Abstract The reactions of O 2CH 3 radicals with Cu II(glycine) 2 and Cu II(GGG), GGG = glycylglycylglycine, in aqueous solutions were studied. The results demonstrate that the peroxyl radicals oxidize the copper complexes forming relatively stable intermediates of the type L mCu III-OOCH 3. These intermediates decompose via oxidation of the ligands glycine and GGG, respectively. Substituents on the alkyl of the peroxyl radical affect somewhat the kinetics of reaction but not the mechanism of oxidation. It is suggested that analogous reactions are probably contributing to the radical-induced deleterious biological processes.