The annealing behaviour of GaN after implantation of 181Hf and 111In was studied using the perturbed angular correlation (PAC) technique. During annealing most Hf probes are built in on substitutional Ga sites and the level of lattice damage decreases with annealing temperature TA. In the case of In the results also show a good recovery of the crystal lattice. However a large variation of the quadrupole interaction frequency is observed indicating a considerable change in the local lattice geometry. The dependency of this variation on the implantation dose is investigated. The values derived for the electric field gradients at the probe sites are compared to values determined by NMR measurements.