It has been shown that the thermal decomposition of 4-hydroperoxy-4-methyl-2, 6-ditert-butylcyclohexadien-2, 5-one is accompanied by the rupture of the C-O bond in the COOH group, with the formation of 2, 6-ditert-butyl-4-methylphenoxyl radicals. On the basis of the electronic paramagnetic resonance spectra, it has been found that transfer of hydrogen occurs from the diphenylamine molecule and those of sterically hindered phenols to the radicals of 2, 6-ditert-butyl-4-methylphenoxyl radicals formed by the decomposition of the hydroperoxide.