Friction experiments were conducted in vacuum with outgassed surfaces. Experiments were made with single and polycrystalline Al2O3, sliding on themselves and in contact with metals at a sliding velocity of 0.013 cm per second, at loads to 1500 gm, temperatures to 575 C and ambient pressures to 10−10mm Hg. These studies were made with a hemispherical or spherical rider sliding on the flat of a rotating disk. The results of the investigation indicate that (a) the friction characteristics of sapphire sliding on sapphire is highly anisotropic, (b) with metals sliding on sapphire, fracture in sapphire occurs while with polycrystalline Al2O3shear occurs in the metal, and (c) hexagonal metals exhibited lower friction co-efficients than cubic metals in contact with polycrystalline Al2O3.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis, Minnesota, October 18–20, 1966.