This paper describes findings from a research investigation on the erosion corrosion behaviour of the Cu/ 10Ni-base alloy, which is extensively used in desalination plant, together with a higher-strength Cu-Ni alloy. The behaviour of the alloys was investigated in 3.5% sodium chloride solution at 19 +/- 2 degrees C and in impinging-jet conditions of velocities 2.4-86 m/s. The investigation utilised gravimetric and electrochemical techniques together with surface profiling and microscopy. The influence of applied cathodic protection was also examined. Whilst the expected general trend of increasing attack with impinging velocity was observed, there was evidence that the relationship is rather complex. Moreover, the modes of deterioration of the alloys were found to involve mechanical and interactive mechanical/electrochemical components. The findings are discussed in terms of the detailed mechanisms of erosion corrosion and their relevance to the use of copper-nickel alloys in desalination plant.