The adsorption of stearic acid and bis(2-ethylhexyl) phosphate, from toluene and THF solutions, on magnetic iron pigments (MP) was examined, Adsorption isotherms as well as the concomitant variations of surface electrical (zeta) potential were determined. The formation of electrical surface charges is explained by charge transfer processes between the solvents, the adsorbates, and MP. An adsorption competition is evidenced when contacting MP with the adsorbates using C-14-labeled stearic acid.