Zeta potential determinations have been used to study the oxidation of galena surfaces. The galena samples have been conditioned in aqueous solution at several pH values with various gases and for different amounts of time. A mechanism involving the dissolution of lead ions followed by their readsorption as lead hydroxide ions or colloidal particles has been proposed to account for the changes in zeta potential occurring during surface oxidation. The Gouy-Chapman-Stern double layer model has been used to calculate the zeta potential as a function of pH. The effect of sodium sulfide addition has also been investigated. To confirm this mechanism of oxidation, the adsorption of lead nitrate on quartz has been studied.