MECHANICAL or chemical treatment is usually required to prepare a surface for electron diffraction examination. This may lead to distortion of the structure which is undesirable, particularly when comparison with X-ray data is required. A surface farmed by solidification of a molten metal in vacuo may be regarded as probably the most satisiactory obtainable. In the present investigation the purest available copper was melted in an alundum boat in a fused silica tube which was connected to a Hyvac pump. The surface of the specimens was bright and smooth. Both electron diffraction and X-ray photographs were taken. Both gave sharp spots indicating the presence of large crystals, but whereas X-rays showed that the orientation of the crystals differed from specimen to specimen, electron diffraction showed spots from copper crystals orientated with either {111} or {100} planes parallel with the surface, the {111} orientation being most frequent. Twenty photographs gave similar results.