We present experimental data demonstrating wall slip of high temperature polymer melts at high shear rates (up to approximate to 70 s(-1)) without pressure and viscous heating effects. Results for polydisperse (linear low density polyethylene) and monodisperse (polystyrene) melts are presented. For the monodisperse case two distinct regimes of slip are seen: (1) a low shear rate regime in which the slip velocity increases slowly with shear rate (weak slip) and (2) a high shear rate regime in which the increase is dramatic (strong slip). Through scaling of our shear stress/shear rate data we demonstrate that the crossover between the two regimes occurs when the bulk polymer chains are effectively disentangled. These findings are in qualitative agreement with molecular models of slip which invoke an entanglement-disentanglement scenario for the transition from weak to strong slip. The polydisperse system shows less critical sip behaviour and the slip velocity increases; yet, the increase is less dramatic than the monodisperse system. (C) 2000 Elsevier Science B.V. All rights reserved.