The interaction of cerussite and galena with hydrosulfide and aqueous amyl xanthate at pH 9.5 has been investigated through zeta potential measurements. Zeta potential results indicate that the hydrosulfide and xanthate anions chemisorb or participate in surface reactions at both the cerussite and galena/solution interfaces. Molecular lead xanthate appears to cover the surface of amyl xanthate-treated cerussite whereas chemisorbed xanthate cowers the surface of galena under the same conditions. Sulfidization of the mineral surface, which sets in only after sufficient sulfide is added to precipitate aqueous lead as lead sulfide, causes the zeta potential to drop sharply to highly negative values. The redox potential sensed by a Pt electrode remains almost constant at low reagent dosages, and becomes more negative once the hydrosulfide and amyl xanthate report to the solution. Excess sulfide in solution, an indication of oversulfidized mineral surfaces, lowers the redox potential and inhibits amyl xanthate adsorption. Redox potential measurements may aid in achieving an efficient sulfidization of cerussite and oxidized galena for optimum xanthate adsorption and therefore flotation.