Although under normal conditions only the crystallization behavior of PE on oriented IPP substrates can be studied due to the higher melting point of iPP, the faster crystallization rate of a molten, oriented HDPE film compared to a nonoriented IPP layer was used to study the crystallization of iPP on the oriented HDPE film by means of transmission electron microscopy (TEM) and electron diffraction (ED). Besides the known epitaxial relationship of HDPE/iPP with their chains 50 degrees apart, two new orientation relationships with (a) chains of both polymers parallel and (hk0)(iPP) in contact with the HDPE substrate, and (b) the a-axis of iPP crystals parallel to the chain direction of HDPE but (001)(iPP) in contact with the HDPE substrate were observed. Both orientations are assumed as graphoepitaxy.