The effect of high strain on the oxidative stress relaxation of several natural rubber vulcanizates has been investigated. In the case of peroxide and CBS accelerated vulcanizates, the rate of stress relaxation increases with increasing strain, and this increase appears to be due to an increase in the rate of oxidation of the network. TMTD and MBT vulcanizates showed marked premature failure at high strains and no oxidative stress relaxation measurement could be made. It was found that the tensile strength of a TMTD vulcanizate was at least 20% higher in vacuum than in oxygen, due, it is believed, to stress-induced oxidative degradation at the tip of surface flaws in the rubber.