Strontium-doped thermally pretreated NaCl crystals, X-irradiated at room temperature, were heated to 500°K for glow - curve measurements. The recorded glow curves show two definite peaks at 340 and 460°K. Study of the growth of these peaks with X-irradiation time indicates that the 460°K peak may be related to impurity - vacancy dipole in association with a negative ion vacancy situated in the dislocation region of the crystal.