Isobutyl xanthate interaction with pentlandite and pyrrhorite has been investigated in the case of single minerals, minerals sharing the same solution and minerals in physical contact using FTIR-ATR spectroscopy and open circuit potential measurements, The FTIR-ATR spectra showed that dixanthogen was the main adsorption product on both minerals. For minerals sharing the same solution, dixanthogen adsorption on pentlandite was increased compared to pentlandite alone, while in the case of pyrrhotite, the situation was reversed, Direct contact of the minerals caused this effect to become even more pronounced. Open circuit potential measurements showed that pentlandite has a higher mixed potential than pyrrhotite. In the presence of xanthate however, the order was reversed. A mixed potential model was used to explain the interaction between minerals. At the mixed potential of the mixed mineral system, the anodic reaction (xanthate oxidation to dixanthogen) occurred preferentially on the pentlandite and the cathodic reaction (reduction of oxygen to hydroxyl ion) occurred on the pyrrhotite. Physical contact, by inducing galvanic interactions, further promoted the effect. Some implications in flotation are discussed.