AFM force measurements were carried out between a silica colloid sphere and an alumina flat crystal over a wide pH range and in both 1 x 10(-4) and 1 x 10(-3) M KNO3 aqueous solutions. Microelectrophoresis and streaming potential experiments were performed on the silica colloid sample and the alumina plate, respectively. The potentials measured by the different techniques were in very good agreement. The results clearly indicate that AFM force measurements can be used to accurately determine diffuse layer potentials of metal oxide materials under these solution conditions.