Recent data by Hassager and co-workers [Bach et al. Macromolecules 2003, 36, 5174] of elongational viscosity of nearly monodisperse polystyrene melts are interpreted by including in the classical tube theories for entangled polymer dynamics an interchain repulsive contribution. The proposed theory predicts the observed power law of eta(el) vs epsilon in a straightforward way and qualitatively explains the observed scaling with the polymer molecular mass. Possible generalizations are discussed.