The effect of non-isobaric short-time pre-hydrolysis of Siberian type wood and wood bark (Populus tremula wood, Larix sibirica bark, Abies sibirica bark) on the isolation of different organic substances was studied. From Populus tremula wood, activated at 187-240 degrees C and 1.2-3.4 MPa, cellulose and sugar solution were isolated with yields up to 50 wt%, and II wt%, respectively. The composition of water-soluble compounds was studied by chemical and chromatographic methods. The main compounds were represented by mono- and oligo-saccharides, low molecular mass lignin, acetic acid, furfural and other products of sugar destruction. Methanol, isopropanol, propionic acid and hydroxymethylfurfural were formed in small amounts. The non-isobaric pre-hydrolysis of coniferous bark promoted the ct-traction process and increased the yield of extracted compounds. Some information on functional composition of extracts was obtained by NMR and IR spectroscopy. An integrated technology for wasteless processing of coniferous wood bark was suggested based on the combination of non-isobaric steam activation of bark, extractive isolation of some groups of organic substances, and oxidative pyrolysis of solid residue in a fluidized bed of catalyst. Copyright (C) 1997 Elsevier Science Ltd.