An electrodiffusion measurement system has been developed and used in a packed bed with single phase liquid flow. It is based on a tri-segmented microelectrode flush mounted at the surface of an Altuglass sphere equator area. Four of such probes are placed in lozenge form in the packed bed thus constituting a pore where the measurements were carried out. Each probe is equipped with a rotating system which allows the probe to turn around its vertical axis and consequently allows the microelectrode to cover all azimuthal positions. The tri-segmented microelecrodes are first calibrated in a separate experimental setup where the hydrodynamics is controlled and then placed in the packed bed. The results presented concern mainly the velocity gradient and local flow direction measurements. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.