The paper describes a fundamental investigation of the corrosion behaviour of Cu-Ni-Fe-Mn alloys, containing nominally 10% Ni and 30% Ni, in distilled water. The study involved exposure of specimens to distilled water (1.5-7 mu S/cm) at 20-80 degrees C with and without injected carbon dioxide. At 20 degrees C upon initial exposure to distilled water, the 10% Ni alloy exhibited somewhat active corrosion behaviour during anodic polarisation potentiodynamic scans but, after a few days＇ exposure, more-passive behaviour of both alloys was indicated with the 30% Ni material demonstrating better corrosion resistance than the lower-Ni alloy. However, at higher temperatures, the superiority of the 30% Ni alloy was less evident especially in the presence of dissolved carbon dioxide. Indeed, even a relatively short period of bubbling pure CO2 following a long period in distilled water, reduced the corrosion resistance of both alloys. Microscopic examination of specimens revealed susceptibility to pitting attack and, to a lesser extent, crevice corrosion after extended exposures at 20-80 degrees C.