This volume studies the risk to the environment and human health posed by nitroPAHS. Data on the in vivo genotoxicity of nitroPAHs are available for 15 nitroPAHs. All nitroPAHs that gave positive results in vivo were also positive in vitro. Four nitroPAHs that were positive in in vitro genotoxicity tests revealed inconsistent or inconclusive genotoxicity (2-nitronaphthalene, 5-nitroacenaphthene and 3-nitrofluoranthene) or negative genotoxicity (2,7-dinitrofluorene; limited validity) results in vivo. There are no reports on the effects of individual nitroPAHs on humans. As would be expected, since nitroPAHs occur in complex mixtures in the atmosphere and exhaust, the exact contribution of nitroPAHs to the adverse health consequences of exposure to polluted atmospheres and to exhaust cannot be elucidated.