Seven Sumitomo alumina powders of different surface areas and particle size distributions were studied with a view to determining the optimum amount of dispersant (Darvan 821A) required to stabilise aqueous suspensions prepared from the powders. Th ree different techniques were used; sedimentation, particle sizing and acoustophoresis. Acoustophoresis proved to be the most accurate and quickest way of establishing the optimum amount. It was also shown that the optimum amount of dispersant (0.59 mg/m(2)) required to stabilise the different sized alumina powders was independent of the powder surface area/size. Sedimentation results demonstrated that the larger particles acted like hard spheres with thin double layers and gave a smaller relative sediment height than the small particles under the same conditions, i.e. volume fraction and electrolyte strength. This was because the small particles acted as soft spheres with thick double layers that resulted in the particles keeping far apart from one another and hence giving a larger sediment volume.