[en] The effects of various metal ions (Cd²⁺ , Co²⁺, Ni²⁺, Cu²⁺, and Cr³⁺), present at a concentration of 1 metal ion per 100 nucleotides, on the formation of carbon radicals at 77 and at 298⁰K, on the production of phosphomonoester groups, and on hydrogen transfer in γ-irradiated DNA in the solid state in vacuo were investi gated. Those metal ions that decrease the radical yield at 77 and 298⁰K (as measured by electron spin resonance) were also effective in decreasing the formation of strand breaks and the transfer of hydrogen from exchangeable to carbon-bound sites. From ESR studies of cupric-DNA complexes, it was inferred that cupric ions compete with the bases in DNA for electrons produced by γ radiation, thus preventing the formation of anionic radicals at 77⁰K which are precursors of the stable neutral radicals observed at room temperature. (U.S.)