The effects of ionizing and ultra-violet radiation on nucleic acids and proteins and their constituents are being studied. The modification of radiation damage in DNA by cancer chemotherapy agents of the intercalating and alkylating types is of interest, since such information may be useful in radiation therapy. The present report includes electron spin resonance (E.S.R.) studies of spintrapped radicals produced by the reaction of hydroxyl radicals and of hydrated electrons with constituents of proteins and nucleic acids.