarinus A-360 degraded 12-17% of 14C-(U)-lignin of poplar wood to 14CO2 also in an air atmosphere, Sporotrichum pulverulentum, Phlebia radiata 79 and Phanerochaete sordida 37 degraded only 1-5% under these conditions. Addition of cellulose and glucose to the poplar wood medium stimulated degradation of 14C-(RING)-lignin of poplar wood by Phlebia radiata 79 but repressed degradation by Polyporus versicolor and Pleurotus ostreatus. Cellulose added to the wood meal medium had no effect on the degradation of lignin by Phanerochaete sordida 37 and Sporotrichum putverulentum but glucose slightly repressed lignin degradation by these fungi. Those white-rot fungi which were considered as preferentially lignin attacking fungi could degrade 14C-(RING)-lignin of poplar wood efficiently under 100% oxygen. They did not require an extra energy source in addition to wood meal polysaccharides for rapid ring cleavage and they degraded up to 50-60% of the 14C-lignin to 14CO2 in 6-7 weeks at a maximum rate of 3-4% per day.