Nonuniform velocity and concentration distributions have been measured for suspensions of small, negatively buoyant particles flowing in horizontal tubes. All measurements were performed during statistically steady flow conditions with average fluid velocities up to 25 cm/s. The mean particle concentration φ̄sranged between 0.0≤φ̄s≤0.39. Time‐averaged measurements were recorded noninvasively by using a three‐dimensional, flow‐compensating, nuclear magnetic resonance technique. This method spatially resolves both the fluid velocity and particle concentration distributions from a single imaging experiment and permits detailed analysis of the flow‐induced structure of nondilute suspensions.