NO-induced decomposition of hydroperoxides in solid polypropylene and cumyl hydroperoxide, dissolved in n-decane, at 25 degreesC was studied. Analysis of kinetic regularities of hydroperoxide decomposition and nitroxide radical accumulation leads to the conclusion that both in solids and in solutions these reactions have the autoaccelerated character. The induction periods are determined by trace amounts of impurities (probably of higher nitrogen oxides). The maximum rate of the process depends on the NO pressure. The possible reaction mechanisms are supposed, and the key role is assigned to the formed nitrosocompounds.