Interaction of polypropylene hydroperoxides with nitric oxide at 25 degrees C was studied. The kinetics of the hydroperoxide decomposition abides a complex autoaccelerated pattern. The induction period of decomposition is determined by the trace amounts of impurities, probably, higher nitrogen oxides. The maximum rate of the process depends on the nitric oxide pressure. ESR data revealed the formation of macromolecular nitroxyl radicals, which is an evidence that free-radical stages are involved in the decomposition of hydroperoxides in the NO atmosphere. The possible reaction mechanisms are discussed.