Wall slip during flow of viscoelastic fluids through cylindrical tubes and the surface character of the extrudate have been studied using aqueous solutions of polyvinyl alcohol and sodium borate. Experiments with rough and smooth tubes of Plexiglas and aluminum show that the nature of the flow is highly dependent on the characteristics of the tube surface. For example, at apparent wall shear rateγ̇a=7.6 sec−1in rough and smooth Plexiglas tubes with inside diameter of 0.638 cm, a solution containing 3.5% polyvinyl alcohol and 3.5%Na2B4O7⋅10H2Oregistered a pressure drop through the rough tube more than twice that measured for the smooth tube. Also, distortion was severe for the extrudate from the rough tube atγ̇a=11.3 sec−1,but comparable distortion from the smooth tube did not appear untilγ̇a>30 sec−1.A hot‐film anemometer has been adapted to study slip near the wall of a conduit. With hot‐film and reservoir pressure measurements we have shown that the microscopic nature of a tube wall can promote or inhibit slip, and that slip reduces extrudate swell and delays the onset of severe extrudate distortion. We have observed a transient effect termed slip‐initiated stress overshoot, and, with a Teflon tube, a region in which self‐oscillation occurs.