The dielectric method applied in the frequency range 0.4-110 MHz is well adapted to analyze the competition between amylxanthate and nickel or cobalt hydroxide used as depressor during the flotation of galena at pH 10.0. Nickel hydroxide is able to depress galena no matter the sequence of reagent addition. Cobalt hydroxide is less efficient. The co-adsorption of the collector and the depressor on PbS is confirmed by spectrophotometry and elecrokinetics.