Representing typical flame retardants, bromkal 70 DE and 70-5-DE (brominated diphenylethers), Bromkal G1 (pentabromodiphenylether), FR 300 BA (decabromodiphenylether) and Fire Master BP-6 (hexabromobiphenyl) were heated in a quartz tube at 700°C, 800°C and 900°C, and their residues were tested for PBDD and PBDF. Mono- to penta-BDF as well as mono- to tetra-BDD were found in yields of up to 90% in Bromkal 70 DE, 70-5-DE and Bromkal G1. The optimal temperatures of formation hereby were between 700°C and 800°C. The residues of decabromodiphenyloxide contained tetra- to octa-BDF along with hepta- and octa-BDD, whereby the optimal formation temperatures were 800°C and 900°C. Furthermore, the pyrolysis of hexabromobiphenyl yielded di- to hepta-BDF. In a second series of tests, flame retardants were mixed with polystyrene and polyethylene, melted at 200°C and then pyrolyzed at 700°C, 800°C and 900°C. The residues of the mixtures polystyrene/Bromkal 70-5-DE and polyethylene/Bromkal 70-5-DE contained mono- to penta-BDF congeners. Mono-, di-, tri- and tetra-BDF could be detected in the pyrolysates of polystyrene- and polyethylene-decabromodiphenylether. The analysis of the polystyrene- and polyethylene-hexabromobiphenyl pyrolysates yielded mono- to tetra-BDF.