Stress oscillations were produced and analyzed in partly-crystalline syndiotactic polypropylene (sPP) and in poly(ethyleneterephthalate) (PET) in cold drawing experiments. Strain oscillations, which always occur in connection with stress oscillations, were also investigated. The experiments were performed varying the parameters temperature, sample geometry and drawing velocity. This article gives first results of our investigations, which show discrepancies to the existing theories.