To extend our studies on the effects of ultraviolet (UV) radiation and X-rays upon the nucleic acids in vitro and in vivo; to elucidate the biochemical bases and genetic control of the multiple pathways of the repair of radiation damage in bacterial and mammalian cells; to study the interaction and/or overlap of these different repair pathways, their possible induction by radiation, their selective inhibition by drugs, and to determine which pathways are error free and which are error prone (i.e., mutagenic). These studies will contribute to a better understanding of the molecular biology of DNA repair, of the mechanism of mutagenesis (and carcinogenesis), and may possibly indicate ways in which radiation can be even more effectively used in the treatment of cancer (e.g. by the selective chemical inhibition of repair).