We investigate the flowing behavior of dense Suspensions of noncolloidal particles, by coupling, macroscopic rheometric experiments and local velocity and concentration measurements through magnetic resonance imaging (MRI) techniques. We find that the flow is localized ill low velocities. an the local laws inferred from macroscopic rheometric d that the material is inhomogeneous: observations must then be reinterpreted in light of these local observations. We show that the short time response to a velocity step allows dense suspensions to be characterized locally: they have a purely Viscous behavior, without any observable influence of granular friction. In the "jammed" zone, there may be a contact network, whereas in the sheared zone there are only hydrodynamic interactions: localization consists of a change configuration at the-rain scale. From the concentration and velocity profiles, we provide for the first time local measurements of the concentration dependence of viscosity, and find Krieger-Dougherty law eta(phi) = eta(0)(1 - phi/0.605)(-2) to apply. Shear-induced migration is almost instantaneous ill contrast to most other observations, and implies that the diffusion Coefficients depend Strongly Oil the concentration. We finally propose a simple Constitutive law for dense Suspensions, based oil a purely viscous behavior. that accounts for all the macroscopic and local observations. (c) 2000 The Society of Rheology.