The polybrominated biphenyl (PBB) constituents of Firemaster FF-1 were determined using gas chromatography-electron capture (GC-EC). The absolute and relative retention times of each of eight major constituents were obtained. It was shown that 2,2',5,5'-tetrabromobiphenyl was a suitable internal standard for the quantitative analysis of the PBBs in Firemaster FF-1 in mammalian tissues and fluids.