A new suspension-based rheological method was applied to study experimentally the crystallization of a nucleating agent (NA) filled isotactic polypropylene. This method allows for determination of point-nucleation densities where other methods fail. For example, optical microscopy can fail because nucleation densities become too high to count (nucleated materials) or crystallites are not well visible (colored materials) while DSC doesn’t work when the effect of flow needed to be studied. Both quiescent and mild-shear induced crystallizations were investigated. The results show that addition of nucleating agent increases nucleation density up to 6 decades for quiescent crystallization. The effect of shear on crystallization in the presence of NA was assessed and it is demonstrated that, at least for this system, the effectiveness of shear is much less then the effect of the nucleating agent.