Diet and environmental exposures to aromatic and heterocyclic amines, and polycyclic aromatic hydrocarbons, are thought to be etiologic factors for breast cancer risk. In this study, we chose to quantify the major DNA adduct derived from one member of each of these classes of carcinogens in epithelial cell DNA isolated from human breast milk. Appreciable adducts were detected for each class, namely 2-amino-6-phenylimidazo[4,5-b]pyridine (PhIP), 4-aminobiphenyl (ABP) and benzo[a]pyrene. The effect of several metabolic genotypes on adduct levels were also investigated and higher PhIP and ABP adducts were associated with the rapid NAT2 and/or rapid NAT1 genotypes. The presence of ABP adducts was also significantly associated with the use of hair coloring products (OR=11.2, 95% CI=1.1-109.2) but not tobacco usage. These data indicate that women are exposed to several classes of dietary and environmental carcinogens and that metabolic genotype can be a susceptibility factor.