Measurements of the thixotropic breakdown of structure with time of agitation were performed at different rates of shear on a number of pigment suspensions and on various oils in a rotational viscometer. The product of rate of breakdown in thixotropic structure and time of agitation at any rate of shear was found to be a constant for each material. It is called ``the time coefficient of thixotropic breakdown'' and is independent of the rate of shear, which is applied to agitate the sample. The time coefficient of thixotropic breakdown is measured in absolute units, having the dimensions of viscosity (dynes sec./cm2). The equilibrium time—the time necessary to break the thixotropic structure down to its minimum at a specified rate of shear—was also found to be independent of the rate of shear applied while agitating.