The analytical method used for determination of polychlorinated dibenzo-p-dioxins and -furans (PCDDs/Fs) emissions from municipal waste combustors (MWCs) and other stationary sources was modified and validated to additionally allow for analysis of ultratrace levels of polybrominated diphenyl ethers (PBDEs) and polybrominated dibenzo-p-dioxins and -furans (PBDDs/Fs) from a common flue gas sample. Potential methodological problems related to physicochemical properties of brominated compounds, including UV- and temperature-induced debromination and degradation, were addressed. The selection of solvents, optimization of extraction time, and adaptation of the cleanup and fractionation steps increased mean recoveries of (13)C(12)-labeled PBDE and PBDD/F isotope dilution surrogates about 18% and 25%, respectively. The customary liquid chromatography isolation of PBDEs and PBDDs/Fs was replaced by optimization of high-resolution gas chromatography to separate target PBDFs (2,3,7,8-Br-substituted) from potentially interfering PBDEs before mass spectroscopic identification. The optimized method allowed quantitative determination of 56 mono- through decabromodiphenylether congeners, 15 congeners of 2,3,7- and 2,3,7,8-Br-substituted tri- to octabromodibenzo-p-dioxins and -furans, and all 210 polychlorinated dibenzo-p-dioxins and -furans present in the flue gas at levels of picogram to microgram per normalized cubic meter.