Major objectives of this program are elucidation of mechanisms for repair of radiation injury by examination of factors modifying repair; delineation of quantitative dose-response relationships for various manifestations of noncytokinetic injury; and comparison of repair activities between proliferative and postmitotic tissues. Insect material is the experimental material exploited: Pupariation delay and puparial elongation after irradiation of fly larvae, a hyperacute lethal syndrome in adult beetles exposed to very high radiation doses, and increased longevity of adult insects exposed tissue; acute (5-week) mortality of irradiated beetles is clearly the result of damage to small population of proliferative cells of the midgut. Hyperthermia is the major modifier of repair studied; injury by high LET radiations and by DNA-damaging chemicals are also examined.