Several hydrogen/air reaction systems are reduced mathematically to one-step schemes, using the method introduced by Maas and Pope . The reduction is obtained by assuming fast reaction groups of the reaction system to be in steady state. We developed a method to apply the reduced schemes to adiabatic flat flames. The results are compared with those of detailed chemistry calculations. The accuracy of the results of reduction of the most simple reaction system, (which does not include the species HO2 and H2O2) is quite well. The other reaction systems, however, give appreciable errors in burning velocity. This is mainly caused by large deviations in HO2 mole fractions between reduced and full scheme calculations, while the reaction rate and the burning velocity are sensitive to variations in the mole fraction of HO2. Considering the time scales of the reaction system and the time scales of convection and diffusion it is shown that at low temperatures, where the mole fraction of HO2 reaches its maximum, the basic assumptions applied to reduce the mechanisms are not justified. It is concluded that the hydrogen/air system can only be reduced to an accurate one-step reduced scheme, if reaction schemes without HO2 and H2O2 are used. This reduction technique also indicates, in accordance with conclusions of Peters et al. , that a two-step reduced scheme has to be used if more realistic hydrogen/air schemes, including HO2 and H2O2, are considered.