Methyl sulfone (MeSO2-) and hydroxylated (OH-) metabolites of polychlorinated biphenyls (PCBs) have emerged as important classes of environmental contaminants in wildlife and humans. The detection of persistent MeSO2-PCBs was first shown in tissues of Baltic grey seal in the mid-1970s. In the last decade the detection and quantification of these metabolites in biota has gained momentum. MeSO2-PCBs are one of the major classes of organochlorine contaminants in humans and several marine and a few terrestrial mammal species. A number of studies have demonstrated the toxicological potential of MeSO2-PCBs including tissue selective retention via non-covalent protein binding, induction of cytochrome P450 enzymes, and endocrine-related effects. More recently OH-PCBs have gained greater scientific notoriety in environmental toxicology as a consequence of the capability of certain OH-PCB congeners to bind with the thyroxine transport protein, transthyretin, and their interaction with thyroid and estrogen hormone receptors. Research on environmentally persistent MeSO2-PCBs and OH-PCB metabolites reported in the last two decades is presented, discussed and summarized. Topics include the relative importance and mechanisms of biochemical formation in the context of PCB biotransformation, physico-chemical properties, and chemical synthesis, nomenclature and analysis. The chemical analysis summary encompasses tissue extraction, compound separation and methods of detection. MeSO2-PCB and OH-PCB toxicokinetics are addressed such as species- and congener-specific formation and clearance, persistence in biota and tissue specific retention. The known biological and toxicological activities of these PCB metabolites are also summarized.