Since 1980 there has been an accumulation of new information concerning DNA-damage-inducible processes in eukaryotic cells. It is clear that changes in the concentrations of activities of specific protein molecules play central roles in toxicological response of cells to chemical and radiation damage to DNA. Identification of inducible proteins may be crucial in helping to explain target organ toxicity and species differences. Detection of these proteins or their mRNA's in humans may be useful in assessing human exposure or cellular injury.