The following section gives an overview of approaches to carcinogen risk assessment for PAHs and presents a consideration of how each approach could be adapted to high potency PAHs. There are several problems that complicate the carcinogenic risk assess-ment of the complex mixture of PAHs and other com-pounds to which human exposure may occur. Although the carcinogenic risk of several PAH mixtures in hu-mans has been estimated from epidemiological studies, it is not known to what extent the PAH fraction of the mixture, as opposed to other chemicals and particulate matter, contributed to carcinogenicity (WHO, 1998). No data are available to assess the carcinogenic potency of individual PAHs in humans, so animal data must be used to assess individual PAHs and results extrapolated to the low doses to which humans are exposed. However, only a small percentage of the environmentally relevant PAHs has been investigated for carcinogenicity in animals (WHO, 1998). Carcinogenic potency estimations are considered valuable tools in risk management (Roberts et al., 2001). The basis for the assessment of PAH potency and whether the mixture is expressed in terms of the total mass of extractable material or as units of a surrogate such as B[a]P are also important. The use of a surrogate assumes that it is predictive of the toxicity of the mixture.