Abstract: An NMR test method is provided for determining the homogeneity of dispersion of a filler substance such as carbon black in an elastomer composition such as a rubber, either on an arbitrary scale or by reference to a standard dispersion of optimum homogeneity which is given the value 1.0 on a linear scale. The method involves measuring the intensity of the short component and the total intensity of the proton free induction decay, of a sample of the dispersion deriving the ratio P.sub.t of said intensities, and optionally deriving a second similar ratio P.sub.s from the standard dispersion to permit a value P.sub.t /P.sub.s on said linear scale to be derived.