The distribution of the fluid phases in trickle beds is usually investigated using visualization techniques like computed tomography or colorimetrics or with annular collecting devices. These experimental techniques suffer from an inability to provide data at a spatial and temporal resolution suitable for investigating the stability of the liquid flow pattern at the particle scale. Presently, rapidly acquired X-ray radiographs are used to shed new light on various aspects of trickle flow. Radiography derived liquid saturation values of a section of the bed correspond closely to gravimetrically determined saturations. It is demonstrated that the flow patterns encountered in multiple hydrodynamic states can be successfully visualized using X-ray radiography. Trickle flow is stable in all but one of the pre-wetting modes investigated. In the Levec mode, low frequency particle scale instability exists at sparsely dispersed locations in the bed. Although both the type of flow pattern and the liquid saturation are reproducible, the actual flow patterns themselves are shown not to be. In general, the stability of the flow pattern validates the use of tomographic and colorimetric methods for investigating trickle flow hydrodynamics. (c) 2007 Elsevier B.V. All rights reserved.