The nature of the metal cation (Cu, Zn, Ni) on the oxidative degradation inhibition activity of their diethylthiocarbamate salt mixtures with amine- or phenyl-type anti-oxidants has been studied on cis -1,4-polyisoprene. The stabilizing effect by such mixtures has been found to depend not only on the components and their ratios in the mixture, but also on the evaluation method used to determine the activity (from the induction period prior to oxidation or the degradation rate of the polymer). The findings are well explained within the framework of the accepted mechanism of the inhibiting activity of diethyldithiocarbamic acid, including the reactions with peroxide radicals and the catalytic decomposition of hydroperoxides molecular products.