The application of detailed reaction mechanisms for modelling laminar Barnes takes an extensive computational effort. Ln turbulent flames the interaction between turbulence and fast chemistry leads to additional modelling problems. Reduced reaction mechanisms are therefore needed for modelling laminar and turbulent flames. Two methods to reduce a H-2 and CO/H-2 reaction mechanism are compared. The recently developed ILDM method (Maas and Pope, 1992) is compared with the more conventional method of applying steady-state assumptions for intermediate species (Peters and Rogg, 1993). The results of both reduction methods agree well with detailed computations of adiabatic one-dimensional flames. In the composition space the differences between the adiabatic one-dimensional flame and perfectly-stirred reactor results are small. This indicates that reduced mechanisms will be appropriate for modelling turbulent flames as well.