Electrochemically thinned and polished discs of high purity aluminium were irradiated with 60 keV argon ions and were subsequently examined in an energy analysing electron microscope of the Mollenstedt type. Image features believed to arise from small argon bubbles in the aluminium matrix and argon “blisters” at the aluminium/oxide interface were observed. The electron energy loss spectrum from the bubbles is in agreement with Natta's theory.