Gamma-irradiated potassium hydroquinone monosulfonate (PHM) single crystals were investigated between 125 and 300 K using the electron paramagnetic resonance (EPR) technique. Between 125 and 300 K no changes in the spectra have taken place. The spectra were found to be temperature independent. The investigation of EPR spectra of irradiated single crystals of PHM showed the presence of two PHM anion radicals. The g values of the radiation damage centers observed in the PHM single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained.