Polycyclic aromatic hydrocarbon quinones (PAHQs) produced by combustion of gasoline exhibit two chemical characteristics; one is their electron transfer abilitiy, transferring electrons from reducing agents to molecular oxygen to generate reactive oxygen species (ROS) associated with oxidative stress and the other is their ability to arylate cellular proteins, resulting in the disruption of signal transduction pathways. This review summarizes toxicological and pharmacological significances of such envirnmental chemicals through redox cycling and covalent modification.