In recent decades, a great deal of emphasis has been placed on evaluating the toxic potency of dioxin in different environmental samples. The commonly named dioxin-like compounds (DLCs), such as polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs), were studied to determine their relative toxic potency. Recently, some studies have indicated that another group of contaminants, the polycyclic aromatic hydrocarbons (PAHs), can dominate estimates of toxic equivalent quantity (TEQ) for samples containing PAHs and DLCs. Other emerging contaminants, such as brominated flame retardants (BFRs), especially polybrominated diphenyl ethers (PBDEs), also exhibit dioxin-like activities. The knowledge of the relative contribution of each contaminant to the total dioxin-like activity associated with environmental samples could aid in identifying the most important contributory pollutants. in this paper, an overview of current data for these estimates is presented. (C) 2003 Elsevier Ltd. All rights reserved.