In the present work an effort is made to determine the suspension speed of microcarriers in an orbitally shaken bioreactor of cylindrical geometry, and to assess the associated two-phase flow by means of Particle Image Velocimetry (Ply). Microcarrier technologies are commonly used in the bioprocess industry to culture adherent-dependent cells in three dimensional flow. Commercial GE Cytodex microcarriers were employed throughout this study to best mimic the flow conditions occurring in a bioreactor under standard operating conditions. Suspension speed measurements were obtained at different solid concentrations, that are typical for cell cultures, and for different combinations of orbital to cylinder diameters' ratio, d(o)/d(i) (c = 2.5-12.5 g/L; d(o)/d(i) = 0.2-0.7; N = 0-200 RPM). The current two-phase Ply results show that mean flow dynamics occurring in the cylindrical bioreactor are not significantly affected by the presence of the microcarriers, and that their suspension is directly associated to the flow transition reported by Weheliye et al. (2013). The flow scaling law included in their study can be successfully employed to predict the full suspension speed across bioreactors of different scales and working under different operating conditions (i.e. inner diameter of the cylinder, d(i), orbital diameter, do, and filling volume, V-f). (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.