The effect of dispersant concentration on the rheological behavior of suspensions of Sub-micron aluminum oxide particles in either water or dodecane was studied using a double concentric cylinder rheometer. In the electrosterically stabilized aqueous system, the suspensions underwent a sharp transition from coagulated to dispersed as the concentration of the dispersant, ammonium poly(methacrylate)l, was increased. In the sterically stabilized dodecane system, as the concentration of the dispersant, 12-hydroxy stearic acid ester, was increased, the initially coagulated suspensions became highly thtxotropic at concentrations less than that needed for stability. The difference in behavior between these two systems is caused by the way that the interparticle forces are affected by the concentration of dispersant for the two types of stabilization mechanisms. The technique of inducing thixotropy by control of the dispersant concentration has certain advantages including wide applicability and not requiring special additives.