Exposure to polycyclic aromatic hydrocarbons (PAHs) and their nitro-substituted derivatives (nitro-PAHs), products of incomplete combustion, is widespread. This is of concern because individual PAHs and PAH-containing mixtures cause tumors in animals and they are suspected to contribute to human cancer. To asses their carcinogenic potential in humans, biomarkers of PAH exposure that measure the internal dose or the effective dose need to be developed. Dr. Karam El-Bayoumy and his associates at the American Health Foundation set out to develop methods for measuring DNA and protein adducts formed in animals after exposure to nitro-PAH derivatives. To begin the development process, they treated laboratory rats with two important PAHs: 1-nitropyrene, which is the most abundant nitro-PAH, and the highly mutagenic and tumorigenic 1,6-dinitropyrene. At intervals, tissue and blood samples were taken from the treated rats and examined for the presence of DNA and protein adducts. In addition, Dr. El-Bayoumy determined the structures of several of these adducts and began to investigate the mechanisms involved in their formation.