Biodegradation of softwood (Pinus radiata) by the ascomycete Chrysonilia sitophila was dependent on the nitrogen and glucose concentrations in the culture medium. Optimization studies of the delignification process, in which the nitrogen (0–50mmol/l NH+4) and glucose (0–2%) concentrations were varied, showed a maximal value of 17·8% for sawdust degradation in cultures containing 10 mmol/l NH4+and 1·0% glucose. Solubility of the decayed sawdust in 1% NaOH at maximal delignification conditions showed a threefold increase and changes in the thermogravimetric pattern were also observed. Biodegraded wood chips showed significant decreases of the 280 and 310 nm characteristic lignin bands in the u.v. reflectance spectra.