Small-angle X-ray scattering (SAXS) data have been used to deduce the localization of organic additives in the bulk of isotactic polypropylene (iPP). The results have shown that changes in the thickness of a transition layer are not directly connected with the introduction of additives but with the content of the hexagonal B-form. This leads to the conclusion that the additives are placed in the amorphous phase in spite of their crucial influence on the formation of the crystalline phase of iPP.