We report the first application of magnetic resonance techniques to explore the spatial variation in chemical conversion of a catalysed reaction occurring within a fixed-bed reactor. The reaction studied is the liquid-phase esterification of methanol and acetic acid, catalysed by a proton exchange (Amberlyst 15 ion exchange resin) catalyst. This esterification is considered as a generic liquid-phase reaction, for which the extent of reaction is measured non-invasively, in situ, by monitoring the 1 H chemical shift of the hydroxyl resonance associated with fluid in the inter-particle space of the bed. The paper highlights the application of one-dimensional chemical shift imaging and volume selective magnetic resonance spectroscopy techniques to measure directly and quantitatively the spatial distribution of chemical conversion within a fixed-bed of catalyst particles. In the specific case study considered here it is shown that while conversion within the bed is homogeneous under batch reaction conditions, as expected, when reaction occurs under flowing conditions fractional variations in steady-state conversion of up to similar to20% exist within transverse sections through the bed, perpendicular to the direction of superficial flow. We suggest that magnetic resonance visualisation techniques are now able to provide a quantitative tool to aid in the integrated design of catalyst and reactor.