Lodge's rubberlike-liquid theory is a valid description of material behaviour at small strains. Unfortunately, it fails in the nonlinear region, i.e. at higher strains. In shear flows, the phenomenon of shear thinning, which is a fundamental property of nearly all polymer fluids, is not explained. From a point of view of Lodge's equation the deviation of material behaviour from theoretical prediction in uniaxial elongational flow is one of strainthinning, too, and not of strain thickening. By comparison of experimental stress growth and stress relaxation data with theoretical predictions of the rubberlike liquid constitutive equation the conclusion can be drawn that the structure of the temporary network of a polymer melt is destroyed increasingly at higher strains. The number of entanglements decreases with increasing strain. For simple shear and uniaxial extension of a well-defined polyethylene melt the strain dependence of the number of entanglements is given and compared.