The radiolysis of iodobenzene labelled with125I has been investigated at liquid nitrogen and room temperatures, in the presence and absence of oxygen. After various storage times the samples were analyzed by gas chromatography, and benzene, vinyl iodide, biphenyl, and iodobiphenyl were detected. Biphenyl, benzene, and iodobiphenyl were found to be formed as a result of local radiolytic effect of Auger electrons of125I, and vinyl iodide was probably produced due to the decay effect of125I in labelled iodobenzene molecules. At the site of125I decay the Auger electrons are radiolytically effective within a spherical volume with diameter of about 30 A. Outside this sphere the energy absorbed by iodobenzene molecules is not high enough to produce any radiolytical damage.