The corrosion of the pure metals aluminium, cobalt, copper, chromium, molybdenum, nickel, and titanium and of a cobalt-chromium molybdenum casting alloy has been studied in buffered saline with and without the presence of the proteins serum albumin and fibrinogen. The corrosion of aluminium and titanium was unaffected by the protein. The corrosion rates of chromium and nickel showed a slight increase, while cobalt and copper dissolved to a very much greater extent in the presence of protein. However, with molybdenum the corrosion was inhibited by protein.