Flows of concentrated suspensions at low Reynolds number through an asymmetric T-junction bifurcation composed of rectangular channels are studied experimentally using nuclear magnetic resonance imaging. In contrast to the unequal division of a uniform concentration material, the suspension and the neutrally buoyant, noncolloidal particles are almost equally partitioned between downstream branches, and motion of particles across the dividing stream surface is deduced to occur at the bifurcation. We attribute the rearrangement of particles to enhanced spreading of high concentration (and therefore high local viscosity) regions of the suspension toward the side branch. The partitioning is accompanied by lateral asymmetry in the concentration and velocity profiles of the downstream branches, although the inlet profiles are symmetric. In the spanwise direction, inhomogeneous concentration distributions that develop upstream persist throughout the inlet and downstream channels. Overall, the fractions of the flow rate and cross-sectional area flowing into the side branch vary slightly with bulk particle volume fraction. Also, inertial effects likely cause an observed shift of the dividing streamline toward the side branch as the flow rate increases, while the flow rate and particle flux fractions entering the side branch hardly change. Finally, directional asymmetry is observed between diverging and converging flows. (C) 2008 The Society of Rheology.