Biofouling and corrosion products on 70/30 cupronickel exposed to polluted seawater were studied by SEM with EDAX analysis. Layers of corrosion products containing dissimilar levels of sulphide, iron, copper and nickel were detected. An outer porous layer covered by a biofilm was present in all samples. Only a few genera of diatoms and protozoa could be found in the biofilm. Biofilm establishment on cupronickel was delayed compared with other more inert materials previously assayed. Electrochemical measurements showed that sulphide ions affect cupronickel passivity, interfering in the formation of the outer passive layers.