The ionic thermocurrent of NaI doped with small amounts of calcium has been studied with the usual ITC technique. Three bands are observed: the high-temperature band (225 K) is due to the dissociation of aggregated dipoles whereas the origin of the lowtemperature band (~170 K) is still unknown. The study of the main band with a maximum at 192.5 Kleads toanactivation enthalpyof0.59 eVandan activationentropy(2.4 % 0.8) K. These activation parameters might correspond to NN-+ NN jumps of a bound cation vacancy around the divalent impurity.