Based on results of previous work high-density polyethylene has been modified with high energy electrons either before or after injection moulding in order to compare the influence of sequences of processing (irradiation – forming). Electron treatment of polyethylene was performed under inert atmosphere at different states of aggregation. The polymer was irradiated in the solid state as well as in the molten state under stationary and dynamic conditions. The process induced morphological and mechanical properties have been investigated using light microscopy, transmission electron microscopy as well as thermal analysis and tensile tests. Changes of molecular mass were measured with gel permeation chromatography. The results have shown that it has to distinguish between process-related properties affected by different thermal preconditions like cooling rate or influenced by electron treatment for instant absorbed dose from properties dependent on the process order.