The spherulitic morphology of semicrystalline polymers can be influenced by nucleating agents. With high concentrations of such agents a morphology results which consists of small spherulites. This effect is used, for example, to increase the optical transparency of films or to increase the toughness [1]. A very different nucleating effect occurs in the row nucleation. In this case certain constituents of a polymer, for example, the highest molecular weight fraction or a polymer of higher density added by co-crystallization from xylene are oriented by the special processing conditions and crystallize to produce fibrous crystals which then serve as backbones for the so-called shish-kebab morphology [2]. This morphology exhibits high mechanical moduli. Most nucleating agents are unfortunately nonpolymeric substances with very different chemical and physical properties with respect to the polymer. To overcome this disadvantage work is being carried out to produce nuclefiting agents without these disadvantages by modification of the basic polymer. So electron beam treated polypropylene acts as a suitable nucleant of the unmodified polymer [3]. During our search for a nucleating agent for low density polyethylene (LDPE) we found that high density polyethylene (HDPE) is very succesful for that purpose [4]. This nucleant produced from the same monomeric unit as the polymer to be nucleated is not only interesting for its very similar chemical and physical properties but it can be used to direct the morphology of LDPE regardless of the size of the spherulites. It is also possible to generate a modified shish-kebab structure with a "macroscopic" core of high density polyethylene surrounded by a LDPE matrix or a transcrystalline morphology in LDPE due to the high nucleation density of the HDPE surfaces in contact with LDPE. This letter deals with the principle of the PE-PE nucleation and some basic results. More detailed results will be published elsewhere. The low and high density polyethylenes used are large scale technical products. Both were used as powder, film or as massive pieces (injection moulded test bars) depending on the problem of investigation. The crystallite melting points are in the order of 403 K (HDPE) and 378 K (LDPE). In some cases the HDPE powder was purified by dissolving it in xylene (100 ° C; 0.5 wt %) and vacuum drying the recrystallized polymer after filtration from the cooled (20 ° C) solution. The specimens consisting of combinations of the two polyethylenes as foils or test bars in contact with each other or solid state mixed powders were prepared in special moulds in a oven. The temperature regime was as follows: melting at