One of the most vital of the cellular defenses against pollution is an 'antioxidant armanentarium' which consists of oxidant scavenging molecules such as vitamin E, glutathione, vitamin C, and uric acid as well as a number of enzymes (superoxide dismutase, semidehydroascorbate reductase, catalase, GSH synthetase, GSH peroxidase, GSH reductase, and GSH transferase) and appears to function in keeping oxidant forces under control. Pollutants can upset the oxidant/antioxidant balance of cells by inhibiting vital enzymes, by reacting with oxidant scavengers, or by forming free radical intermediates which initiate uncontrolled tissue reactions with molecular oxygen. The book chapter reviews possible interactions between pollutants and the oxidant/antioxidant balance.