The isothermal degradation of ethylene-propylene elastomers, ethylene-propylene rubber and ethylene-propylene-diene terpolymer, in four NaCl aqueous solutions (0%, 0.1%, 1.0% and 10%) was investigated. The film specimens were examined by i.r. spectroscopy to detect the evolution of oxygenated group content. It was shown that the lower the salt concentration, the more oxidative damage takes place in the polymer. There is a large discrepancy between the carbonyl and hydroxyl formation rates of these two materials. The ethylene-propylene copolymer is more oxidatively stable than its corresponding terpolymer.