In this work the settling velocity of a single sphere in a viscous suspension of larger, neutrally buoyant spheres, was experimentally investigated for dilute and semi-dilute conditions. In dilute conditions, the results are in broad agreement with Batchelor's theoretical predictions. For more concentrated suspensions, where theoretical predictions are not available any longer, the results could be well represented by less rigorous approaches, such as the pseudo-fluid simplification. (C) 2011 Elsevier B.V. All rights reserved.