A large selection of polychlorinated biphenyl (PCB) congeners was determined in tissues from several British bird species including three sea birds, four birds of prey, and herons (Ardea cinerea). The congener “signatures” were consistent between different tissues of the same individual, but varied within and between species. Congeners 138, 153, and 180 were dominant in most samples. Nevertheless, ∑PCB values were wide ranging (0.02–105 μg/g wet weight) and also differed considerably in subsamples of different tissues from individual birds. Applying recently reported toxicity equivalency factors (TEFs) for non-ortho, mono-ortho, and di-ortho substituted PCBs to liver concentrations of such congeners, it appears that the mono-ortho congeners 105 and 118 make a high contribution to TEFs when their toxicities are weighted by concentration. The study highlights that caution is needed when interpreting data on contaminants in wildlife, but suggests that careful sampling will reduce the many variables which can give rise to differing congener patterns and ∑PCB values.