The accumulation of a group of non-and mono-ortho (coplanar) PCB congeners in aquatic food webs is of special interest due to their dioxin-like toxicities. Furthermore, higher octanol-water partition coefficients than homologs with greater ortho-substitution suggest the potential for selective accumulation of the coplanar congeners. We quantified 47 PCB congeners containing 0-3 ortho-chlorines from six homolog groups in sediments, plankton, and fish from Green Bay, WI, using conventional and multidimensional gas chromatography with electron capture detection. Of the congeners exhibiting dioxin-like toxicity, the only nonortho-substituted congener quantifiable in any of the matrices was IUPAC 77, but all of the toxic mono-ortho-substituted congeners were detected and quantified. Penta-, hexa-, and heptachloro congeners were enriched relative to other congeners in sediments and fish located more distant from the main source of the bay, whereas trichloro congeners were depleted. The same homolog groups also became more enriched as PCBs moved to higher levels in the ecosystem from sediment to plankton to fish, while trichloro congeners were depleted. Enrichment patterns of the most toxic (dioxin-like) congeners were also influenced mainly by total chlorine substitution; the degree of orthosubstitution did not systematically affect accumulation in plankton and fish.