This study looks at the flow of a gelled suspension of spheres in a sudden three-dimensional (3D) expansion. The spheres are large non-colloidal objects and the ratio of pipe diameter to sphere diameter in the upstream pipe is 4 to 1. Model suspensions highly stabilised with respect to sedimentation or creaming were prepared. In static conditions, the spheres cannot move under gravity force effects. Nuclear magnetic resonance imaging (NMRI) was used to obtain images of the spatial distribution of the spheres in the bulk of the suspension. It was thus possible to reveal the structures formed by flow in the expansion as a function of plasticity, inertia and 3D effects. Various regimes were identified, including one associated with instabilities in the upstream pipe. (c) 2005 Elsevier B.V. All rights reserved.