One of the major challenges in the field of radiation biology is to correlate the results of biochemical studies with the process of DNA repair as it occurs in the living cell. The overall goal of this project is to develop better methods for visualizing DNA doublestrand breaks and double-strand break repair complexes in situ, in irradiated cells. Technologies are particularly needed to study repair complexes induced by low doses of radiation, where only one or a few breaks may be present.