The temperatures in the range 1 300°–1 600° K of fuel-rich hydrogen-oxygen flames diluted with nitrogen, supported on a sintered metal matrix, were measured by studying the intensity of emission at 8 521 Å due to added traces of caesium. These temperatures were estimated independently from the heat of reaction and from the measured heat losses to the burner. Discrepancies of up to 100° C observed between the results of the two methods are attributed mainly to errors in the measurement of the heat loss. Adiabatic burning velocities were obtained for the same flames by extrapolation to zero heat loss. The results are in reasonable agreement with other determinations using different methods.