Dioxins are one of the most toxic man-made compounds known and are persistent contaminants in the environment. The term dioxins generally refer to a family of related chemical compounds that include the chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans. Collectively, these groups of compounds belong to a class of compounds called Dioxin-Like Halogenated Aromatic Hydrocarbons (DL-HAH’s). These chemicals and their toxicity has been studied for more than 30 years and are known to accumulate in animals causing toxic effects. Birth defects, immunotoxicity, tumor production, changes in metabolism and even death have all been observed as a result of exposure to DL-HAH’s. The mechanism of action of these compounds has been extensively studied over the past twenty years. These compounds bind to an intracellular receptor called the aryl hydrocarbon receptor (Ah Receptor) and activate the receptor. The AhR itself was first reported in 1976 and dioxins were studied for many years before then. The DL-HAH: Ah receptor complex then travels to the nucleus of the cell and binds to specific sequences in the DNA called dioxin responsive elements (DRE). The binding of the DL-HAH:Ah receptor complexes to their specific DNA binding site in the nucleus (called Xenobiotic response elements (XRE’s)) stimulates expression of adjacent dioxin/Ah receptor-responsive gene, which lead to the toxic and biological effects of DL-HAH’s.