The overall objective of this project is to develop a method for monitoring DNA damage. Damage to DNA in the form of double and single strand breaks will be assessed by fluorescent, in situ nick translation, employing suspensions of lymphoid cells and a DNA synthesizing system containing E. coli DNA polymerase I. Ionizing radiation will be employed to verify the efficacy of the methodology. We will also determine the feasibility of this technology to i)study DNA repair, and ii) monitor the radioprotective effects of low, inducing doses of ionizing radiation. Human cell lines with various genotypic configurations of the p53 gene will be employed to study the effect of radiation on DNA damage and repair using the nick translation technique.