To provide data on the degree of contamination of the marine ecosystem isomer-specific concentrations of polychlorinated biphenyls, including planar, mono- and di-ortho congeners, were measured in the Weddell seal, the Adélie penguin, the south polar skua, and in two species of Antarctic fish (Trematomus bernacchii and Chionodraco hamatus) from Terra Nova Bay, Antarctica. The results show a clear relation between PCB concentrations and trophic level, in the order fish < Adélie penguin < Weddell seal. The higher values found in the skua appear to be related to its migration to more contaminated lower latitudes. The data for the various PCB congeners were used to calculate toxic potential in the different animals. The 2,3,7,8-TCDD toxic equivalents of coplanar congeners were estimated by the “toxic equivalent factors” (TEFs) approach. The highest values of TEFs were found in the south polar skua and Weddell seal. Values in the other species were considerably lower.