The sound pyrometry uses as acoustic temperature measuring technique the dependence of the speed of sound on the temperature of a sound-treated gas in order to determine temperatures and temperature distributions in combustion chambers. During an investigation period of several months, the temperature differences in the combustion chamber of a lignite-fired power station boiler with an electric capacity of 600 MW were determined at different operational conditions with the aid of sound pyrometry. The effect of the relation between mills and burner. the flue gas recirculation, the burn-up air and the coal quality on the temperature distribution was determined. The determined temperature distributions were correlated with the boiler pollution and the NO(x) emission.