Certain aryl compounds that have nitrogen substitutions on their ring structures are, following metabolic conversion to reactive derivatives, able to elicit toxic responses by virtue of their modifications of protein and nucleic acid. This group of compounds is often referred to as aromatic amines (AA), although from a structural perspective, compounds that can be converted metabolically to crucial AA derivatives are also capable of producing the same adverse biological effects. These effects include cellular death, mutagenic events and tumor induction. Importantly, in humans, AA can induce tumors in the urinary tract, and possibly other tissues. This contribution addresses the mechanisms by which AA are likely to produce these carcinogenic consequences.