Toxic Equivalency Factors (TEFs) are components of a global toxicity index (the Toxic Equivalent Quantity-TEQ) that facilitates the risk assessment of complex PAH and HPAH mixtures. They are based on the structural similarities between congeners with a common mechanism of action (binding to the Ah receptor). Many aspects remain uncertain, however. Differences between species and between tissues in their response to these pollutants may significant affect the TEF values. Another source of uncertainty is our lack of knowledge about whether interactions between congeners have an additive effect (synergy or antagonism). In this study, we used various TEF values reported in the literature and found that they may significantly affect the estimates of the general population's food exposure (by a factor of 0.2 to 2.5). Consequently, they affect regulatory decision-making as well. Despite these flaws the TEF concept remains empirically very useful for risk assessment purposes.