Electron spin resonance spectroscopy was used to study the radiation induced paramagnetic centres in the polycrystalline CaSO 4 :Dy phosphor. Three dose-dependent signals were detected whose amplitude can be used for dosimetry in the (5-2000) Gy dose range. SO - 3 , SO - 4 and Ca-vacancy centres were regarded as responsible for the signals observed. Step annealing measurements suggest a connection between these centres and some thermoluminescent glow peaks.