We demonstrate the application of magnetic resonance imaging (MRI) to provide quantitative visualisation of two-phase flow in two different reactor environments. First, visualisation and analysis of bubble-train flow within individual channels in a ceramic monolith are presented. Images are acquired over time-scales of 146ms, thereby enabling the movement of individual gas bubbles to be followed in real time. From these data, distributions of bubble size and velocity are obtained. Second. MRI is used to obtain measurements of liquid hold-up and wetting efficiency during co-current air-water trickle flow in fixed beds of packings of cylindrical, porous alumina extrudate. Data are reported for a constant gas superficial velocity of 3 1.3 mm/s. and liquid superficial velocities in the range 0.1-6 mm/s. The dynamic liquid hold-up data are well modelled using the percolation analysis of Crine et al. [Chem. Eng. Sci. 47 (1992) 2263]. (C) 2003 Elsevier Science B.V. All rights reserved.