Polychlorinated terphenyls (PCTs) are structurally similar to polychlorinated biphenyls (PCBs) and have been used in analogous applications. Aroclor 5432, a PCT formulation whose congeners contain predominantly two to five chlorines, was detected in sediments and oysters from a saltmarsh creek and an adjacent Chesapeake Bay tributary, Back River. Reports of the occurrence of Aroclor 5432 are virtually nonexistent, although sporadic reports of the more highly chlorinated PCT formulation Aroclor 5460 have been published. Capillary gas chromatography with electrolytic conductivity detection was used for quantitation. Identifications were confirmed by both electron ionization and negative chemical ionization mass spectrometry. Sediment concentrations detected were as high as 250000 μg/kg (dry-weight basis). Oysters collected from these areas contained up to 35000 μg/kg. This value is equivalent to 6300 μg/kg, on a wet-weight basis, and exceeds the applicable U.S. limit for PCBs in edible shellfish by more than a factor of 3. © 1990, American Chemical Society. All rights reserved.