The influence of sulfur and phosphors containing substances, hydroperoxide decomposers, on the kinetics of the consumption of two phenolic antioxidants in polypropylene (PP) was studied. The induction periods of PP autoxidation at 130degreesC were measured in the presence of inhibiting compositions that consisted of phenolic inhibitors and decomposers of hydroperoxide. The obtained results indicated that the influence of the hydroperoxide decomposer became significant when the concentration of the phenolic antioxidant became close to a critical value. It was shown also that the influence of the hydroperoxide decomposer significantly depended on the mechanism of the phenolic inhibitor transformation: first of all, on the nature of its transformation products. (C) 2003 Wiley Periodicals, Inc.