It is shown that in α-copper-aluminium alloys interstitials are able to change sites with the copper and aluminium atoms by diffusion. The activation energy for migration of interstitials could be determined to be 0.82 eV. In a well annealed specimen the interstitials and vacancies annihilate nearly exclusively by pair recombination. The production rate of free interstitials is found to be slightly larger than that of free vacancies during an irradiation with fast neutrons. The excess interstitials, which are supposed to originate from depleted zones, form clusters acting as sinks, at which essentially interstitials anneal out. Due to these sinks another steady state equilibrium („fixed vacancy case“) among point defects and sinks is achieved by repeated irradiations.