[en] Recent advances in the study of point defects and small defect clusters by nuclear methods are reviewed. Suitable radioactive atoms which fulfill the requirements of the perturbed angular correlation (PAC) or Moessbauer (ME) technique are implanted into solids, where they are used as microscopic probes to investigate their immediate surrounding. Trapping, detrapping or annealing of defects is reflected by chances of the hyperfine interaction between the nuclear moments of the probe atoms and the electromagnetic fields of the defects, while the interaction itself allows the distinct recocgnition of different defects and can provide detailed information about their structural properties. Experimental data on interstitials, vacancies and clusters in fcc-metals will be quoted as illustrations of the scope of information which can be achieved by hyperfine interaction studies. (orig.)