The behaviour of the viscous pressure as a function of the shear rate is studied for a non-Newtonian polymer solution in a cone-and-plate device, in the presence of a shear-induced concentration banding transition. In this transition, where the system splits into two bands with different polymer concentrations, the slope of the viscous pressure is shown to have a clear discontinuity. This behaviour is rather different from the one observed in shear banding in liquid crystals, where concentration remains homogeneous but the system splits into two bands with different orientations and shear rates. (C) 2003 Elsevier Ltd. All rights reserved.