Freshwater mussels, Elliptio complanata were collected from a reference and pollutant-impacted pond on Cape Cod, MA. Glutathione-S-transferase (GST) activity was measured in gill, hepatopancreas and foot. In addition, content of seven heavy metals were measured in whole bodies. GST activity was significantly elevated in hepatopancreas and foot, as was whole body cadmium level in animals from the contaminated site suggesting that these animals have been exposed to organic and inorganic contaminants. Sodium dodecyl acrylamide gel electrophoresis (SDS-PAGE) analysis showed putative vitellogenins with molecular weight 180 and 205 kDa bands only in the ovary. In non-denatured gel electrophoresis ovarian extracts revealed two higher molecular weight bands at 550 and 700 kDa, which were reproductive stage specific. Western blotting of SDS-PAGE and non-denatured gels using the anti-scallop yolk-protein antibody confirmed the presence of cross-reacting bands of the same molecular weights in the ovary but not other tissues. Although several experiments involving steroid hormone exposure were done, no significant changes in vitellogenin protein levels were observed. However, using an anti-human ERβ antibody, ERβ positive bands were observed both in female foot, and the ovary. No cross reactivity with the antibody was observed in hepatopancreas. Additional studies are required to resolve questions of vitellogenin regulation and the role of (xeno)estrogens in bivalve molluscs.