The first experimental measurements of the influence of manganese- and tin-containing compounds (MMT, TMT) on the burning velocity of methane/air flames are presented. Comparisons with Fe(CO)(5) and CF3Br demonstrate that manganese and tin-containing compounds are effective inhibitors. The inhibition efficiency of MMT is about a factor of two less than that of iron pentacarbonyl, and that of TMT is about 26 times less effective, although TMT is still about mice as effective as CF3Br. There exist conditions for which both MMT and TMT show a loss of effectiveness beyond that expected because of radical depletion, and the cause is believed to be particle formation. Kinetic models describing the inhibition mechanisms of manganese- and tin-containing compounds are suggested. Simulations of MMT- and TMT-inhihited flames show reasonable agreement with experimental data. The decomposition of the parent molecule for the tin and manganese species is found to have a small effect on the inhibition properties for the concentrations in this work. The inhibition effect of TMT is determined mostly by the rate of the association reaction H + SnO + M <----> SnOH + M, and the catalytic recombination cycle is completed by the reactions SnOH + H <----> SnO + H-2 and SnOH + OH <----> SnO + H2O. The inhibition mechanism by manganese-containing compounds includes the reactions: MnO + H2O <----> Mn(OH)(2); Mn(OH)(2) + H <----> MnOH + H2O, and MnOH + OH (or H) <----> MnO + H2O (or H-2), and the burning velocity is most sensitive to the rate of the reaction Mn(OH)(2) + H <----> MnOH + H2O.