This is a review of a series of experiments on formation, annihilation, structure or behaviour of cascade defects byin-situobservation using a 400 kV heavy ion accelerator/200 kV electron microscope link facility at the University of Tokyo. Most of the results described here are obtained in gold. The experiments take advantage of the high mobility of interstitials in gold and of the strong effect of surface sinks on the thin foil specimens, which reveal vacancy properties rather distinctively. The temperature of thein-situobservations ranges from 120 to 800 K.