The shear dependent viscosity and related properties of a number of ethylene polymers of differing molecular structure have been characterized using a capillary extrusion rheometer. The structural aspects of interest were average molecular weight, branching, and the presence of strong intermolecular secondary forces. It was found that average molecular weight influences the degree of shear dependence of the viscosity, branching affects both flow activation energy and the nature of the observed “melt fracture” phenomenon, and intermolecular hydrogen bonding enhances viscosity and activation energy and leads to increased shear dependence of flow behavior. The results are interpreted in terms of specific molecular mechanisms.