Pyrolysis/gas chromatography/mass spectrometry was used to elucidate the ability of streptomycetes to modify pine wood under solid-state fermentation. The pyrograms of sound and decayed wood showed the typical pyrolysis products derived from carbohydrates and lignin. In general, the relative abundance of the former was lower in treated woods than in sound wood. Several major peaks released from guaiacyl units of lignin were also revealed. Although some differences could be observed in the relative abundance of the released guaiacyl units from lignin between sound and treated woods, a clear decrease in the lignin-derived products by the action of the microorganisms was not observed. Nevertheless, an increase in the relative abundance of the most of guaiacyl units with a higher oxidation degree was mainly detected in woods treated by the strains Streptomyces UAH 7, Streptomyces anulatus, Streptomyces UAH 48, Streptomyces avermitilis and Streptomyces badius. These results suggest an oxidative action of these strains on the lignin of pine wood, which was corroborated by a decrease in the (aldehyde/ ketone + acid) ratio. In addition, the breakdown of the alkyl chain linkages by the strain Streptomyces UAH 7 could be also observed. Analytical pyrolysis allow to demonstrate for first time the oxidative attack of selected Streptomyces strains on lignin moiety of pine wood, which is an important requirement for biomechanical pulping purposes. (C) 2005 Elsevier B.V. All rights reserved.