Seed cakes from evening primrose (Oenothera biennis) and an ext. from walnut-shells (Juglans regia) were used as stabilizing agents for ethylene-propylene rubber. Both agents differed in compn. of polyphenols but showed an antioxidant activity measured as a capacity for free radical scavenging and redn. of Fe(3+) ions. The rubber vulcanizates were exposed to thermal, UV or climatic ageing. An advantageous effect of the antioxidants on the mech. properties of aged vulvanizates was obsd.