RNA oxidation is Important in the etiology of disease and as a tool for studying the Structure and folding kinetics of this biopolyrner. Nucleobase radicals are the rna,jor family of reactive intermediates produced in RNA exposed to diffusible species Such as hydroxyl radical. The nucleobase radicals are believed to produce direct strand breaks by abstracting hydrogen atoms from their own and neighboring ribose rings. By independently generating the formal C5 hydrogen atom addition product of uridine in RNA, we provide the first chemical characterization of the pathway for direct strand scission from an RNA nucleobase radical. The process is more efficient under anaerobic conditions. The preference for strand scission in double-stranded RNA over single-stranded RNA suggests that this chemistry may be useful for analyzing the secondary structure of RNA in hydroxyl radical cleavage experiments if they are carried out under anaerobic conditions.