High-temperature ignition reactions have been studied behind incident shock waves in equimolar N 2O/H 2 mixtures highly diluted with argon. The infrared emission of N 2O molecules at 4.5 microns behind a shock front was utilized to follow the current concentrations of nitrous oxide, and the transient OH-concentration profiles were determined by monitoring the ultraviolet emission intensity. The experimental data indicate a complicated reaction mechanism in two distinct stages, respectively, at relatively low and high temperatures. In the temperature range of 1400°–2300°K, an induction period is observed in N 2O and N 2O/H 2 systems, the induction times being significantly shorter for the latter case under similar thermal conditions. The importance of chain-branching reaction steps, involving atomic oxygen and hydrogen, is emphasized, and the induction times are evaluated quantitatively. At temperatures above 2000°K, the N 2O-concentration profile features can be satisfactorily interpreted, based on a mechanism which contains the currently accepted data on elementary steps of the N 2O/H 2 reaction, whereas OH emission differs significantly from the assumed mechanism.