FireMaster BP-6 is a commercial polybrominated biphenyl (PBB) preparation containing a complex mixture of isomers with the major component being identified as 2,2',4,4',5,5'-hexabromobiphenyl. Column chromatographic techniques have been developed in which the crude FireMaster is separated into three fractions, F1, F2, and F3, in increasing order of polarity. F1 consists of highly purified 2,2',4,4',5,5'-hexabromobiphenyl (94%) whereas F2-F3 contain less of this isomer and correspondingly more of the other bromobiphenyl components. Previously we have shown that crude FireMaster BP-6 is metabolized in mammals to give hydroxylated degradation products and the metabolism of F1, not unexpectedly, gives comparable results. It is well known that PBBs are effective inducers of diverse microsomal enzymes including including the aryl hydrocarbon hydroxylase (AHH) system. The effects of FireMaster BP-6 and F1-F3 as AHH inducers have been investigated by using the following approach: the substrates used to monitor AHH activity are model halogenated aromatic compounds; the levels of metabolites and metabolite conjugates formed have been quantitated for control and induced enzymes; the levels of macromolecular adducts have also been quantitated for the inducers. This approach thus not only measures the rate of increase of detoxification products (metabolites and metabolite conjugates) but also monitors the macromolecule adduct formation which represents a toxification route. The effects of the PBBs as AHH inducers will be discussed in terms of the above approach.