X-ray microtomography is a powerful non-invasive visualisation technique which can be advantageously used to get a better understanding or dynamic adsorption processes. In the present work, this technique is shown to be able to detect wall effects during the dynamic adsorption of methyl iodide on activated carbon filters. The analysis of transversal cross-sections along the filter height clearly shows the existence of radial concentration profiles. These radial adsorption profiles are directly linked to velocity profiles due to a higher permeability at the wall. Obtaining Such in situ information constitutes a real progress in order to validate simulation models allowing predicting reliable breakthrough times. (C) 2008 Elsevier B.V. All rights reserved.