Determinations of the adsorption of sulfates at the ZrO2solution interface have been performed at constant ionic strength (10(-2) M KNO3) and at two different pH values (isotherm 1, pH 4.5; isotherm 2, pH 2.6). In both cases the adsorption isotherms presented a langmuirian shape; parameters describing the adsorption were obtained by processing data in the reciprocal Langmuir coordinates. The degree of packing of the adsorbed molecules and the nature of the forces supporting the adsorption are also discussed on the basis of literature results.