The unique properties of water at elevated temperatures and pressures, namely the alterability of ionic product, dielectric constant, and density, make it an interesting and promising reaction medium. Several investigations have been made in order to obtain valuable products from biopolymers or, more general, biomass. Biopolymers can react with high-temperature water in very short residence times and with high rates of conversion. The achievable products are manifold and can be varied to a large extent by changing the operating conditions. The possibilities of sub- and supercritical water can even be significantly expanded by adding carbon dioxide since it reacts to carbonic acid, which serves as a catalyst. This work deals with the hydrolysis kinetics of different kinds of biopolymers, namely starch, cellulose (polysaccharides), and proteins (polypeptides). Kinetics was conducted over a broad range of experimental conditions using a continuous-flow reactor. In all three cases, the obtained experimental results could be described by a reaction model according to the approach of a single consecutive reaction following first order kinetics. The rate constants of the hydrolytic conversion were determined for the resulting monomers (glucose and amino acids), and the values were found to strongly depend on the type of bond. The peptide bonds in proteins exhibited a much higher stability compared to the beta-1,4- and beta-1,6-glycosidic linkages in cellulose and starch, respectively. The stability of the resulting monomers and their conversion to further degradation products were determined. The addition of carbon dioxide to water under hydrothermal conditions resulted in a significant increase in acid catalyzed reaction rates, which could be confirmed by the obtained rate constants. (C) 2007 Elsevier B.V. All rights reserved.