Reactions of SO3.- radicals with complexes of Ni(II and I) and Cu(II and I) were investigated under anaerobic conditions. Reactions of CuCR+, Cu(TIM)(+), and Ni(Me-6[14]dieneN(4))+ with SO3.- radicals were investigated by time-resolved spectroscopy. The kinetics of the processes is in accordance with an outer-sphere electron-transfer mechanism. Intermediates with a ligand-radical nature were observed in SO3.- reactions with Cu(2,9-dimethyl-1, 10-phenanthroline)(2)(+), Cu(Me-6[14]dieneN(4))(2+), NiCR2+, or NiCRH42+. Two products were isolated in the reaction of NiCR2+ with SO3.- radicals, one product with a sulfonated macrocycle and the other product with one additional double bond in the macrocycle. These products confirmed the attack of the ligand by SO3.- radicals and the formation of intermediates with a ligand-radical nature. A mechanism based on the oxidative addition of SO3.- radicals to the ligand accounts also for the kinetics of product formation.