The dioxin receptor is the focus of current controversy regarding safe exposure levels for dioxin. Although the mechanisms are unclear, many of the toxic effects of dioxin have been linked to its receptor, leading to suggestions that most if not all of the toxic and carcinogenic effects of dioxin may be mediated by the dioxin receptor. If this is so, exposures to concentrations of dioxin well below the dissociation constant of dioxin from the receptor are unlikely to lead to toxicity, and standard methods for the extrapolation of dioxin's toxic and carcinogenic effects to lower doses would result in overestimation of the risks of exposure