This paper reports studies related to problems of vapour-side corrosion of copper/nickel alloys in multistage flash desalination plant. The main objective of the work was to obtain basic information and understanding of the corrosion behaviour of copper/nickel alloys in distilled water over a range of relevant environmental conditions. Some attention was also devoted to titanium and an austenitic stainless steel. The experiments were conducted in controlled laboratory conditions with assessment of corrosion behaviour mainly involving electrochemical monitoring. The results demonstrated a clear superiority of the Cu/30Ni alloy over Cu/10Ni material at ambient temperatures and also nonprotective behaviour of both alloys upon initial exposure to distilled water at 80 degreesC. In the time scales of the experiments (up to 15 days), no evidence was found that the presence of carbon dioxide at 80 degreesC made the water significantly more aggressive to the copper/nickel alloys. The superiority of the Cu/30Ni alloy over Cu/10Ni at lower temperatures did not appear to extend to the higher temperatures (80 degreesC) studied. Certainly at short exposure times, titanium and UNS S31603 stainless steel posses considerably superior corrosion resistance than the copper/nickel alloys over the entire range of conditions studied.