Dense particle suspensions are widely encountered in many applications and in environmental flows. While the large part of studies investigates their rheological properties in laminar flows, little is known on the behavior of these suspensions in the inertial and turbulent regimes. The present talk aims to fill this gap by discussing the transitional and turbulent behavior of a Newtonian fluid laden with neutrally-buoyant rigid spheres at relatively high volume fractions in a plane channel.