Sound (undecayed control) and fungally-pretreated wood samples were submitted to organosolv deligni®cation. The cooking liquor used was methanol/water (78:22 v/v) containing CaCl 2 and MgSO 4 each at a concentration of 25 mmol dm À3 . The cooking process was performed at 180 °C for reaction times varying from 5 to 100 min. Despite some differences in the lignin removal pattern, pseudo-®rst order kinetic models permitted a prediction of deligni®cation rate constants for all experiments. All biodegraded samples provided higher deligni®cation rate constants than the undecayed control (2.0 Â 10 À2 min À1 for the undecayed control and, for example, 14.2 Â 10 À2 min À1 for the sample decayed by Trametes versicolor for 2.5 months). Biodegraded samples also presented signi®cantly increased xylan removal rates. The type of biodegradation affected the behavior of wood samples under organosolv pulping. The highest deligni®cation and xylan removal rate constants were observed in the sample decayed by T versicolor for 2.5 months (17% weight loss). However, high deligni®cation and xylan removal rate constants were also observed in the sample decayed by Punctularia artropurpurascens for only 0.5 months (1.2% weight loss). Data obtained from a single fungal species pretreatment or data from all fungal pretreatments indicated that there is no clear correlation between the deligni®cation constants and the wood weight or component losses. This lack of correlation suggested that the structure of residual polymers in decayed wood affects the deligni®cation process in the organosolv pulping more than the removal extent of each individual component.