Measurements of burning velocity and flammability limits in four ternary mixtures containing ammonia (NH 3+H 2+N 2O, NH 3+H 2+NO, NH 3+N 2O+NO, NH 3+N 2O+NO) have been made at sub-atmospheric pressures. Flame speeds relative to the burnt gas (S B) were measured in a closed vessel by schlieren photography with a drum camera. Composition limits of flammability (spark ignitability) were measured for upward propagation in a vertical tube of standard form. The effect upon flame speed of variation in mixture composition over the whole range of flammability was investigated. In two systems (NH 3+H 2+N 2O; NH 3+N 2O+O 2) the composition limits of flammability in ternary mixtures obeyed the le Chatelier rule and the contours of equal flame speed, if displayed on a triangular diagram, reflected the form of the limits. In the other two systems, the composition limits of flammability departed from the le Chatelier rule and the flame-speed contours showed anomalous behaviour. Thus hydrogen apparently inhibited the ignition of NH 3+NO mixtures, and there were signs that the flame speed/composition surface was saddle-shaped. For the NH 3+N 2O+NO system, the oxidants were more effective as a mixture than alone, a maximum flame speed (S B = 1260 cm sec −1) being reached in a near-equimolar (1 NH 3 : 1 N 2O : 1 NO) mixtures. Burning velocities were not significantly affected by total pressure, in concordance with an overall kinetic expression of the second order. There was decomposition of the excess ammonia in rich mixtures, and of the excess nitrous oxide and nitric oxide in lean mixtures. The adiabatic flame temperatures and the equilibrium compositions of the hot products were calculated for stoichiometric mixtures in order to obtain S U, the flame speed relative to the unburnt gases. Previous investigations of flame speed or the related phenomena of slow combustion and spontaneous ignition are compared with the present findings. The salient features of flame chemistry are deduced partly from a comparison between each ternary mixture and the (simpler) constituent binary mixtures, and partly from independent studies of burner flames.