Pyrogenically prepared, surface modified aluminum oxide, having the following physical chemical properties: TABLE-US-00001 Surface area [m.sup.2/g] 50 to 150 Tamped density [g/L] 25 to 130 Drying loss [%] less than 5 Loss on ignition [%] 0.1 to 15 C content [%] 0.1 to 15 pH value 3 to 9 is prepared by treating pyrogenically prepared aluminum oxide with a surface modifying agent.