Specifies methods for testing plastic melts subjected to shear stresses at rates and temperatures approximately to those arising in plastic processing. Testing plastic melts in accordance with these methods is necessary since their fluidity is generally not dependent solely on temperature, but also on other parameters, e.g. shear rate and shear stress. Methods for assessing extrudate swelling have also been included. The rheological techniques described are not limited to wall-adhering thermoplastic melts, the methods used for determining the shear rate and shear viscosity, however, are invalid for not wall-adhering materials.