[en] Electron spin resonance spectra of free radicals formed in the radiolysis of benzene-2,1-diazoquinone-4-sulphonic acid in polycrystalline form were recorded. Two different radical species were found: the first one was stable at 77 K, whereas the second one was formed at higher temperatures. The thermal stability of the latter was investigated in the 20-100 deg C temperature range, and the kinetic parameters for the decomposition process were determined. An appropriate mechanism of radiolysis was proposed. (author)