Series of rhenium catalysts were prepared by equilibrium adsorption on unmodified alumina and alumina containing F and Mg additives. The uptake of perrhenate on alumina was dependent on the pH and the concentration of nitrate in the impregnation solution. Uptake of perrhenate at pH 6.5 on F modified alumina decreased with increasing F loading; for Mg-modified aluminas, perrhenate uptake at pH 9.3 increased with increasing Mg content. A correlation was observed between perrhenate uptake and the isoelectric point (IEP) of the modified supports. These data are interpreted on the basis of electrostatic attractions which occur between perrhenate ions in solution and alumina surfaces. Competition between nitrate and perrhenate for adsorption sites satisfactorily accounts for the effect of nitrate on perrhenate adsorption.