PAH containing a peripherally fused cyclopenta ring are genotoxically active in Salmonella and mammalian cells and have been identified in combustion emissions. Since the cyclopenta ring is predicted to be susceptible to electrophilic attack, nitrosubstituted cyclopenta-fused PAH may be formed in the presence of NO(x), particularly in diesel exhaust, and hence be present in the environment. Nitro derivatives of cyclopenta (cd) pyrene and the cyclopenta-fused benzanthracene isomers were prepared by reaction of the PAH with dinitrogen tetroxide. The purifed products were characterized by mass spectroscopy, (1)H NMR, UV-vis and HPLC. In all cases, nitro substitution occurred on the cyclopenta ring in accord with expectation. Preliminary assay in S. typhimurium indicates that 4-nitro-cyclopenta(cd)pyrene is mutagenically active without exogenous metabolic activation in nitroreductase-competent strains. The results of the study have allowed us to test the hypothesis and will aid in development of structure-activity relationships of nitroPAH.