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Abstract: Marine mammals respond to the presence of polycyclic and planar halogenated aromatic hydrocarbons (PAH or PHAH) with the induced expression in endothelium of cytochrome P4501A1, regulated through the aryl hydrocarbon receptor (AHR) transcription factor. Physiological responses in other animals, such as edema and inflammation indicate that the endothelium may be compromised by exposure to AHR agonists, which are ubiquitous in the marine environment. In other mammals and fish the cellular and molecular consequences of exposure to AHR agonists have been elucidated in cultured endothelial cells. We have cultured and characterized cetacean endothelial cells (EC) and used them in induction studies. Endothelial cells were cultured from the lung and kidney of the bottlenose dolphin, Tursiops truncates, and exposed to the AHR agonists β-naphthoflavone (βNF) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). βNF (1–3μM) induced significant increases in CYP1A1 (O-deethylation of 7-ethoxyresorufin to resorufin; EROD) activity to 3.6 and 0.92pmol/mg/min in lung and kidney EC, respectively. TCDD was more potent than βNF, and more efficacious, with maximum induction of CYP1A1 activity of 10.1 and 15.2pmol/mg/min in lung and kidney EC at 3–10nM TCDD. The differential response indicates that the lung and kidney endothelial cells in culture retain the ability to respond in a selective manner to specific stimuli. Both the molecular mechanisms of induction and the physiological consequences, especially in the vasculature, of toxicant exposure can be studied in this system. [Copyright &y& Elsevier]