Pyrite does not display self-induced flotability from mixtures with quartz except in acidic solutions. In the presence of galena and a metal complexing agent, however, pyrite can float strongly from ores and mineral mixtures in the absence of collector. Batch flotation tests have been used to study this behaviour from mixtures of galena, pyrite and quartz in moderately alkaline conditions. Evidence is presented that the flotation is brought about by the formation of a sulphur-based entity derived from galena which itself had been oxidised by ferric species originating from the pyrite. The hydrophobic entity reports as sulphur when leached with cyclohexane from the surfaces of floated minerals. The sequence of events which leads to pyrite flotation is described and a reaction path based on the transfer of sulphur as a soluble sulphide species from galena to pyrite is proposed. Some consequences of the influence of pyrite on the separation of valuable minerals from sulphide ores are discussed.