To study how the properties of extruded medium-density polyethylene products are influenced by the microstructure, rodlike samples, whose morphology can be changed under appropriate processing conditions, were produced by extrusion. A special extrusion line was developed consisting of an extruder equipped with a cylindrical die, thermal separator, lubrication unit, and cooling die. A wide range of representative morphologies was achieved using various temperatures of polymer melt and of the cooling die (calibration unit). A significant structural gradient, determined by differential scanning calorimetry (DSC), was found in all extruded rods, depending on the thermal conditions. The molecular orientation through the section of the rods, resulting from the shear during the extrusion, was determined by Fourier transform infrared (FTIR) spectroscopy and by thermal relaxation, showing good agreement between both methods.