The aim of the work presented was to study the effect of the annealing temperature upon the formation of second phases in the NaCl matrix by using the optical absorption and ionic thermocurrent measurements. The 60, 125, 235 and 350°C isotherms were followed mainly for crystals containing 120 mole ppm of divalent europium. The three lower annealing temperatures result in a decay of the impurity-vacancy dipole concentration up to ∼5% of the initial value being accompanied by the growth of metastable phases with their characteristic optical absorption spectra previously observed for as received samples, only. At 350°C the decay of the impurity-vacancy dipole concentration reaches ∼20% of the initial value, and the newly appeared optical absorption spectrum has been ascribed to the stable EuCl2 precipitates with the PbCl2 type of structure.