A culture gill epithelium from seawater-adapted tilapia (Oreochromis niloticus) was developed for testing PAHs and dioxin-like contaminants in seawater. The epithelia consists two to three layers of epithelial cells incorporating both pavement cells and mitochondria-rich cells (MRCs). Polarity and a stable transepithelial resistance (TER) were maintained, and closely resembled those in fish gills in vivo. The tightness (integrity) of the epithelia remained unchanged upon exposure to benzo[a]pyrene (B[a]P), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3,3',4,4',5-pentachlorobiphenyl (PCB#126), while a concentration-dependent response of EROD activity in the epithelia was induced within 18-24 h when the apical side was exposed to these toxicants. The 24 h EC50 of EROD activity was 2.77x10(-7) M for PCB#126, 1.85x10(-7) M for B[a]P and 7.38x10(-10) M for TCDD, showing that the preparation was not only sensitive to PAHs and dioxin-like compounds, but also able to produce inductive potency of AhR agonists that generally agreed with those derived from other established in vitro and in vivo systems. The results suggest that the cultured gill epithelia from seawater-adapted tilapia may serve as a simple, rapid and cost-effective tool for assessing exposure and potential effects of toxicants in marine waters.