Pinus taeda wood chips were treated with the white-rot fungus Ceriporiopsis subvermispora in 20-dm(3) bioreactors for periods varying from 15 to 90 days. Decayed samples, non-inoculated controls and extractive-free wood samples were submitted to kraft pulping using 25% of sulfidity and different active alkali concentrations in the cooking liquor. Cooking reactions were carried out isothermally at 170degreesC. Residual lignin contents of pulps prepared from biotreated wood chips were lower than those observed in pulps from the undecayed control. Delignification kinetic studies showed that the initial delignification phase was accelerated and shortened by the fungal pretreatment. At a cooking time fixed before the end of the bulk delignification phase, the fungal pretreatment provided pulps with significantly lower kappa numbers or pulps with a fixed kappa number were obtained by reducing the amount of active alkali added to the liquor. Pulps of kappa So were obtained both from the undecayed control cooked with 20.8% of active alkali and from the 15-day-biotreated sample cooked with only 15% of active alkali. The biopulping benefits were neither proportional to the extent of the biodelignification nor to the biological removal of some specific wood component. DFRC-determination (derivatization followed by reductive cleavage) of the amount of aryl-ether linkages in residual lignins of biotreated samples indicated an extensive depolymerization during the initial stages of biodegradation, which suggested that bio-depolymerized lignin was easily released during the first stages of cooking, resulting in a faster and shorter initial delignification phase.