Physical and chemical agents in the environment damage the DNA of humans, and pose a major threat to human health today, and to the genetic integrity of human populations. Although studies on isolated DNA in vitro, on prokaryotes, on mammalian cells in culture, and on laboratory animals have provided essential background information, it is now possible to study DNA damage and repair in human tissues directly. New techniques of high sensitivity, especially those not requiring radioactive labeling have made possible quantitation of DNA damage and repair, as well as detection of residual,...