A slight modification of the dissipation term in the Leonov model using relaxation time-dependent adjustable parameters is proposed to increase the model capability to represent elongational flow behavior. The fitting/predicting capabilities of the proposed modified Leonov model are compared with the eXtended Pom-Pom model and modified White-Metzner model in steady shear and uniaxial extensional flows of LDPE, mLLDPE and PVB melts in a wide range of deformation rates. The input low-shear-rate viscosity and first normal stress coefficient data was measured on the advanced rheometric expansion system (ARES) Rheometrics parallel-plate rheometer, whereas the RH7-2 capillary rheometer was used for the determination of shear viscosity (capillary), first normal stress coefficient (slit die) and uniaxial extensional viscosity (Cogswell method). A newly developed 'effective entry length correction' was applied to deal with all uniaxial extensional viscosity data. (C) 2003 Elsevier B.V. All rights reserved.