We evaluated the concentration and congener distribution of seven "target" polychlorinated biphenyls (PCBs) present in water collected in different aquaculture farms of the Mediterranean area, commercial feeds, and farmed seafood. PCBs were present in feed and in tissues of all the analysed organisms at levels ranging from 1.96 ng g(-1) to 124.00 ng g(-1) wet weight, and in 10.5% of the water samples, at levels from under detection limit to 33.0 ng l(-1) with total PCB concentrations significantly higher in samples from the Tyrrhenian Sea than the Adriatic Sea. PCB congener distribution in tissues resembled that of feed, suggesting that commercial feed is an important source of PCBs. The estrogenicity of organic extracts of the samples was also evaluated by using an in vitro yeast reporter assay. Estrogenic activity higher than 10% of the activity induced by 10 nM 17 beta-estradiol was observed in 20.0% of seafood samples and 15.8% of water samples. Seafood and water samples from the Tyrrhenian Sea were more frequently estrogenic than the Adriatic ones (16.45 versus 4.08%). A significant correlation of total PCB concentrations on biological activity was observed for sea bass and mussels from the Adriatic Sea (p < 0.045 and p < 0.04, respectively), and for sea bass of the Tyrrhenian Sea (p = 0.05). These results indicate the need of an integral approach in the exposure assessment to potential toxic compounds for human via food.