The effect of galvanic interactions between chalcopyrite and pyrite on their collectorless flotation behaviour have been studied. Cyclic voltammetry and microflotation tests were carried out to identify the reaction products and flotation behaviour of sulphide minerals after different types of galvanic interactions. It was found that galvanic interactions between a noble mineral (pyrite) and an active mineral (chalcopyrite) significantly affected the floatability of both minerals. The results of flotation tests carried out with different mineral-mineral combinations showed that depression of chalcopyrite and activation of pyrite depends to a great extent on their magnitude in the mixture. The dissolution behaviour of both minerals in an aqueous solution was also studied and probable electrochemical reaction mechanisms relating to activation of pyrite by copper ions were discussed. (C) 1997 Elsevier Science B.V.