For two linear polyethylene melts, a HDPE and a LLDPE, Rheotens experiments at constant extrusion pressure and different extusion temperatures are reported. While at sufficiently small extrusion pressure Rheotens mastercurves were found, various deviations from the mastercurves were observed at higher extrusion pressures. By use of capillary rheometry and Mooney＇s method, these deviations could be attributed to a stick-slip transition in the extrusion die, and, in the case of LLDPE, to partial wall slip below the stick-slip transition.