Four non-ortho-, eight mono-ortho-, and two di-ortho-chlorinated congeners have been determined in fresh water and salt water mussels, fish, snapping turtles, mallard, seals, and in human milk and adipose tissue. The planar PCB congeners are separated from the remainder of PCBs by activated carbon chromatography or HPLC on porous graphitic carbon followed by gas chromatography with electron capture detection. PCB toxic equivalency factors (TEFs) recommended by WHO [1] for 3 non-ortho, 8 mono-ortho, and 2 di-ortho PCBs and a TEF for congener 81 suggested by Harris et al. [2] were used for calculation of the contribution to dioxin-like toxicity to each life form. In all the biota examined, PCB congener IUPAC number 126 was the major contributor to PCB toxic equivalents. Congeners IUPAC number 118, 114, 105, 156, 157, 77, 81, and 170 also contributed significantly to PCB toxic equivalents. The ability to separate out planar PCBs from the majority of PCBs has allowed the use of TCDD toxicity equivalence to compare the relative dioxin-like potency of PCB residues in various species from different locations.