HETEROCYCLIC HYDRAZINES AND LACTAMS ARE PROVIDED WHICH ARE USEFUL IN THE ENHANCEMENT OF THE RESISTANCE OF OLEFIN POLYMERS TO COPPER-CATALYZED OXIDATIVE DETERIORATION. IN ADDITION, THERE ARE ALSO PROVIDED STABILIZER COMPOSITIONS CONSISTING ESSENTIALLY OF AT LEAST ONE OLEFIN POLYMER STABILIZER AND HETEROCYCLIC HYDRAZINES OR LACTAMS; OLEFIN POLYMER COMPOSITIONS, SUCH AS PROPYLENE POLYMER COMPOSITIONS, CONTAINING HETEROCYCLIC HYDRAZINES OR LACTAMS; AND A PROCESS FOR ENHANCING THE RESISTANCE OF OLEFIN POLYMERS TO COPPER-CATALYZED DEGRADATION BY INCORPORATION OF SUCH COMPOUNDS OR OF SUCH STABILIZER COMPOSITIONS.