Xanthate interaction with pentlandite and pyrrhotite has been investigated using single and mixed mineral systems in the presence of sodium meta-bisulfite (MBS) and/or diethylenetriamine (DETA). Dixanthogen was identified as the main adsorption product on both minerals and its surface concentration was consistently higher on pentlandite than on pyrrhotite. Physical contact between the two minerals in suspension promoted dixanthogen formation on pentlandite at the expense of depressing its formation on pyrrhotite. DETA, MBS and DETA plus MBS reduced the dixanthogen adsorption on both minerals, with a decreasing effect from DETA plus MBS to DETA and finally MBS alone. For pentlandite in the mixed mineral system, DETA in combination with MBS reduced dixanthogen adsorption to a level similar to that in a single mineral system without depressants. The enhancement in dixanthogen formation on pentlandite by physical contact of the minerals is preserved on addition of depressants which reduce the absolute dixanthogen adsorption on pyrrhotite perhaps below a critical level for flotation.