A contradiction has recently appeared between the current understanding of entangled polymers in nonlinear shear flow and new experimental observations based on highly entangled monodisperse 1,4-polybutadiene solutions. Using entangled polydisperse solutions, we have examined the universality of the new revelation that any sufficiently entangled and relatively monodisperse polymeric fluids undergo a flow transition in simple shear when the applied stress is comparable to the plateau modulus. Indeed, a similar flow transition, marking the onset of bulk chain disentanglement, as previously observed for polybutadiene solutions in controlled-stress experiments, can also be observed in less entangled and more polydisperse polyisoprene solutions, whereas controlled-rate experiments do not reveal any transitional behavior. (C) 2004 Wiley Periodicals, Inc.