Often, blends of two immiscible polymers have a morphology with one component building a matrix in which spherical inclusions of the other component are embedded. The theological response of such blends contains an elastic contribution which can be attributed to the form relaxation of the inclusions. This process has a characteristic relaxation time which is proportional to the radius of the inclusions divided by the interfacial tension between the blends’ components. Thus a distribution of radii leads to a distribution of relaxation times. It is shown that theological data together with an emulsion model can be used to determine the volume weighted sphere-size distribution up to a scaling depending on the interfacial tension. The procedure is applied to data of four PMMA/PS blends and the results are compared with the corresponding distributions obtained from transmission electron microscopy (TEM). If the concentration of the spherical inclusions is small, both results are in excellent agreement. For larger concentrations, deviations between the results from theology and TEM are observed.